Introduction

With at least 2000 species, the Justicieae (Acanthaceae: Acanthoideae) are the largest tribe of Acanthaceae, and are the source of numerous taxonomic challenges due to complex morphological variation including frequent homoplasy (Daniel et al. 2008; Kiel et al. 2017, 2018; McDade et al. 2018, 2021; Darbyshire et al. 2019a; Manzitto-Tripp et al. 2021). Particularly problematic is generic delimitation of Justicia L. and allies in the subtribe Justiciinae (sensu Manzitto-Tripp et al. 2021), where molecular phylogenetic data demonstrate that several morphologically discrete genera are nested within Justicia s.l. (Kiel et al. 2017, 2018). To maintain a broadly circumscribed Justicia as defined in most modern taxonomic treatments, the entire Justiciinae would have to be treated under Justicia s.l., but this is highly undesirable as it would result in the loss of much valuable taxonomic information. The most favourable alternative option is to disaggregate Justicia and to recognise discrete, well-supported and well-sampled clades as separate genera, backed by knowledge of taxonomically informative morphological traits (Darbyshire et al. 2019a, 2020).

One such genus nested within the Justiciinae is Monechma Hochst. (or Justicia sect. Monechma (Hochst.) T.Anderson), a striking radiation of African plants. Species of Monechma range throughout sub-Saharan Africa, but are most diverse and abundant in the savannas, deserts, and shrublands of southwestern Africa, especially portions of Namibia and southern Angola (Munday 1983; Darbyshire et al. 2020). In this region, plants of Monechma comprise some of the most dominant elements of landscapes, together with species in three other parallel radiations of Acanthaceae, Petalidium Nees, Barleria L., and Blepharis Juss. (Vollesen 2000; Tripp et al. 2017; Darbyshire et al. 2019b, 2020, 2021). This ecological significance has motivated recent interest in Monechma, where a RADseq phylogenetic analysis which included over 75% of the currently accepted species, resolved relationships amongst this important group (Darbyshire et al. 2020).

Phylogenetic results presented in Darbyshire et al. (2020) confirmed earlier results based on evidence from six molecular markers (Kiel et al. 2017) that Monechma s.l. in fact comprises two widely separated lineages, named Monechma Groups I and II. The RADseq study, however, refined delimitation of these two clades from the earlier study by Kiel et al. (2017). Specifically, it revealed that the group of perennial (rarely annual) herbaceous taxa from the savanna biome of tropical Africa, with usually terminal spiciform inflorescences and bracts ± highly modified from the leaves (M. ciliatum (Jacq.) Milne-Redh., M. scabridum S.Moore and allies) is allied to the group of mainly perennial shrublets with ± undifferentiated bracts (M. cleomoides (S.Moore) C.B.Clarke and relatives) primarily from the succulent biome of southern Africa (Darbyshire et al. 2020). This tropical savanna group was not sampled in the earlier study of Kiel et al. (2017) but based on morphological extrapolation, both that study and Darbyshire & Goyder (2019) later surmised that the tropical savanna group was allied to species of the M. debile (Forssk.) Nees complex, which are mostly annual, ruderal species with spiciform inflorescences and highly modified bracts. However, the RADseq analysis demonstrated that M. debile and allies form their own discrete clade, closely allied to Justicia sect. Harnieria (Solms) Benth. Study of a range of morphological traits revealed that the two clades of Monechma under their revised circumscriptions could be separated by differences in inflorescence and seed characters (Darbyshire et al. 2020). It was therefore concluded that these two clades should be elevated to distinct genera, but Darbyshire et al. (2020) refrained from nomenclatural changes.

In the present work, we recognise Monechma Groups I and II at the generic rank as Meiosperma and Pogonospermum respectively, and provide the appropriate new combinations following a nomenclatural review. We also build on the morphological studies of Darbyshire et al. (2020) to propose a formal sectional classification for Monechma Group II (Pogonospermum).

This is an early step in the process of redefining the genera within Justiciinae. Moving forward, further detailed studies employing NGS techniques comparable to that presented in Darbyshire et al. (2020), are required across Justiciinae in order to provide a revised classification. To this end, a RADseq analysis of the New World Justiciinae is currently in progress (C. A. Kiel et al. in prep.).

Materials and Methods

The present contribution consists of two parts. The nomenclatural study is based on a review of relevant literature on Monechma and allied genera, including protologues and relevant Flora accounts. The taxonomic study is based on examination of herbarium collections and images of species in situ, in combination with the phylogenetic results of the RADseq dataset of Darbyshire et al. (2020). Most observations were made on herbarium specimens held at COLO, K, RSA and WIND (herbarium abbreviations follow Thiers, continuously updated), with additional observations made via access to digital images of type specimens on JSTOR Global Plants (https://plants.jstor.org/) and other online repositories of herbarium specimen images.

For species not sampled in Darbyshire et al. (2020), best estimations for taxonomic placement were made based on morphological traits. Type specimens are cited for the accepted names; those seen by one or more of the authors are marked with an “!”; those seen as digital images are marked with an “*”.

Species delimitation follows a combination of Hedrén (2006a, 2006b), Munday (1995), Vollesen (2010, 2015) and Darbyshire & Goyder (2019), with some modifications based on the current study. For each accepted species, the geographic range is derived from herbarium collections, online databases (notably Plants of the World Online, POWO 2020) and relevant taxonomic literature, principally those cited above.

In the section on nomenclatural renovations, a “^” denotes that the species was sampled in the RADseq study (Darbyshire et al. 2020).

Results and Discussion

Applying the correct generic names to Monechma Group I and Monechma Group II

Monechma was first described by Hochstetter (1841: 374) who included two species, both based on collections from the expedition to Nubia by Theodor Kotschy: M. bracteatum Hochst. (Kotschy it. nubico 261) and M. hispidum Hochst. (Kotschy it. nubico 239). Later, having seen further cultivated material of Monechma from seeds grown on from Kotschy’s collections, Hochstetter (1844: 5) chose to separate Monechma into two genera and described Pogonospermum Hochst. based on his M. hispidum (= P. hispidum (Hochst.) Hochst.) plus a second species, P. ciliare that was based on Justicia ciliaris, which Hochstetter wrongly attributed to Vahl, having overlooked Linnaeus’ (1781) earlier application of this name. Hochstetter also erred in using the epithet “ciliare” given that he also included the earlier name J. ciliata Jacq. in synonymy. Hochstetter cited differences in seed characteristics as justifying the recognition of two genera, i.e., Monechma sensu stricto has glabrous seeds, whilst the seeds of Pogonospermum have tufts of trichomes at the base and apex. By splitting Pogonospermum from Monechma, Hochstetter indicated that Monechma was now to be based on M. bracteatum and, indeed, Monechma was subsequently lectotypified with M. bracteatum by Phillips (1951).

In describing Monechma and Pogonospermum, however, Hochstetter had overlooked two earlier generic names of relevance to this group that require consideration here. Firstly, Rafinesque (1838: 64) described Meiosperma based on Dianthera debilis Forssk. Rafinesque noted that his new genus differed from Dianthera L. (= Justicia in current classifications; with Justicia sect. Dianthera (L.) V.A.W.Graham being exclusively New World as currently circumscribed; Graham 1988) in having single-seeded capsules, which was clearly a mistake as D. debilis is 2-seeded. He went on to note “…thus not even of this family, are the cells monosperm? The cor[olla] is bilabiate but undescribed. Type D. debilis Forsk. Vitm.” (p. 64). This suggests that Rafinesque did not see the material in the Forsskal herbarium on which D. debilis was based, rather he was reliant on Vitman’s (“Vitm.”) description of this species in his Summa Plantarum (Vitman 1789: 46), who recorded this species as being monospermous. Vitman’s record was, in turn, based upon Forsskål’s (1775) description of D. debilis in which he stated in error “capsula bilocularis, monosperma” (p. 9). It is perhaps on the basis of this perpetuated error in recording the number of seeds per capsule that Hochstetter overlooked Meiosperma when describing Monechma. However, an alternative explanation may relate to Rafinesque’s work being widely rejected in the biological community at that time (Boewe 2005) and so it may have been dismissed by Hochstetter. Wood et al. (1983) note that there are two specimens in the Forsskal herbarium with the name Dianthera debilis: microfiche 38: II. 3–4 and 38.II.5–6, and that they represent different species. Forsskal 38: II.3–4 is an informative specimen, with an open corolla and mature fruits and seed. This is clearly the specimen from which the name D. debilis has been applied in subsequent works (e.g. Nees 1847; Clarke 1900) and was selected as lectotype by Wood et al. (1983). Forsskal 38.II.5–6, although superficially similar in inflorescence form, is actually referable to Ecbolium violaceum (Vahl) Hillcoat & J.R.I.Wood. Irrespective of these complications, Meiosperma was validly published with D. debilis as the type species. Rafinesque (1838) did not make the new combination for this species in Meiosperma, but this is acceptable under the Botanical Code (Turland et al. 2018).

As first noted by Hochstetter (1843), Dianthera debilis and Monechma bracteatum are closely allied species and have often been united in past taxonomic treatments, under M. debile (Forssk.) Nees s.l. (e.g. Munday 1995; Welman 2003; Ensermu 2006; Klaassen & Kwembeya 2013). Both our RADseq dataset (Darbyshire et al. 2020) and earlier phylogenetic studies (Kiel et al. 2017) confirm a close relationship between these two species within Monechma Group I. Therefore, Meiosperma Raf. is the oldest valid name for Monechma Group I sensu Darbyshire et al. (2020) and has priority over Monechma Hochst.

Secondly, Endlicher (in Endlicher & Fenzl 1839: 81) described Schwabea, with a single species, S. modesta Endl., based on a Kotschy collection from tropical East Africa (probably Sudan) that was grown in cultivation in Charles von Hügel’s botanic garden in Hietzing, Vienna. Unfortunately, the Kotschy specimen in question was not numbered, nor was the precise collecting locality cited in the protologue, hence a corresponding herbarium collection is difficult to trace with certainty. Endlicher described this plant as having four didynamous stamens, which would not fit the genera allied to Justicia. However, in de Candolle’s Prodromus, Nees (1847) stated that he considered Endlicher to have been mistaken in his recording of the number of stamens and he equated Schwabea with Hochstetter’s Pogonospermum, reducing the latter to synonymy. Nees proposed the new combination Schwabea ciliaris (Vahl) Nees, with S. modesta, P. ciliare and P. hispidum all listed in synonymy. He also described a second species, S. spicigera Nees, with two varieties, both based on Heudelot specimens from “Senegambia”. In Flora of Tropical Africa, Clarke (1900) disagreed with Nees’ interpretation of Schwabea and excluded it from his “Eu-Justicieae” based on it having four stamens. Clarke reverted to Hochstetter’s original (1841) circumscription of Monechma, reuniting it with Pogonospermum and with Schwabea sensu Nees (which, confusingly, he used as the name for a proposed section of Monechma). Clarke’s view has since prevailed for over a century, except that some authors (e.g. Hedrén 1990, 2006b; Vollesen 2010, 2015; Manning & Goldblatt 2014; Darbyshire & Goyder 2019) have treated Monechma as a section of Justicia. Hence Pogonospermum ciliare and P. hispidum are currently treated as synonyms of either Monechma ciliatum (Jacq.) Milne-Redh. or Justicia ciliata Jacq.

Endlicher’s (in Endlicher & Fenzl 1839) Latin description of Schwabea modesta is thorough and, although some details of the plant do seem to align with Monechma ciliatum, there are some anomalies, not least of which is the recording of four didynamous stamens. Whilst some species of Acanthaceae that usually have two fertile stamens can occasionally have aberrant flowers with four stamens perfected (McDade et al. 2021), particularly when in cultivation, this is rare in taxa that lack staminodes, as is the case in the Justicioid Lineage. Further, Endlicher recorded the seeds of S. modesta as having hygroscopic trichomes, which would not fit with M. ciliatum, unless he misinterpreted the bristly trichomes of that species. Endlicher (in Endlicher & Fenzl 1839) suggested a possible affinity with his own genus Russeggera Endl. (= Lepidagathis Willd.) and this could potentially fit with the description, although no known species of Lepidagathis from East Africa fit with the description of S. modesta. Meisner (1840) subsequently reaffirmed this close relationship by placing Russeggera and Schwabea in a separate tribe of Acanthaceae, Russeggereae. The available evidence therefore suggests that Clarke (1900) was correct in his assertion that Nees (1847) erroneously equated Schwabea with Pogonospermum, and we consider Schwabea to be an unplaced name Indeed, it was treated as such in the recent reclassification of Acanthaceae (Manzitto-Tripp et al. 2021).

Monechma ciliatum is somewhat unusual in its seed indumentum in comparison to other known species of Monechma Group II, but it is nevertheless confirmed as a member of that clade in the study of Darbyshire et al. (2020), which rejected the exclusion of M. ciliatum from Monechma Group II (P < 0.001; see Table 2 of Darbyshire et al. 2020). In following Clarke (1900) and rejecting Schwabea s.s., Pogonospermum is therefore the earliest name for Monechma Group II sensu Darbyshire et al. (2020). The word root of the name Pogonospermum (“bearded seeds”) is not ideal in view of the fact that, although several species in this clade have pubescent seeds, only those of M. ciliatum could be described as “bearded”. We are nevertheless obliged to adopt this generic name for this clade if it is to be recognised as a discrete genus, as proposed below.

Should the generic name Monechma be conserved?

An alternative to resurrecting both Meiosperma and Pogonospermum for Monechma Groups I and II would be to propose to conserve Monechma over one or other of these names. The obvious choice here would be to propose to conserve Monechma over Meiosperma given that the types of these two names are congeneric. As Meiosperma has not been used since Rafinesque’s (1838) original publication of the name, it is plausible that a proposal to conserve Monechma over Meiosperma might be successful. However, there are problems with this choice. Firstly, as the large majority of diversity within Monechma s.l. falls within Group II (Pogonospermum), this would not result in much greater nomenclatural stability, as the names for only three currently accepted species (Monechma bracteatum, M. debile and M. monechmoides (S.Moore) Hutch., representing only half of the currently accepted species in Group I and only 7.5% of the species diversity across Monechma s.l.) would be retained. Secondly, the name Monechma debile is problematic as the circumscription of this species has varied widely in the past and, in its broadest sense, has been applied to most members of Monechma Group I, including to the more widespread and abundant taxon and type of Monechma, M. bracteatum (e.g. see Munday 1995; Ensermu 2006). Given this confusion, it is not greatly desirable to maintain the name Monechma debile.

The second alternative would be to propose to conserve Monechma over Pogonospermum. This would have the advantage of maximising nomenclatural stability given that 26 of the 34 currently accepted species in Group II have a name available in Monechma. However, this would require a proposal to change the lectotype of Monechma, from M. bracteatum to M. hispidum. The resultant significant change in circumscription of Monechma — including the preclusion of the most widespread, common and familiar taxa, i.e., M. debile and its allies — would likely create significant confusion for non-specialists over application of the name Monechma. Given that many species in Group II are highly range-restricted and little-known species and only rarely cited in the literature (e.g., a search in May 2021 for Monechma in Google Scholar returns only 1,160 results), it would seem inappropriate in this case to propose the rather drastic change in the lectotype, given the controversy over such a proposal. Furthermore, such a change would run contrary to the valid decision made by Hochstetter (1844) in terms of the segregation of Pogonospermum from his Monechma as discussed above.

In conclusion, it is our opinion that neither option for conserving Monechma is desirable and thus we propose to accept Meiosperma and Pogonospermum, and adopt the necessary nomenclatural changes.

Generic delimitation and infrageneric classification in Meiosperma and Pogonospermum

A summary phylogeny placing the newly resurrected genera Meiosperma (Monechma Group I sensu Darbyshire et al. 2020) and Pogonospermum (Monechma Group II sensu Darbyshire et al. 2020) in the context of related clades in Justiciinae is presented in Fig. 1, based on the results of the RADseq phylogeny in Darbyshire et al. (2020). In the Nomenclatural Renovations section below, we provide the new combinations in Meiosperma and Pogonospermum for all currently recognised members of Monechma or Justicia section Monechma. Table 1 provides a summary of these two genera and how they relate to the nomenclature in Darbyshire et al. (2020). The two genera can be separated by application of the key below.

Fig. 1
figure 1

Summary RADseq phylogeny of former members of Monechma s.l. and allied clades in Justiciinae; data summarised from Darbyshire et al. (2020).

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Table 1. Summary of taxonomy of former members of Monechma (or Justicia sect. Monechma) and relationship to clades recognised in Darbyshire et al. (2020).
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Key to distinguish the reinstated genera Meiosperma and Pogonospermum

  • Inflorescences of axillary or both axillary and terminal spikes; bracts elliptic, ovate or obovate, often imbricate, inflorescence units at each axil often > 1-flowered; seeds 2 – 3 mm diam., lenticular with a sharp rim, ± symmetrical in cross section and lacking a prominent ridge on one side, glabrous*................................................ ............................................................................................................................................................................Meiosperma

  • Inflorescences either axillary and single-flowered (bracts undifferentiated from the leaves) or in well-defined, mostly terminal spikes (bracts highly modified), rarely in axillary pedunculate fascicles; bracts in species with well-defined spikes usually narrow, linear to lanceolate, or rarely (in one species) broadly elliptic to obovate; seeds variable, often larger than 3 mm in diam. with a rounded rim (including in the single species with broad bracts) and/or variously pubescent, or if small and with sharp rim then asymmetric in cross section and with a prominent ridge on one side*.......................................................................................Pogonospermum *for illustration of the differing seed morphology, see Fig. 8 in Darbyshire et al. (2020).

Meiosperma

Meiosperma, as currently defined, comprises six accepted species and two undescribed taxa (Fig. 2, Table 1). These species are closely allied morphologically (although M. tetrasperma is notable for having 4-seeded capsules, the other species having only 2-seeded capsules), and no infrageneric taxa are proposed. Species delimitation in this group is challenging, with significant infraspecific variation noted in several of the widespread species as currently delimited. A full revision of Meiosperma is desirable, ideally supported by an expanded phylogenetic study.

Fig. 2
figure 2

Representative species of Meiosperma. A M. bracteatum (Mozambique); B M. monechmoides (Namibia). photos: a b. wursten; b e. a. manzitto-tripp.

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Both Kiel et al. (2017) and Darbyshire et al. (2020) noted a close relationship between Meiosperma (Monechma Group I) and a paraphyletic Justicia sect. Harnieria (Fig. 1). However, Darbyshire et al. (2020) noted that monophyly of sect. Harnieria cannot be rejected by the results from the RADseq analysis. Meiosperma and species in sect. Harnieria are easily separated by differences in seed sculpturing: seeds of the former are smooth whilst those of the latter are variously tuberculate (see Fig. 14 in Hedrén 1989 but note that 14H with smooth seeds is mislabelled as Justicia mollugo C.B.Clarke in sect. Harnieria when it actually represents South American J. peruviana Cav.; see also Fig. 12G – H in Kiel et al. 2017). It is also worth noting that some species of sect. Harnieria, such as J. diclipteroides Lindau and J. heterocarpa T.Anderson, are heterocarpic, and have winged indehiscent 1-seeded fruits in addition to the typical explosively dehiscent 4-seeded capsules (Hedrén 1989). In such cases the seeds in the indehiscent fruits are smoother than in the dehiscent fruits but still have some tubercles (see Hedrén 1989, Fig. 14D). This phenomenon of heterocarpy is not observed in Meiosperma.

In addition to the difference in seed sculpturing, the axillary inflorescences of Meiosperma are often more developed, forming spikes with broad imbricate bracts whilst those of sect. Harnieria are usually fasciculate. However, there is some overlap in inflorescence form, and Hedrén (1990) noted similarities in the structure of the cymose units within the inflorescences of members of these two groups. Darbyshire et al. (2020) provide further discussion on morphological similarities and differences between the two. Additional RADseq sampling in sect. Harnieria would elucidate the relationship between these taxa. Depending on the outcome of further studies, either sect. Harnieria will need to be elevated to generic status (Harnieria Solms) or Meiosperma will need to be expanded to include sect. Harnieria and so include taxa with both smooth and sculptured seeds. This would increase the size of Meiosperma significantly, as sect. Harnieria has c. 50 recognised species in Africa alone (Hedrén 1989, and with subsequent additions and modifications in e.g Vollesen 2010, 2015; Champluvier 2013).

Pogonospermum

Pogonospermum is a larger and morphologically more diverse genus than Meiosperma (as currently delimited — see above), with 34 species currently recognised and with at least two undescribed taxa. Darbyshire et al. (2020) discussed the infrageneric variation in this group and noted two major clades, the first (the “ciliatum/scabridum” clade) with pubescent seeds and the second with glabrous seeds. This second clade was further subdivided into four clades that can be separated based on variation in inflorescence form, venation of the calyx lobes and bracteoles, and seed shape. In the Taxonomic Renovations section, we formally recognise these clades as sections of Pogonospermum (Table 1), which can be separated using the key below. The “ciliatum/scabridum” clade of Darbyshire et al. (2020) is subdivided here, with Pogonospermum ciliatum (the type species of the genus) treated in its own section, separate from sect. Savannicola which contains the other species with pubescent seeds; these two sections are easily separated by differences in plant life form and seed indumentum. Therefore, six sections are recognised in Pogonospermum (Figs 1 & 3, Table 1).

Fig. 3
figure 3

Representative species in the sections of Pogonospermum. A sect. Pogonospermum: P. ciliatum (Mali); B sect. Savannicola: P. depauperatum (Guinea); C sect. Virgultorum: P. virgultorum (Angola); D sect. Tricostatum: P. rigidum (Angola); E sect. Serotinum: P. serotinum (Namibia); F & G sect. Aridicola: F P. cleomoides (Namibia), G P. grandiflorum (Namibia). photos: a q. luke; b c. jongkind; c, d d. goyder; e h. kolberg; f i. darbyshire; g e. a. manzitto-tripp.

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Key to the six sections of Pogonospermum

  • 1. Annual herbs; seeds with tufts of bristly trichomes at apex and base....................................sect. Pogonospermum

  • Usually perennial herbs or shrublets; if annual herbs then seeds glabrous...............................................................2

  • 2. Bracts largely undifferentiated from leaves or only gradually and slightly modified towards apex of fertile branches; flowers therefore appearing axillary or at most forming a weakly-defined and leafy spike.............................................................................................................................................................sect. Aridicola

  • Bracts clearly modified from leaves; inflorescences of well-defined terminal or terminal and axillary spikes, or rarely of axillary pedunculate fascicles..........................................................................................................................3

  • 3. Seeds white-puberulous at least when young.............................................................................................sect. Savannicola

  • Seeds glabrous...................................................................................................................................................................4

  • 4. Calyx lobes and bracteoles each with 3 prominent veins externally, these often darker in colour than the intercostal areas ............................................................................................................................................................sect. Tricostatum

  • Calyx lobes and bracteoles with veins either all inconspicuous or with only the midvein prominent and not darker than the intercostal areas...................................................................................................................................5

  • 5. Plants of fire-prone habitats; marked by herbaceous growth from a woody base and rootstock................................................................................................................................................sect. Virgultorum

  • Plants not of fire-prone habitats; subshrubs with woody mature stems...........................................sect. Serotinum

The largest section in Pogonospermum is sect. Aridicola that comprises 17 species, many of which are confined to the deserts and xeric bushlands of the succulent biome in southwest Africa (Munday 1983; Darbyshire et al. 2020). In Darbyshire et al. (2020), P. incanum (Nees) I.Darbysh. & Kiel was resolved as sister to the remainder of the southern African members of this section. Pogonospermum incanum, recorded from Botswana, Namibia and South Africa, is notable for having biramous trichomes on the vegetative parts. Although only P. incanum has been sampled in the current study, we tentatively hypothesise that, based on morphology, P. crassiusculum (P.G.Mey.) I.Darbysh. & Kiel, P. robustum (Bond) I.Darbysh. & Kiel and P. saxatile (Munday) I.Darbysh. & Kiel may be allied to P. incanum, as earlier indicated by Munday (1995). These species all share rather fleshy and narrow, obovate to linear-oblanceolate or linear-terete leaves, and an indumentum comprising complex trichomes that are either biramous, as in P. incanum and sparsely so in P. saxatile, or are anvil-shaped, i.e. hairs with a short stalk terminated by a single arm, as in M. crassiusculum and P. robustum (Munday 1995). It would be desirable to include these species in a future expanded RADseq dataset to confirm or refute their alliance to P. incanum. The other species of sect. Aridicola lack these complex trichomes on the leaves, although P. calcaratum (Schinz) I.Darbysh. & Kiel has branched trichomes on the stems (Munday 1995).

Pogonospermum incanum and its putative allies share a striking resemblance to the southern African Justicia cuneata Vahl (see Immelman 1995). Justicia cuneata comprises three subspecies, two of which have glabrous leaves, but the third, subsp. hoerleiniana (P.G.Mey.) Immelmann from southwest Namibia, has dense swollen anvil-shaped trichomes throughout its vegetative portions. Justicia cuneata has rarely been collected in fruit and we have not seen mature capsules or seeds of this species; Immelmann (1995) describes the capsules as 1-seeded, clavate and hard in texture — an unusual arrangement for Justicia and indeed for members of Justiciinae in general although, as noted above, indehiscent single-seeded fruits are known in some heterocarpic species of Justicia sect. Harnieria (Hedrén 1989). Justicia cuneata has not, to our knowledge, been included in any molecular phylogenetic studies to date and it should be considered a priority for future studies to determine whether it is allied to the P. incanum group or if (as is quite possible) this represents a case of convergent evolution.

Nomenclatural Renovations in Meiosperma and Pogonospermum

Below we provide a species inventory for the two resurrected genera Meiosperma and Pogonospermum, formalise the necessary new combinations and select lectotypes where required and appropriate. We also formally describe the newly recognised sections within Pogonospermum.

It is acknowledged that species delimitation requires further research in some groups of both Meiosperma and Pogonospermum. Furthermore, some species currently placed within Justicia may ultimately prove to be members of one or other of these two genera. For example, it is quite possible that the recently described Justicia nanofrutex Champl. (Champluvier 2013) is a member of Pogonospermum, however the fruits of this species have not been seen to date.

Meiosperma Raf. (Rafinesque 1838: 64). Type species: Meiosperma debile (Forssk.) I.Darbysh. & E.Tripp (basionym: Dianthera debilis Forssk.).

Monechma Hochst. (Hochstetter 1841: 374). Type species: Monechma bracteatum Hochst., lectotype, selected by Phillips (1951: 715) (= Meiosperma bracteatum (Hochst.) I.Darbysh. & E.Tripp), synon. nov.

1. ^Footnote 11Meiosperma bracteatum (Hochst.) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254328-1

= Monechma bracteatum Hochst., Flora 24: 375 (Hochstetter 1841) = Justicia bracteata (Hochst.) Zarb (1879: 32). Type: Sudan, Kordofan, Tejara, 19 Nov. 1839, Kotschy 261 (holotype TUB; isotypes GOET* [GOET005559], GZU, HBG* [HBG502284, HBG502285], K! [K000378692], LD* [LD1226235], M* [M0109807], MPU, S* [S09-6163], STU* [STU000468], US* [US01049972]).

Monechma affine Hochst. (Hochstetter 1843: 76).

Monechma angustifolium Nees (1847: 412) = Justicia debilis (Forssk.) Vahl var. angustifolia (Nees) Oliv. (Oliver 1875: 129) = Monechma bracteatum Hochst. var. angustifolium (Nees) C.B.Clarke (1900: 215).

Justicia heterostegia T.Thoms. (in Speke 1863: 643).

Justicia blepharostegia E.Mey. ex T.Anderson (1863: 43).

Justicia ukambensis Lindau (1894: 69) = Monechma ukambense (Lindau) C.B.Clarke (1900: 220).

Monechma scabrinerve C.B.Clarke (1900: 215).

Monechma bracteatum Hochst. var. non-strobilifera C.B.Clarke (1900: 215).

DISTRIBUTION. Africa: Angola, Botswana, D. R. Congo, Eritrea, Ethiopia, Kenya, Malawi, Mozambique, Namibia, Somalia, South Africa, Sudan, Tanzania, Uganda, Zambia, Zimbabwe. Asia: India, Oman, Yemen.

NOTE. This species has often been treated within Monechma debile by previous authors; see Vollesen (2010, 2015) for a list of examples.

2. Meiosperma carnosum (Hedrén) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254329-1

= Justicia carnosa Hedrén, Willdenowia 36: 752 (2006a). Type: Somalia, Banaadir, 2 km from Muqdisho [Mogadishu] airport along road to Jasiira [Gezira], 4 May 1990, Thulin & Hedrén 7167 (holotype UPS; isotypes FT, K! [K000197085]).

DISTRIBUTION. Africa: Somalia.

3. ^ Meiosperma debile (Forssk.) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254330-1

= Dianthera debilis Forssk., Fl. Aegypt.-Arab.: 9 (Forsskål 1775) = Justicia debilis (Forssk.) Vahl (1791: 15) = Gendarussa debilis (Forssk.) Nees (1842: 302) = Monechma debile (Forssk.) Nees (1847: 411). Type: Yemen, “Tais”, Forsskål herb. 391 [microfiche 38: II. 3–4] (lectotype C* [C10013032], selected by Wood et al., Kew Bull. 83: 444 (1983)).

?Justicia somalensis Franch. (Franchet 1882: 53) — see note.

Justicia gregorii S.Moore (1894: 138).

Monechma bracteatum Hochst. var. hirsutior C.B.Clarke (1900: 215).

Monechma bracteatum Hochst. var. stricta C.B.Clarke (1900: 215).

Monechma troglodyticum Chiov. (Chiovenda 1942: 174).

DISTRIBUTION. Africa: Djibouti, Eritrea, Ethiopia, Kenya, Somalia, Sudan, Tanzania. Asia: Saudi Arabia, Yemen.

NOTE. Hedrén (2006b) tentatively placed Justicia somalensis Franch. as a synonym of this species but had not seen the type specimen.

4. ^ Meiosperma eminii (Lindau) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254331-1

= Justicia eminii Lindau, Bot. Jahrb. Syst. 20: 68 (1894). Type: Uganda, “Rubanga”, Mporroro, 20 April [listed as March in protologue] 1891, Stuhlmann 2086 (holotype B†; lectotype K! [K000378690], selected here).

Monechma bracteatum Hochst. var. eciliata C.B.Clarke (1900: 215) = M. debile (Forssk.) Nees var. eciliata (Forssk.) Chiov. (Chiovenda 1919: 161).

DISTRIBUTION. Africa: Burundi, D. R. Congo, Malawi, Rwanda, Tanzania, Uganda, Zambia.

NOTE. This species has been treated within Monechma debile by some authors; see Vollesen (2010) for examples.

5. ^ Meiosperma monechmoides (S.Moore) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254332-1

= Justicia monechmoides S.Moore, J. Bot. 18: 311 (1880) = Monechma monechmoides (S.Moore) Hutch. (Hutchinson 1946: 524). Type: Angola, Luanda, Imbondeiro dos Lobos, March 1858 [date fide Hiern 1900], Welwitsch 5140 (lectotype BM!, selected by Vollesen (2015: 214); isolectotypes K!, LISU* [LISU223491, LISU223493], P* [P00434925]).

Monechma welwitschii C.B.Clarke (1900: 216), nom. illegit.

Monechma tettense C.B.Clarke (1900: 216).

DISTRIBUTION. Africa: Angola, Botswana, Malawi, Mozambique, Namibia, South Africa, Zambia, Zimbabwe.

NOTES. The exact delimitation of this species and its relation to Meiosperma bracteatum requires further consideration. For example, there is a striking form of this species from northeast South Africa with notably large bracts and corollas (e.g. Codd 4233, Strey & Schlieben 8582, both K!) which may be distinct.

This species has been treated within Monechma debile by some authors, for example Munday (1995).

6. ^ Meiosperma tetrasperma (Hedrén) I.Darbysh. & E.Tripp comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254334-1

= Justicia tetrasperma Hedrén, Nordic J. Bot. 10: 151 (1990). Type: D. R. Congo, Shaba, Marungu, Vilain 60 (holotype BRLU).

DISTRIBUTION. Africa: D. R. Congo, Tanzania, Zambia.

Undescribed taxa of Meiosperma

^ Justicia sp. B of Vollesen (2015: 215).

DISTRIBUTION. Africa: Mozambique.

NOTE. An additional collection of this species has been made since the study of Vollesen (2015) by B. Wursten (BR) and it is confirmed to be an undescribed species (see Darbyshire et al. 2020, Fig. 1D); it is currently awaiting description.

Justicia sp. C of Vollesen (2015: 215).

DISTRIBUTION. Africa: Zambia.

Incompletely known taxa in Meiosperma

Monechma spissum C.B.Clarke (1900: 219). Type: Angola, Loanda, inter Teba et Quicuxe, March 1854, Welwitsch 5066 (holotype BM! [BM000923672]; isotype LISU* [LISU223494]).

DISTRIBUTION. Africa: Vollesen (2015) treated this name as a synonym of Justicia divaricata Licht. (= Pogonospermum divaricatum (Licht.) I.Darbysh. & Kiel), but the five-lobed calyx (fide Clarke 1900) does not fit with that species, and examination of the type specimen at BM reveals that the seeds of this species match those of Meiosperma. It may be a depauperate form of M. monechmoides but this requires further investigation. The isotype at LISU represents slightly better material than that at BM.

Pogonospermum Hochst. (Hochstetter 1844: 5). Type species: Pogonospermum ciliare (L.f.) Hochst. (Justicia ciliare L.f.), (lectotype selected by Pfeiffer 1874: 777) = P. ciliatum (Jacq.) I.Darbysh. & Kiel.

NOTE. Pfeiffer (1874) lectotypified Pogonospermum with P. ciliare by reference to “Justicia ciliaris Vahl”. Although Pfeiffer wrongly attributed that name to Vahl rather than to Linnaeus (1781), it seems highly likely that this error was based on reference to Hochstetter (1844) who also attributed J. ciliaris to Vahl — see discussion above. Pfeiffer’s lectotypification is therefore acceptable.

Pogonospermum sect. Pogonospermum

RECOGNITION. Erect annual herbs. Inflorescences of short or more elongate terminal spikes with bracts markedly to only slightly differentiated from the leaves; bracts, bracteoles and calyx lobes all conspicuously pale-ciliate. Calyx lobes with only the midvein prominent, margins pale-hyaline. Seeds oblate in face view, one side flattened, the other side convex and with a central ridge, with tufts of bristly multicellular trichomes at apex and on one side of hilum at base, the two tufts with trichomes orientated in opposite directions. Fig. 3A.

1. ^ Pogonospermum ciliatum (Jacq.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254446-1

= Justicia ciliata Jacq., Hort. Bot. Vindob. 2: 47, t. 104 (Jacquin 1772) = Dianthera ciliata (Jacq.) Medik. (Medikus 1783: 9) = Beloperone ciliata (Jacq.) Nees (1847: 422) = Monechma ciliatum (Jacq.) Milne-Redh. (Milne-Redhead 1934: 304). Type: Illustr. t.104 in Hort. Bot. Vindob. 2 (1774), from plant cult. in Vienna.

Justicia ciliaris L.f. (Linnaeus 1781: 84), nom. illegit. = Pogonospermum ciliare (L.f.) Hochst. (Hochstetter 1844: 6) = Schwabea ciliaris (L.f.) Nees (1847: 384).

Monechma hispidum Hochst. (Hochstetter 1841: 375) = Pogonospermum hispidum (Hochst.) Hochst. (Hochstetter 1844: 6).

Schwabea spicigera Nees (1847: 384).

Schwabea spicigera Nees var. β luxurians Nees (1847: 384).

Hygrophila lutea T.Anderson (1863: 22).

Ecbolium setaceum Kuntze (1891: 979) = Dianthera setacea (Kuntze) Voss (in Siebert & Voss 1896: 809).

Justicia buettneri Lindau (1894: 68).

Justicia togoensis Lindau (1894: 72).

DISTRIBUTION. Africa: Benin, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, D. R. Congo, Gambia, Ghana, Guinea, Guinea Bissau, Ethiopia, Ivory Coast, Malawi, Mali, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, South Sudan, Sudan, Tanzania, Togo, Uganda, Zambia.

Pogonospermum sect. Savannicola I.Darbysh. & Kiel sect. nov. Type species: Pogonospermum scabridum (S.Moore) I.Darbysh. & Kiel.

http://www.ipni.org/urn:lsid:ipni.org:names:77254447-1

RECOGNITION. Perennial herbs with a ± woody base and rootstock. Inflorescences of terminal spikes, sometimes also with additional spikes in the distalmost leaf axils; bracts markedly differentiated from the leaves, linear, lanceolate, to narrowly elliptic, oblong or oblanceolate; bracts and bracteoles, single-veined or sometimes with the two lateral veins also prominent, margins sometimes markedly paler than rest of surface. Calyx lobes with only the midvein prominent, sometimes with two parallel lateral veins also more faintly visible, margin often pale-hyaline. Seeds ± oblate in face view, one side flattened, the other side convex and with a central ridge, at first white sericeous-puberulous, these trichomes sometimes sparse or absent on mature seeds. Fig. 3B.

2. ^ Pogonospermum attenuifolium (Vollesen) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254448-1

= Justicia attenuifolia Vollesen, Fl. Trop. E. Africa, Acanth.: 599 (2010). Type: Tanzania, Tunduru Distr., 95 km on Masasi-Tunduru road, 19 March 1963, Richards 17968 (holotype K! [K000794980]).

DISTRIBUTION. Africa: Mozambique, Tanzania.

3. ^ Pogonospermum depauperatum (T.Anderson) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254449-1

= Justicia depauperata T.Anderson, J. Proc. Linn. Soc., Bot. 7: 40 (1863) = Ecbolium depauperatum (T.Anderson) Kuntze (1891: 980) = Monechma depauperatum (T.Anderson) C.B.Clarke (1900: 217). Type: Nigeria, “Onitsha”, without date, Barter 592 [no. not listed in protologue] (lectotype K! [K000378699], selected here). Additional syntype: Nigeria, “Onitsha”, without date, Barter 1300 [no. not listed in protologue] (K! [K000378701]).

Justicia barteri T.Anderson (1863: 39) = Ecbolium barteri (T.Anderson) Kuntze (1891: 979).

Justicia sexsulcata Lindau (1894: 67).

Nicoteba marginata Lindau (1895: 119) = Monechma marginatum (Lindau) C.B.Clarke (1900: 217).

DISTRIBUTION. Africa: Benin, Cameroon, Central African Republic, D. R. Congo, Ghana, Guinea, Ivory Coast, Mali, Nigeria, Senegal, Sierra Leone, South Sudan, Togo.

4. ^ Pogonospermum ndellense (Lindau) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254450-1

= Justicia ndellensis Lindau, Mém. Soc. Bot. France 8: 52 (1908) = Monechma ndellense (Lindau) J.Miège & Heine (1962: 121). Type: Central African Republic, Dar-Banda oriental, Ndellé, 15 – 20 Dec. 1902, Chevalier 6878 (lectotype P* [P00434927], selected here; isolectotypes K! [K000378694], P* [P00434928]).

DISTRIBUTION. Africa: Burkina Faso, Central African Republic, Ghana, Guinea, Mali, Senegal, Sudan, Togo.

NOTE. When transferring this species to Monechma, Miège & Heine (1962) noted that it shows considerable variation across its range and that two taxa may be involved. Some particularly striking populations from sandstone outcrops in central Ghana (e.g. Lock & Hall in GC 44357, GC!, K!) are noteworthy and are currently under investigation as a potentially new species (I. Darbyshire & G. Ameka, unpubl. data).

5. ^ Pogonospermum scabridum (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254451-1

= Justicia scabrida S.Moore, J. Bot. 18: 310 (1880) = Monechma scabridum (S.Moore) C.B.Clarke (1900: 217). Type: Angola, Pungo Andongo, 11 March 1857, Welwitsch 5092 (lectotype BM! [BM000923677], selected by Vollesen (2015: 222); isolectotypes K! [K000378724], LISU* [LISU223487]).

Justicia marginata Lindau (1894: 73).

DISTRIBUTION. Africa: Angola, D. R. Congo, Zambia.

6. ^ Pogonospermum subsessile (Oliv.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254452-1

= Justicia subsessilis Oliv., Trans. Linn. Soc. London 29: 129, t.129b (Oliver 1875) = Monechma subsessile (Oliv.) C.B.Clarke (1900: 216). Type: Tanzania, Bukoba Prov., Karagwe, 2 Dec. 1861, Speke & Grant 213 (holotype K! [K000378735]).

Justicia simplicispica C.B.Clarke (1900: 188).

Monechma nemoralis S.Moore (1909: 296).

DISTRIBUTION. Africa: Angola, Burundi, D. R. Congo, Kenya, Rwanda, Tanzania, Uganda, Zambia, Zimbabwe.

Pogonospermum sect. Virgultorum I.Darbysh. & Kiel sect. nov. Type species: Pogonospermum virgultorum (S.Moore) I.Darbysh. & Kiel.

http://www.ipni.org/urn:lsid:ipni.org:names:77254453-1

RECOGNITION. Perennial herbs or shrublets with a woody base and rootstock. Inflorescences terminal or mixed axillary and terminal spikes or pedunculate axillary fascicles; bracts markedly differentiated from the leaves, small, linear, lanceolate or proximal pairs elliptic or obovate. Calyx lobes with only the midvein prominent, the two parallel lateral veins inconspicuous or not visible. Seeds ± globose in face view, only slightly flattened, glabrous. Fig. 3C.

7. ^ Pogonospermum fanshawei (Vollesen) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254454-1

= Justicia fanshawei Vollesen, Fl. Zamb. 8 (6): 220 (2015). Type: Zambia, Mansa (Fort Rosebery) Distr., 5 May 1964, Fanshawe 8576 (holotype K! [K000918638]; isotype NDO).

DISTRIBUTION. Africa: Zambia.

NOTE. This species is unusual in Pogonospermum in having small pedunculate fascicles of flowers, sometimes restricted to the distal leaf axils, but in some cases the inflorescence becomes slightly more elongate and secund-spiciform as in P. virgultorum.

8. ^ Pogonospermum virgultorum (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254455-1

= Monechma virgultorum S.Moore, J. Bot. 49: 311 (1911) = Justicia virgultorum (S.Moore) I.Darbysh. & Goyder (Darbyshire & Goyder 2019: 106). Type: Angola, Cuando Cubango, Cassuango, Cuiriri, 26 March 1906, Gossweiler 3679 (holotype BM! [BM000923667]).

Monechma carrissoi Benoist (1950: 30).

DISTRIBUTION. Africa: Angola.

Pogonospermum sect. Tricostatum I.Darbysh. & Kiel sect. nov. Type species: Pogonospermum tricostatum (Vollesen) I.Darbysh. & Kiel.

http://www.ipni.org/urn:lsid:ipni.org:names:77254456-1

RECOGNITION. Perennial herbs with a ± woody base and rootstock. Inflorescences of terminal spikes, sometimes also with additional spikes in the distalmost leaf axils; bracts markedly differentiated from the leaves, linear or lanceolate to narrowly oblanceolate. Calyx lobes (and usually also bracts and bracteoles) with three veins prominent and often also differently coloured to the paler intercostal surface. Seeds ± globose in face view, only slightly flattened, glabrous. Fig. 3D.

9. ^ Pogonospermum cubangense (I.Darbysh. & Goyder) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254457-1

= Justicia cubangensis I.Darbysh. & Goyder, Blumea 64: 100 (2019). Type: Angola, Cuando Cubango Province, Cuchi River Gorge (Cubango drainage), c. 7 km N of Cuchi, 28 May 2015, Goyder 8068 (holotype K! [K001333210]; isotypes CAS!, INBAC, LUBA).

DISTRIBUTION. Africa: Angola.

10. Pogonospermum eriniae (I.Darbysh.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254458-1

= Justicia eriniae I.Darbysh., Blumea 64: 101 (in Darbyshire & Goyder 2019). Type: Angola, Namibe Prov., between Bibala and Assunçao, 10 April 2017, Tripp & Dexter 6917 (holotype K! [K001322688]; isotypes COLO!, LUBA!).

DISTRIBUTION. Africa: Angola.

11. Pogonospermum glaucifolium (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254459-1

= Monechma glaucifolium S.Moore, J. Bot. 49: 310 (1911) = Justicia glaucifolia (S.Moore) I.Darbysh. & Goyder (Darbyshire & Goyder 2019: 105). Type: Angola, without precise locality or date, Gossweiler s.n. (holotype BM! [BM000923665]).

DISTRIBUTION. Africa: Angola.

12. Pogonospermum lolioides (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254460-1

= Justicia lolioides S.Moore, J. Bot. 18: 310 (1880) = Monechma lolioides (S.Moore) C.B.Clarke (1900: 218). Type: Angola, Malange, Distr. Pungo Andongo, de Mata de Mutollo, Jan. 1857, Welwitsch 5178 (lectotype BM! [BM000923676], selected by Darbyshire & Goyder (2019: 105); isolectotypes C* [C10000041], K! [K000378722], LD* [LD1569502], LISU* [LISU223483]).

12a. Pogonospermum lolioides (S.Moore) I.Darbysh. & Kiel var. lolioides

DISTRIBUTION. Africa: Angola.

12b. Pogonospermum lolioides (S.Moore) I.Darbysh. & Kiel var. latifolium (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254462-1

= Justicia lolioides S.Moore var. latifolia S.Moore, J. Bot. 18: 310 (1880). Type: Angola, Malange, Distr. Pungo Andongo, inter Quisonde et Condo, March 1857, Welwitsch 5099 (lectotype BM! [BM000923675], selected by Darbyshire & Goyder (2019: 105); isolectotypes C* [C10000039], K! [K000378723], LD* [LD1575500]).

DISTRIBUTION. Africa: Angola.

13. Pogonospermum laetum (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254463-1

= Justicia laeta S.Moore, J. Bot. 18: 311 (1880). Type: Angola, Pungo Andongo, inter Condo et Quisonde, March 1857, Welwitsch 5108 (lectotype BM! [BM000839214], selected by Darbyshire & Goyder (2019: 105); isolectotype K! [K000419259]).

DISTRIBUTION. Africa: Angola.

NOTE. This species is placed tentatively in Pogonospermum sect. Tricostatum based on the spiciform inflorescences and 3-veined calyx lobes, but molecular evidence is needed to confirm this; see Darbyshire & Goyder (2019) for further discussion on its placement.

14. ^ Pogonospermum rigidum (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254464-1

= Monechma rigidum S.Moore, J. Bot. 49: 310 (1911). Type: Angola, Menongue [Munongue], April 1906, Gossweiler 3355 (lectotype BM! [BM00092362], selected by Darbyshire & Goyder (2019: 106); isolectotype K! [K001009703]).

Justicia moorei I.Darbysh. & Goyder (Darbyshire & Goyder 2019: 106).

DISTRIBUTION. Africa: Angola.

15. ^ Pogonospermum tricostatum (Vollesen) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254465-1

= Justicia tricostata Vollesen, Fl. Trop. E. Africa, Acanth.: 598 (2010). Type: Tanzania, Sumbawanga Distr., Tatanda Mission, 24 Feb. 1994, Bidgood et al. 2431 (holotype K! [K000794981]; isotypes BR* [BR0000005737499], DSM, EA, K! [K000794982], MO, NHT, P, WAG).

DISTRIBUTION. Africa: Tanzania, Zambia.

Pogonospermum sect. Serotinum I.Darbysh. & Kiel sect. nov. Type species: Pogonospermum serotinum (P.G.Mey.) I.Darbysh. & Kiel.

http://www.ipni.org/urn:lsid:ipni.org:names:77254466-1

RECOGNITION. Shrublet with dense branching, mature branches woody; leaves with lateral veins prominent and arching strongly towards apex, often leaves appearing tripliveined. Inflorescences of lax terminal spikes; bracts (at least distally) markedly differentiated from the leaves, narrowly elliptic or lanceolate. Calyx lobes with only midvein prominent. Seeds compressed, one side ± flat, the other side convex, glabrous. Fig. 3E.

16. ^ Pogonospermum serotinum (P.G.Mey.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254468-1

= Monechma serotinum P.G.Mey., Mitt. Bot. Staatssamml. München 11: 112 (Meyer 1973) = Justicia serotina (P.G.Mey.) J.C.Manning & Goldblatt (2014: 46). Type: Namibia, Kaokoveld, zwischen Etengua und Otjitanda, 5 July 1969, Meyer 1245 (holotype M* [M0109802]; isotypes M* [M0109803], PRE, WIND! [WIND000032567]).

DISTRIBUTION. Africa: Namibia.

Pogonospermum sect. Aridicola I.Darbysh. & Kiel sect. nov. Type species: Pogonospermum cleomoides (S.Moore) I.Darbysh. & Kiel.

http://www.ipni.org/urn:lsid:ipni.org:names:77254467-1

RECOGNITION. Shrublets, perennial herbs or more rarely annual herbs, often with intricate branching, mature branches sometimes woody and gnarled, foliage often dense. Inflorescences of axillary single-flowered cymes, bracts undifferentiated from the leaves or only slightly differentiated, flowers sometimes together forming a poorly defined, leafy terminal spike. Calyx lobes with only midvein prominent or with no veins prominent, margins sometimes hyaline. Seeds rounded or ovate in face view, one side flat or concave to slightly convex, the other side more markedly convex and usually with a central ridge, sometimes mottled or intricately patterned, glabrous. Fig. 3F & G.

17. ^ Pogonospermum australe (P.G.Mey.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254469-1

= Monechma australe P.G.Mey., Mitt. Bot. Staatssamml. München 3: 602 (1960) = Monechma genistifolium (Engl.) C.B.Clarke subsp. australe (P.G.Mey.) Munday (1995: 54) = Justicia genistifolia Engl. subsp. australis (P.G.Mey.) J.C.Manning & Goldblatt (2014: 46) = Justicia australis (P.G.Mey.) Vollesen (2015: 219). Type: Namibia, Distr. Gibeon, Farm Haribes [Harabies], 7 April 1956, Volk 12244 (holotype M* [M-0109813]).

DISTRIBUTION. Africa: Namibia, South Africa.

18. ^ Pogonospermum calcaratum (Schinz) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254470-1

= Monechma calcaratum Schinz, Vierteljahrsschr. Naturf. Ges. Zürich 61: 441 (1916). Type: Namibia, Gross Namaland, Anab R., 5 Sept. 1897, Dinter 1060 (holotype Z* [Z-000030966]).

Justicia namibensis J.C.Manning & Goldblatt (2014: 46).

DISTRIBUTION. Africa: Namibia.

19. Pogonospermum callothamnum (Munday) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254471-1

= Monechma callothamnum Munday, S. African J. Bot. 53: 140 (1987) = Justicia callothamnum (Munday) J.C.Manning & Goldblatt (2014: 46). Type: Namibia, Bethanie Distr., Zaracheibis, 27 Sept. 1972, Merxmüller & Giess 28867 (holotype PRE* [PRE0141079-0]; isotypes M* [M-0109810], WIND! [WIND000072662]).

DISTRIBUTION. Africa: Namibia.

20. ^ Pogonospermum cleomoides (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254472-1

= Justicia cleomoides S.Moore, J. Bot. 18: 313 (1880) = Monechma cleomoides (S.Moore) C.B.Clarke (1900: 220). Type: Angola, “inter Mossamedes et Cavalheiros”, July 1859, Welwitsch 5006 (lectotype BM! [BM000923669], selected here; isolectotypes C* [C10000038], K! [K000378715], LD* [LD1684006], LISU* [LISU223503], P* [P00434923]).

Justicia arenicola Engl. (Engler 1888: 264) = Ecbolium arenicola (Engl.) Kuntze (1891: 980) = Monechma arenicola (Engl.) C.B.Clarke (1900: 288).

Monechma tonsum P.G.Mey. (Meyer 1957: 304). = Justicia tonsa (P.G.Mey.) J.C.Manning & Goldblatt (2014: 46), synon. nov.

DISTRIBUTION. Africa: Angola, Namibia.

NOTE. Monechma tonsum is included in the synonymy of P. cleomoides in light of the findings in Darbyshire et al. (2020); see discussion in that publication.

21. Pogonospermum crassiusculum (P.G.Mey.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254473-1

= Monechma crassiusculum P.G.Mey., Mitt. Bot. Staatssamml. München 3: 604 (Meyer 1960) = Justicia crassiuscula (P.G.Mey.) J.C.Manning & Goldblatt (2014: 46). Type: Namibia, Kahanstal, Dec. 1934, Dinter 8141 (holotype M* [M0109808]; isotypes HBG* [HBG502290], K! [K000378766], M* [M0109809], PRE* [PRE0143449-0], S* [S09-6183], WIND! [WIND000032315], Z).

DISTRIBUTION. Africa: Namibia.

22. ^ Pogonospermum desertorum (Engl.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254474-1

= Justicia desertorum Engl., Bot. Jahrb. Syst. 10: 263 (Engler 1888) = Ecbolium desertorum (Engl.) Kuntze (1891: 980) = Monechma desertorum (Engl.) C.B.Clarke (1900: 218). Type: Namibia, Husab, June 1886, Marloth 1462 (holotype B†; isotypes BOL, GH* [GH00217460], GRA* [GRA0002787-0], K! [K000378771], PRE* [PRE0143451-0, PRE0593969-0]).

DISTRIBUTION. Africa: Namibia.

23. ^ Pogonospermum divaricatum (Licht.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254475-1

= Justicia divaricata Licht. in Roem. & Schult., Syst. Veg. ed. 15, 1: 163 (Roemer & Schultes 1817). Type: South Africa, Grootrivierspoort, without date, Lichtenstein s.n. [Herb. Willdenow no. 355] (holotype B* [B-W 00355 -01 0]).

Gendarussa incana Nees var. villosa Nees (1841: 368).

Adhatoda capensis (Thunb.) Nees var. arenosa Nees (1847: 391).

Adhatoda divaricata Nees (1847: 391) = Justicia divaricata (Nees) T.Anderson (1863: 42) = Monechma divaricatum (Nees) C.B.Clarke (1901: 72).

Justicia mossamedea S.Moore (1880: 312).

Justicia nepeta S.Moore (1880: 312) = Monechma nepetum (S.Moore) C.B.Clarke (1900: 219).

Justicia namaensis Schinz (1890: 202) = Monechma namaense (Schinz) C.B.Clarke (1901: 73).

Ecbolium villosum Kuntze (1891: 978).

Monechma floridum C.B.Clarke (1900: 219).

Monechma fimbriatum C.B.Clarke (1901: 72).

Monechma nepetoides C.B.Clarke (1901: 73).

Monechma angustissimum S.Moore (1903: 137).

Monechma eremum S.Moore (1907: 231).

Monechma terminale S.Moore (1908: 75).

Monechma quintasii Benoist (1950: 37), synon. nov.

DISTRIBUTION. Africa: Angola, Botswana, Eswatini, Mozambique, Namibia, South Africa, Zambia, Zimbabwe.

NOTE. The multiple synonyms reflect the considerable variation within this widespread species, but it was found to be monophyletic in the RADseq study of Darbyshire et al. (2020).

24. Pogonospermum distichotrichum (Lindau) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254476-1

= Justicia distichotricha Lindau, Bot. Jahrb. Syst. 43: 357 (1909) = Monechma distichotrichum (Lindau) P.G.Mey. (Meyer 1961: 66). Type: Namibia, Knibis [Kuibis] R., July 1907, Range 380 (holotype B†; isotypes BOL, SAM).

DISTRIBUTION. Africa: Namibia, South Africa.

25. ^ Pogonospermum genistifolium (Engl.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254477-1

= Justicia genistifolia Engl., Bot. Jahrb. Syst. 10: 264 (Engler 1888) = Ecbolium genistifolium (Engl.) Kuntze (1891: 487) = Monechma genistifolium (Engl.) C.B.Clarke (1900: 218). Type: Namibia, Karibib, May 1886, Marloth 1424 (holotype B†; isotypes BOL, GRA* [GRA0002785-0], K! [K000378765], M* [M0109804], SAM* [SAM0042885-0]).

Justicia hereroensis Engl. (Engler 1888: 264) = Ecbolium hereroense (Engl.) Kuntze (1891: 980) = Monechma hereroense (Engl.) C.B.Clarke (1900: 220).

DISTRIBUTION. Africa: Namibia.

26. ^ Pogonospermum grandiflorum (Schinz) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254478-1

= Monechma grandiflorum Schinz, Vierteljahrsschr. Naturf. Ges. Zürich 61: 442 (1916). Type: Namibia, Gross Namaland, [south of] Rehoboth, 1891, Fleck 537 (lectotype Z* [Z-000000101] selected here; isolectotype Z* [Z-000000102]).

Justicia fleckii J.C.Manning & Goldblatt (2014: 46).

DISTRIBUTION. Africa: Namibia.

27. ^ Pogonospermum incanum (Nees) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254479-1

= Gendarussa incana Nees, Linnaea 15: 367 (1841) excl. var. villosa = Adhatoda incana (Nees) Nees (1847: 393) = Justicia incana (Nees) T.Anderson (1863: 42) = Ecbolium incanum (Nees) Kuntze (1891: 980) = Monechma incanum (Nees) C.B.Clarke (1901: 69). Type: South Africa, Nieuweveld, Drège s.n. (lectotype K!, selected by Vollesen (2015: 219), see note). Additional syntype: South Africa, “circa Graaff-Reinet; in Karro [Karoo], prope castellum Beaufort”, Ecklon 280 (BOL).

DISTRIBUTION. Africa: Botswana, Namibia, South Africa.

NOTE. When lectotypifying Gendarussa incana, Vollesen (2015) referred to the collecting locality for the Drège lectotype as “between Beaufort West and Rhinoster Kop”. This locality information was added to the sheet by Charles Baron Clarke; the original specimen cites only “Cape, Drège” and the protologue gives the collecting locality as “Nieuweveld”.

28. ^ Pogonospermum leucoderme (Schinz) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254480-1

= Justicia leucodermis Schinz, Verh. Bot. Vereins Prov. Brandenburg 31: 202 (1890) = Monechma leucoderme (Schinz) C.B.Clarke (1901: 70). Type: Namibia, Gross Namaland, zwischen Tiras und Rehoboth, 1885, Schinz 85 [no. not listed in protologue] (lectotype Z* [Z000030986], selected here; ?isolectotype K! [K000378707], labelled as Schinz 1). Additional syntype: Namibia, Tsirub-Gebirge, 1884, Schinz 84 [no. not listed in protologue] (Z* [Z000075019], ZT* [ZT00009912]; K! [K000378708], labelled as Schinz 29).

DISTRIBUTION. Africa: Namibia.

29. ^ Pogonospermum mollissimum (Nees) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254481-1

= Adhatoda mollissima Nees in de Candolle, Prodr. 11: 391 (1847) = Monechma mollissimum (Nees) P.G.Mey. (Meyer 1957: 304). Type: South Africa, 1837, Drège s.n. (lectotype K! [K000378762], selected here; isolectotypes K! [K000378763], PRE).

Monechma molle E. Mey. ex C.B.Clarke (1901: 69).

Justicia dregei J.C.Manning & Goldblatt (2014: 46).

DISTRIBUTION. Africa: Namibia, South Africa.

NOTE. The two type specimens at K are mounted on the same sheet; K000378762 derives from Hooker’s herbarium whilst K000378763 is from Bentham’s herbarium. As Nees states that he saw the collection in Hooker’s herbarium, the former is here selected as lectotype. Additional collecting locality information, believed to have been added at a later date by Charles Baron Clarke, is noted on both the Kew specimens: “between Holgat River and the Orange River. [alt.] 1000 – 1500 ft. Little Namaqualand”. Nees also saw a duplicate in “h. Drèg[e]” that is here assumed to have been in Berlin and was likely to have been destroyed during World War II.

30. ^ Pogonospermum patulum (Licht.) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254482-1

= Justicia patula Licht. in Roem. & Schult., Syst. Veg., ed. 15 bis 1: 164 (Roemer & Schultes 1817) = Gendarussa patula (Licht.) Nees (1841: 367) = Adhatoda patula (Licht.) Nees (1847: 393) = Ecbolium patulum (Licht.) Kuntze (1891: 981). Type: South Africa, “in collibus trans fluvium tkai garieb [Orange River] prope vadum incolis Priskab [Prieska] dictum, ad promont. B. Spei”, without date, Lichtenstein s.n. (holotype B* [B-W 00357-01 0]).

Justicia spartioides T.Anderson (1863: 43) = Ecbolium spartioides (T.Anderson) Kuntze (1891: 981) = Monechma spartioides (T.Anderson) C.B.Clarke (1901: 72), synon. nov.

Justicia atherstonei T.Anderson (1863: 42) = Ecbolium atherstonei (T.Anderson) Kuntze (1891: 980) = Monechma atherstonei (T.Anderson) C.B.Clarke (1901: 72), synon. nov.

Monechma pseudopatulum C.B.Clarke (1901: 70), synon. nov.

Monechma pseudopatulum C.B.Clarke var. latifolium C.B.Clarke (1901: 70), synon. nov.

DISTRIBUTION. Africa: Namibia, South Africa.

NOTE. This species is well known as Monechma spartioides (see e.g. Munday 1995), but the earliest validly published name for this species is Justicia patula Licht. in Roemer & Schultes (1817).

31. Pogonospermum robustum (Bond) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254483-1

= Monechma robustum Bond, J. S. African Bot. 6: 67 (in Compton & Bond 1940). Type: South Africa, Western Cape, Ladismith Distr., Wittespoort, 12 Sept. 1938, Compton 7350 (holotype NBG* [NBG0048649-0]; isotypes BOL, PRE* [PRE0145884-0]).

Justicia karroica J.C.Manning & Goldblatt (2014: 46).

DISTRIBUTION. Africa: South Africa.

32. ^ Pogonospermum salsola (S.Moore) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254484-1

= Justicia salsola S.Moore, J. Bot. 18: 340 (1880) = Monechma salsola (S.Moore) C.B.Clarke (1900: 220). Type: Angola, Mossamedes, Praia da Amelia, July 1859, Welwitsch 5023 (lectotype BM* [BM 000923670], selected here; isolectotypes K! [K000378716], P* [P00434932]).

DISTRIBUTION. Africa: Angola, Namibia.

33. Pogonospermum saxatile (Munday) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254485-1

= Monechma saxatile Munday, S. African J. Bot. 3: 363 (1984) = Justicia saxatilis (Munday) J.C.Manning & Goldblatt (2014: 46). Type: South Africa, Northern Cape, about 8 km N of Pofadder, 16 June 1948, Acocks 14394 (holotype PRE; isotype K! [K000378761]).

DISTRIBUTION. Africa: South Africa.

Pogonospermum incertae sedis

34. Pogonospermum kasamae (Vollesen) I.Darbysh. & Kiel comb. nov.

http://www.ipni.org/urn:lsid:ipni.org:names:77254486-1

= Justicia kasamae Vollesen, Fl. Zamb. 8 (6): 222 (2015). Type: Zambia, Kasama, 1 July 1964, Fanshawe 8774 (holotype K! [K000743643]; isotype NDO).

DISTRIBUTION. Africa: Zambia.

NOTE. In the protologue for this species, Vollesen (2015) records the seeds as “mottled grey and black, c. 3.5 × 4 mm, whitish sericeous or densely so on edges, sparser on flanks, glabrescent” (p. 223). This would place this species in sect. Savannicola. However, our observations on the K material of this species have found the seeds to be glabrous, even when immature. The broad, elliptic or obovate bracts in this species are unusual in the genus, and its infrageneric placement is uncertain at present.

Undescribed species of Pogonospermum

Pogonospermum sp. aff. ndellense (see note under P. ndellense, sp. 4 above).

DISTRIBUTION. Africa: Ghana.

Justicia sp. H of Vollesen (2010: 598).

DISTRIBUTION. Africa: Tanzania.

NOTE. This species is known only from a single flowering collection, Leedal 4092 (K!) from Umalila District in southern Tanzania. Although Vollesen (2010) compared this species to Justicia varians (C.B.Clarke) Vollesen which is now placed in Justicia sect. Tyloglossa (Hochst.) Lindau (see below), the prominently 3-veined bracts, bracteoles and calyx lobes suggest affinity with Pogonospermum sect. Tricostatum and the leaf venation is also reminiscent of some species in this section. Further material, including fruits, is required to confirm this placement.

Excluded taxa

Monechma acutum C.B.Clarke (1901: 71) = Justicia acuta (C.B.Clarke) Fourc. (Fourcade 1941: 6).

NOTE. The type specimens at Kew, Burchell 4761, 4785 (together on the same sheet) have been annotated by P. G. Meyer in 1959 as “Justicia, near J. orchidoides L. f.”; we concur with this placement.

Monechma clarkei Schinz (1916: 440) = Justicia guerkeana Schinz (1890: 201).

NOTE. Justicia guerkeana Schinz is morphologically close to J. platysepala (see below) and does not belong within either Meiosperma or Pogonospermum. Amongst other differences, it has densely tuberculate seeds.

Monechma foliosum C.B.Clarke (1901: 73).

NOTE. The original material of this species includes three specimens, one of which (Bolus 1873, K000378767) is a mixed collection consisting of Pogonospermum patulum plus a species of Justicia. The most informative of the three syntypes, Bolus 2422 (K000378768) closely resembles Justicia cuneata Vahl and may be of that species.

Monechma linaria (T.Anderson) C.B.Clarke (1901: 70) = Justicia linaria T.Anderson (1863: 42).

NOTE. The type specimen (Drège s.n., K) is depauperate and lacks fruits, but P. G. Meyer in 1959 annotated it as “probably Justicia near orchidoides L.f.” and we concur with this conclusion.

Monechma pilosella Nees (1847: 412) = Justicia pilosella (Nees) Hilsenb. (Hilsenbeck 1990: 225).

NOTE. This neotropical species is not morphologically close to either of the paleotropical genera Meiosperma or Pogonospermum.

Monechma platysepalum S.Moore (1907: 231) = Justicia platysepala (S.Moore) P.G.Mey. (Meyer 1956: 170).

NOTE. Justicia platysepala is morphologically similar to J. guerkeana (see note to M. clarkei above) and the RADseq phylogeny of Darbyshire et al. (2020) confirms that J. platysepala is not allied to either Meiosperma or Pogonospermum.

Monechma praecox Milne-Redh. (Milne-Redhead 1937: 430) = Justicia bequaertii De Wild. (De Wildeman 1914: 429).

NOTE. This name is treated as a synonym of Justicia bequaertii De Wild. (see Champluvier 2013; Vollesen 2015). Milne-Redhead (1937) considered this species to be intermediate between Monechma and Justicia as it has a 2-seeded capsule but with sculptured seeds. However, the seed sculpturing together with the long-stipitate capsule with rounded fertile portion place this outside of either Meiosperma or Pogonospermum.

Monechma varians C.B.Clarke (1900: 216) = Justicia varians (C.B.Clarke) Vollesen (2015: 221).

NOTE. This species was placed outside of the two “Monechma” clades in the RADseq phylogeny of Darbyshire et al. (2020) and is now considered to be allied to Justicia linearispica C.B.Clarke in the Tyloglossa clade of Justicia (Darbyshire et al. 2020).

Monechma violaceum (Vahl) Nees (1847: 411) = Megalochlamys violacea (Vahl) Vollesen (1989: 608).

NOTE. This species is a member of the genus Megalochlamys in the Tetramerium lineage of Acanthaceae (McDade et al. 2018).