A revision of the African genus Mesanthemum (Eriocaulaceae)

Mesanthemum is a genus comprising 16 species in the family Eriocaulaceae and is native to Africa and Madagascar. Eriocaulaceae are characterised by a basal tuft or rosette of narrow leaves and small flowers in heads. Mesanthemum can be recognised by diplostemonous flowers and fused glandular pistillate petals. While most Mesanthemum species are large perennial herbs, two small ephemeral species from West Africa, M. albidum and M. auratum differ from the rest of the genus by their shorter life cycle, smaller size, simpler floral structures and different seed surface patterning. A molecular phylogenetic study, morphological comparisons and scanning electron microscope (SEM) examination of seed coat sculpture were carried out to determine whether they should be separated as a new genus. The molecular results indicate that the two ephemeral species are nested in the Mesanthemum clade. However, they are not closely related to each other. All species of Mesanthemum are here revised, including the description of a new species M. alenicola from Equatorial Guinea. An identification key is provided, together with taxonomic descriptions, synonymy and notes. Images of the seeds as seen under SEM are provided where available. Lectotypifications are provided for Mesanthemum albidum, M. bennae, M. pilosum, M. prescottianum, M. pubescens and M. variabile. A neotype is selected for M. rutenbergianum, which is synonymised with M. pubescens.


Introduction
Mesanthemum Körn. belongs to the pantropical and warm temperate monocot family Eriocaulaceae, comprising ten genera and c. 1200 species (WCSP 2018). Most of the generic diversity occurs in South America, especially Brazil (Giulietti et al. 1995;Dokkedal et al. 2008), and the type genus Eriocaulon L. is pantropical, extending into warm temperate parts of Asia, Australia, North America and western Europe. Mesanthemum is unusual in being confined to tropical Africa and Madagascar. It has been little studied from a molecular phylogenetic point of view (Andrade et al. 2010), most previous work being associated with African Flora accounts (e.g. Phillips 1997Phillips , 2010Phillips , 2011Phillips , 2016. The family is characteristically found in permanently or seasonally wet habitats on a variety of substrates (Stützel 1998: 203), often favouring sandy soils. A few species, including M. reductum H.E.Hess, are true aquatics, occurring in rivers and lakes.
Mesanthemum was last revised by , who recognised 10 species. Since then, new material has been collected, and several new species have been described (Hess 1955;Kimpouni 1994;Moldenke 1949) bringing the total to 16 accepted species (WCSP 2018). The genus is morphologically well defined, most species being robust perennials with scapes up to c. 60 cm high arising from a basal rosette of linear or linear-lanceolate leaves sometimes up to 50 cm long. These species are easily distinguished from most Eriocaulon in Africa by their more robust habit and often hairy leaves and scapes (see e.g. Mesanthemum africanum Moldenke in Fig. 1). The tiny unisexual flowers are gathered into dense heads (capitula) which are solitary on the scapes, the whitehairy flowers being supported below by an involucre of several series of usually tough, involucral bracts (Fig. 2). Sometimes, the innermost involucral bracts greatly exceed the floral disc. The flowers have six stamens and glandular petals as in Eriocaulon, but the petals of the female flowers are connate into a tube above the ovary, not free as in Eriocaulon. The seed surface structure is uniform between the perennial species, as discussed below.
Two slender ephemeral species from West Africa, Mesanthemum albidum Lecomte (Fig. 3A, B) and M. auratum Lecomte (Fig. 3C, D), do not conform to the general pattern set out above. Apart from their smaller short-lived habit, they have completely different seed surface structures compared to the perennial species. Therefore, the question arose as to whether these two species should be removed from Mesanthemum and placed in a separate genus. A molecular phylogenetic study was carried out to explore relationships within the genus, and especially to determine whether the two ephemerals are congeneric with the perennial Mesanthemum species. This paper revises all known Mesanthemum species with updated descriptions, nomenclature, typifications, distribution and habitat notes. A new species to science is described from Equatorial Guinea.

Molecular study
For Mesanthemum albidum, M. auratum, M. prescottianum (Bong.) Körn. and M. tuberosum Lecomte, total genomic DNA was extracted from silica-gel-dried leaf materials. For M. bennae Jacq.-Fél., leaves for DNA extraction were taken from two recently-collected herbarium specimens, van der Burgt 2185 and Konomou 311. Additional species of Mesanthemum, and of two other Eriocaulaceae genera Eriocaulon and Syngonanthus were included using existing sequence data (Y. Ito et al. unpublished data). All sampling information is provided in Table 1. CTAB procedure following Doyle & Doyle (1987) was applied  for DNA extraction. Four plastid regions matK, rbcL, rpoB and rpoC1, and the nuclear region PHYC were amplified by polymerase chain reactions (PCR) with PCR Premix 'DreamTaq' Mix in a total volume of 25 μL. Sequences of primer pairs used and the PCR profiles are presented in Table 2 and Table 3, respectively.
Amplified fragments were examined with 1% agarose gel electrophoresis and purified with Macherey-Nagel Gel and PCR Clean-up Columns. To separate the forward and reverse chains, cyclesequencing using BigDye™ Terminator v.3.1 Cycle Sequencing Kit was performed, and the products were loaded on sequencing plates. The fragments were cleaned using sodium acetate (NaAc) precipitation and sequenced on an Applied Biosystems 3730 DNA Analyzer following the manufacturer's protocol.
The raw sequences of Mesanthemum were preliminarily viewed and checked in Geneious R8 (http:// www.geneious.com) (Kearse et al. 2012), as well as the DNA sequences shared by Y. Ito et al. (unpublished data). Forward and reverse sequences with clear pherograms were selected and combined to produce consensus sequences. MAFFT v.7 (Katoh et al. 2009;Katoh & Standley 2013) was used to align the sequences. The alignments produced by MAFFT were then manually checked and improved in PhyDE v.0.9971 (Müller et al. 2010) by examining the gaps and excluding the dubious regions.
Trees were produced with CIPRES (http:// www.phylo.org, Miller et al. 2010) for the five regions separately and for a concatenated (plastid + nuclear) alignment. Syngonanthus species were used as outgroup. The concatenated alignment is available as a supplementary data file (ESM 1).
Before running the analyses, PartitionFinder v.2.1.1 (Lanfear et al. 2012) was used to determine the best fitting partition scheme and the best fitting model for each partition in the concatenated dataset. In this study, the best partition scheme is matK, PHYC, and rbcL+rpoB+rpoC1. For maximum likelihood (ML), GTR+G is the best fitting model for each partition.
For Bayesian inference (BI), GTR+G is the best fitting model for matK and rbcL+rpoB+rpoC1, while HKY+G was determined as the best fitting model for PHYC.
Maximum likelihood analyses of the partitioned data were performed using RAxML v. 8. 2.1 (Stamatakis 2014). Bayesian inference analyses were performed in MrBayes v. 3.2.6 (Ronquist et al. 2012), with the same parameters of partitions as in the ML analyses. MrBayes was run for 100,000,000 generations for 4 runs with 4 chains, keeping a sampling frequency of every 10,000 generations. The first 25% of trees of all runs were discarded as burn-in before generating a majority-rule consensus tree. The final ML and BI trees were viewed and annotated in FigTree v. 1.4.3 (http://tree.bio.ed.ac.uk/software/figtree/).

Morphological study
The morphological work was based on specimens in the Kew herbarium (K), with additional material on loan from Brussels (BR, BRLU), Paris (P) and Zurich (ZT) (Thiers continuously updated). The seeds of seven   Larridon et al. (2019) species available at K, including the two small ephemerals, were examined under a scanning electron microscope (SEM). Three seeds were taken from a representative specimen of each species and mounted dry on stubs with carbon tabs. The stubs were coated for 3 minutes and investigated with a SEM (HITACHI S-4700) with a camera system connected to a computer. The contrast, brightness and background of the images were optimised in Adobe Photoshop CC 2018.

Conservation status
For the conservation assessments, the IUCN (2012) and IUCN Standards and Petitions Subcommittee (2017) were followed. Area of Occupancy (AOO) and Extent of Occurrence (EOO) were calculated with GeoCAT (Bachman et al. 2011).

Molecular study
Here, trees resulting from the concatenated analyses are presented. Maximum likelihood analysis (Fig. 4), with bootstrap (BS) values) and Bayesian inference analysis (Fig. 5), with posterior probability (PP) values) show similar topologies with some small differences. Ericaulon and Mesanthemum represent monophyletic groups in both the ML and BI trees, and Syngonanthus appears as a sister to the clade comprising these two genera (Figs 4,5). The monophyly of Mesanthemum is well supported (BS = 100, PP = 1) and both M. albidum and M. auratum form part of the Mesanthemum clade (Figs 4, 5), although M. auratum is sister to the rest of Mesanthemum in the BI tree (Fig. 5). In the results of the ML analysis (Fig. 4), M. auratum is sister to M. bennae (BS = 73), and the M. auratum + M. bennae clade is sister to the other species of the genus (BS = 100). A sister relationship between M. albidum and M. radicans Körn. is strongly supported in both analyses (BS = 100, PP =1). Mesanthemum prescottianum and M. tuberosum also appear as sister to each other in both trees (BS = 100, PP = 1).

Morphological study
Detailed characters for species are presented in the descriptions (see Taxonomic Treatment). The main morphological differences that distinguish large peren-nial Mesanthemum species from the two ephemeral Mesanthemum species, M. albidum and M. auratum, are their size, reduced floral structures and different seed coat patterning. The height of the ephemeral Mesanthemum species is generally <25 cm, while the perennial species usually grow far beyond this size, even up to 1 m (e.g. in M. radicans). Floral bracts and sepals are absent from the female flowers in M. albidum. Mesanthemum auratum has floral bracts but lacks sepals in both male and female flowers. The perennial aquatic species M. reductum with submerged heads also lacks floral bracts and sepals in both male and female flowers.
In the seed of perennial Mesanthemum species, the cells are irregularly shaped, usually 5 -6-sided, with straight, rather prominent anticlinal cell walls. The angles bear long, thickened, pillar-like projections with expanded truncate tips, as seen in M. radicans (Figs 6A, B). The projections appear as a fringe of colourless hairs under a light microscope, when soaking the seeds in water will usually release the projections. They are held flat in the young seed by the outer cell layer of the outer integument. This disintegrates as the seed matures, as shown in the young and mature seeds of M. alenicola which is formally described below (Fig. 7). Remnants of the disintegrating outer cell layer are also visible in the images of M. bennae (Fig. 6C, D), M. prescottianum (Fig.  6E, F) and M. tuberosum (Fig. 6G, H). The background seed surface is smooth or almost so.
In Mesanthemum albidum the cells are irregularly shaped, 5 -6-walled, and often ± isodiametric as in the perennial species (Fig. 8A, C). However, they lack pillarlike projections from the angles. Instead the anticlinal walls are strongly thickened and prominent, appearing as a white network under a light microscope. These walls in the seed from Adames 363 are heavily coated in a white deposit of crumbly appearance (Fig. 8D). This is a variable feature, as seed from Cheek 18615 has almost smooth walls, with only traces of deposit visible on some walls at high magnification (Fig. 8B). The background relief of the seed surface is verrucose.
The seeds of Mesanthemum auratum differ from those in the rest of the genus, including M. albidum, as the cells are not isodiametric but are elongated in rows along the long axis of the seed (Fig. 9). There is no difference between seeds from plants with white capitula (Fig. 9A, B) or yellow capitula (Fig. 9C, D) from Guinea. The anticlinal walls are prominent but there are no pillar-like projections. Instead, each cell has a linear, slightly sinuous, raised ridge running down the centre, parallel to the long axis but separate from the cell walls. This pattern has not been observed elsewhere in African Eriocaulaceae. Occasionally, these ridges may fork or branch, or are discontinuous (Fig. 9F). The background relief of the seed surface is ruminate, including over the ridges. Seeds from a Cameroon collection (Fig. 9E, F) are larger than seeds from Guinea ( Fig. 9A -D), but show no other significant differences.

Molecular study
Taxonomy of Eriocaulaceae has long been determined by morphological characters, especially by floral struc-tures. In his taxonomic revision, Ruhland (1903) Stützel (1985) also proposed that Eriocauloideae is only comprised of Eriocaulon, and the other two subfamilies derived from it independently. However, this hypothesis was doubted by later researchers. Unwin (2004) conducted a phylogenetic study using molecular data and proposed some evolutionary trends in the Eriocaulaceae. However, Mesanthemum was not included in that study. The phylogenetic position of Mesanthemum in the family was first confirmed by Andrade et al. (2010). Using plastid data of M. radicans, their results placed Mesanthemum as sister to Eriocaulon, and the two genera form a clade that appears as sister to the rest of the family. Their results rejected the third subfamily and strongly supported the monophyly of Eriocauloideae sensu Ruhland (Andrade et al. 2010), providing molecular support for the classification proposed by Ruhland (1903) based on floral morphology.
In the present study, besides Mesanthemum species, molecular data from six Eriocaulon species were included and Syngonanthus angolensis H.E.Hess was selected as outgroup. Our results show that the clade including both Mesanthemum and Eriocaulon is strongly supported (Figs 4,5), which is consistent with Andrade et al. (2010).
As only one Mesanthemum species (M. radicans) was included in the previous molecular study (Andrade et al. 2010), the intrageneric relationships in Mesanthemum are revealed here for the first time.
Despite the different position of M. auratum in the results of the ML and BI analyses (Figs 4, 5), both M. albidum and M. auratum are part of the Mesanthemum clade. Differing from our starting hypothesis based on vegetative and floral characters, these two ephemeral species do not appear to be closely related to each other, which accords with the significant differences in their seed coat patterns. On present evidence the two ephemeral species do not represent a different taxon but are congeneric with the perennial Mesanthemum species.
Mesanthemum albidum appears to be sister to M. radicans (Figs 4,5), despite the considerable differences between them in morphology and life cycle. The phylogenetic position of M. auratum is less clear, appearing either as sister to M. bennae (Fig. 4) or sister to the rest of the genus (Fig. 5). This uncertainty  in placement is likely the consequence of a lack of data. While sequence data for all the five regions was available for M. albidum, only two regions (matK and rpoC1) could be sequenced for M. auratum.
The similarity in size, life cycle and reduced floral parts in the two ephemeral Mesanthemum species is probably the result of convergent evolution. The very distinct seed coat sculpture of M. auratum (Fig. 9) and its potential early branching position in the tree (Fig.  5) leaves a degree of uncertainty about its phylogenetic position. Better plant material of this seldom collected species is needed for further molecular work.
Two accessions of Mesanthemum prescottianum and one of M. tuberosum are strongly supported as forming a clade (Figs 4,5). The two species share many morphological characters, especially the daisy-like capitula, so M. tuberosum was reduced to a synonym of M. prescottianum by Jacques-Félix (1947: 144). In a recent paper (Phillips et al. 2018), M. tuberosum has been resurrected from synonymy, based primarily on field observations including different habitat preferences. Our results show M. prescottianum to be paraphyletic, but based on the limited sampling of this study we do not suggest taxonomic changes at this time.
This study provides a first view of the phylogenetic relationships in Mesanthemum, although further study is needed since some of the perennial Mesanthemum species could not be included at this time, either because the herbarium material available was insufficient or the DNA was too fragmented to enable Sanger sequencing. Further study is also needed to place M. auratum with more certainty.

Morphological study
Six reduced stamens, differentiated into filament and anther, were found around the base of the ovary in dissected female flowers of Mesanthemum pubescens (Lam.) Körn. (Fig. 10) and may be a regular feature in this species. Sterile anthers were also found in some abnormal female flowers of M. cupricola Kimp., but have not been seen elsewhere in Mesanthemum, nor in any of the many species of Eriocaulon in Africa. According to Stützel (pers. comm.) ontogenetical studies in Eriocaulaceae have shown that anthers are always initiated in the female flowers, but do not develop beyond small tissue bumps visible only in extremely young flowers under SEM.
Eriocaulaceae are known to be entomophilous (Stützel 1998: 202). Insects (Coleoptera and Thysanoptera) were noted visiting the flowers of Mesanthemum radicans in Gabon (Wieringa 1139), presumably attracted by nectar from the epipetalous glands. In Mesanthemum, these glands are linear and attached only at the base. They are dark brown, often with a yellow band at the summit, especially well marked in M. bennae and M. pubescens (Fig. 11). The function of the yellow portion and details of the secretions are unknown.
Seeds of Eriocaulaceae species bear various characteristic ornamentations (sculpture) on the seed coat surface, and they have furnished information for the taxonomy of several genera (e.g. Giulietti et al. 1988;Ansari & Balakrishnan 1994;Phillips 1994;Zhang 1999;Barreto et al. 2013). Giulietti et al. (1988) were the first to use SEM to observe the seed coat surface in Eriocaulaceae, and they described different patterns  for 10 genera in the family (Blastocaulon Ruhland is now considered as a synonym of Paepalanthus Mart., and Philodice as a synonym of Syngonanthus). Barreto et al. (2013) studied the seed coat sculptures in Comanthera L.B.Sm. and discovered that the seeds for its two subgenera have very distinct surface ornamentation. The results of these studies suggest that the seed coat sculpture in Mesanthemum may provide information that supports taxonomic hypotheses at a generic or infrageneric level.
Seed morphology in Mesanthemum has been little studied to date. Only the commonest species, M. radicans, was included in previous publications on seed coat sculpture (Giulietti et al. 1988;Phillips 1994). In this study, the seeds of several perennial species and the two ephemeral species were examined. Our results show that there are big differences in seed morphology between the ephemeral species and the rest of the genus. Interestingly, the two ephemeral species are also very distinct from each other.  In Eriocaulaceae, the testa consists of two integuments, an inner and an outer, each integument being itself composed of two cell layers (Zhang 1999). Frequently any thickened ornamentation arises in the inner layer of the outer integument, and this appears to be the case in typical perennial Mesanthemum species (Figs 6, 7). Seed morphology conforms to the same basic plan in all the robust perennial species of Mesanthemum examined: larger seeds with regular-shaped cells and characteristic projections at the corners of the anticlinal walls (Figs 6, 7). The reticulate, uniform cell arrangement formed by 5 -6-sided cells can also be seen in other Eriocaulaceae genera. Similar patterns with long projections at the cell corners were reported in a few Eriocaulon species from Sri Lanka (Phillips 1994) and Paepalanthus gardnerianus Walp. (Giulietti et al. 1988).
The seeds of the two West African ephemeral species, Mesanthemum albidum and M. auratum, are completely different from seeds of the perennial species. No evidence was found in the SEM images of an evanescent outer cell layer (Figs 8,9), but it may disappear very early, as is the case in some ephemeral Eriocaulon species. Furthermore, the differences in seed coat sculpture in M. albidum compared with M. auratum suggest that the two ephemeral species are not closely related to each other, which is consistent with our molecular results.

Conclusion
This study provides the first insight into the relationships between Mesanthemum species based on molecular phylogenetic data. The molecular results and the SEM study of seed coat patterns indicate that the two ephemeral species from West Africa, M. albidum and M. auratum, are not closely related to each other, and their similar habit is likely the result of convergent evolution in similar habitats. Mesanthemum albidum is nested within the generally perennial genus Mesanthemum. The case for retaining M. auratum within Mesanthemum is weaker, but we maintain it as part of Mesanthemum until further study. All Mesanthemum species are here revised. Mesanthemum alenicola is described as a new species from Equatorial Guinea, and only one species is recognised in Madagascar giving a total of 16 species. An identifica-tion key is provided, together with taxonomic notes. Images of the seeds as seen under the SEM are provided where available.
Perennial herbs from a stout tough rhizome or rootstock, rarely aquatic with a slender rhizome; rarely slender ephemerals. Leaves in a basal tuft, linear to linear-lanceolate or ensiform, usually thick, spongy, frequently sparsely to densely hairy, old leaves glabrescent. Scapes many-ribbed, arising from the leaf axils; sheaths cylindrical, obliquely slit with lanceolate limb, scapes and sheaths often sparsely to densely pilose. Capitulum globose or flattened, 4 -35 mm wide. Involucral bracts coriaceous or crustaceous with scarious margins (scarious in M. albidum), in several imbricate series, innermost sometimes radiating beyond the periphery of the floral disc. Floral bracts filiform with expanded, usually hairy tips, rarely absent. Flowers unisexual, trimerous, pedicellate, embedded in a woolly cushion of long receptacular hairs. Sepals free or sometimes basally connate in the male flower, usually membranous, oblanceolate-oblong, concave, often caducous, rarely absent; male flower with a short fleshy stipe between sepals and petals. Petals connate into a fleshy infundibular or oblong tube with shallowly 3-lobed upper margin, petal bases free in female flower resulting in slits in petal-tube around ovary, small slits sometimes also present in male flower, 3 linear brown glands inserted about 2 =3 up inside, petal-tube glabrous or female petal-tube often villous outside and/or within. Stamens 6 arising from base of male petal-tube; anthers usually pale creamy-yellow, rarely dark brown; vestigial gynoecium present. Ovary protruding between petal-tube slits of female flower at maturity; stigmas 3 without appendages. Seeds subglobose, brown, densely covered in white hairlike projections in perennial species.
16 species in tropical Africa, 1 species endemic in Madagascar.
Rosulate perennial from a woody rootstock. Leaves yellowish-green, linear to narrowly subulate, 10 -35 cm long, 5 -12 mm wide, softly pilose, sometimes thinly, older leaves glabrescent, margins firm, tapering to a subacute tip. Scapes 1 -5, 30 -60 cm high, 1.2 -1.5 mm thick, glabrous. Sheaths pilose, limb straight, glabrous or a few hairs within. Capitulum 10 -14 mm wide, densely white-hairy becoming black speckled, hemispherical at first with a shallow involucre slightly smaller than capitulum width, later depressed-globose, involucre reflexing and obscured at maturity. Involucral bracts in 3 -4 series, light brown, all similar, cartilaginous with scarious margins, ovate, 3.0 -4.5 mm long, hirsute, veins visible, glossy brown on inner face, acute or obtuse, inner bracts with an apical patch of white hairs inside. Floral bracts filiform, tip clavate, white-pilose. Receptacle hairs black, curling and tangled. Flowers 2 -3 mm long; sepals black. Male flowers: sepals free, oblanceolate, tips whitepilose, truncate; petals densely white-pilose at tips. Female flowers: sepals as long as petals, oblanceolate-oblong to obovate, tips erose-truncate and white-pilose, otherwise glabrous; petals free below middle, villous with long black hairs on both faces, hairs arising near petal bases, tips densely white-pilose. Seed ellipsoid, c. 1 mm long, dark brown. Fig. 1. Although this species has a restricted distribution range, it is not under any specific threat. It is locally common and reported to be spreading, especially on disturbed ground such as footpaths (J. Timberlake pers. comm.). As a consequence, it has been assessed at Least Concern (LC) by Darbyshire et al. (2017). NOTES. Mesanthemum africanum can be recognised by its hirsute involucre, which becomes hidden as the floral disc matures and expands, together with the copious black receptaclar hairs, black sepals and dense black hairs on both sides of the petal-tube in the female flowers.
The petal-tube hairs arise on the basal claws and lower tube of the petals, not spread over the central portion, as in the similar but more widespread Mesanthemum pilosum. Mesanthemum rutenbergianum from Madagascar also has black receptacular hairs, black sepals and densely black-hairy female petals, but this has a different obconical, non-hirsute involucre still obvious at maturity, and only slightly connate female petals which lack hairs on the outer face. Lecomte (1908Lecomte ( , publ. 1909; Jacques-Félix (1947: 144); Meikle (1968: 65 There are three specimens of Pobéguin 1359 in the Paris herbarium. The specimen designated here as lectotype bears an original handwritten label and also includes a floral dissection. Two specimens exist of the type of Eriocaulon hirsutulum Moldenke (Adam 18370), both from Senegal and collected on 8 October 1961, but with different localities: Asamame (LL) and Kabrousee (IFAN). The specimen in LL is from Moldenke's personal herbarium and the locality matches the protologue, so this specimen is the holotype. In the protologues of Eriocaulon guineense and E. hirsutulum Moldenke describes the female flowers as having 3 oblong sepals, but no sepals were seen in any flowers of M. albidum examined. There are also further differences in the protologue of E. hirsutulum, which has only been seen as an electronic image, but the specimen Adam 18370 in IFAN was seen by Meikle and cited by him as Mesanthemum albidum Meikle (1968). NOTES. This species has showy, bright white, conspicuously fluffy hairy capitula, and can be further recognised by its conspicuously white-reticulate seeds. Van der Burgt 2018 has a peripheral circle of fully developed, long pedicellate, exserted male flowers in the capitula. In all other specimens seen there are only slender rudiments resembling the pedicels of male flowers. Tufted perennial from a rootstock or short rhizome. Leaves in a loose rosette, ascending or arching outwards when short, linear or linear-subulate, flat or folded, 8 -30 cm long, 5 -12 mm wide, papery, pilose to hispid on both surfaces, tapering to a hard acuminate tip. Scapes up to 10, relatively slender, 30 -56 cm high, 0.5 -1.1 mm thick, erect at first, later drooping, hirsute with spreading colourless hairs 1 mm or longer. Sheaths shorter or as long as the leaves, narrowly cylindrical, hirsute, limb 2 -3 cm long, acuminate. Capitulum viviparous, tuft of small leaves arising from centre of cup-shaped involucre, 5 -8 mm wide, a circlet of white-villous flowers visible around periphery. Involucral bracts in 3 -4 series, pale straw tinged green with paler thinner margin, crustaceous, indistinctly veined, silky-pilose on back with appressed hairs, upper margins ciliate, outermost bracts ovate, 2.3 -2.5 mm long, inner progressively longer and usually more oblong, innermost 3.5 -3.6 mm long, subacute or obtuse. Floral bracts few, filamentous, tip not expanded, thinly penicillate with short white hairs above middle or towards tip. Receptacle hairs fuscous or dark grey. Flowers 3 -4 mm, female subsessile, male pedicellate; sepals colourless. Male flowers: sepals free, oblong-spathulate narrowed to a slender base, laterals keeled, median flat, membranous, back densely white-villous above middle, inner face white-villous towards tip; petal-tube fleshy with 3 small slits near base, upper margin 3-lobed, lobes rounded, densely white-villous on margin and back; anthers 6, creamy-white. Female flowers: sepals free, 1 = 3 -½ length of petal-tube, 1.0 -1.3 mm, ovate, concave, membranous, acute or denticulate; petals linearoblong, lightly adherent and easily splitting in central area, connate portion glabrous outside and within, free lobes densely white-villous on outer face and tips, lateral petals with dark gland, median petal eglandular. Seed almost spherical, c. 0.8 mm, dark reddish-brown, covered in clinging white prickle-hairs. Figs 7, 13.

Mesanthemum albidum
RECOGNITION. Mesanthemum alenicola differs from the widespread species M. radicans by its more slender drooping scapes, smaller viviparous capitula with a cupshaped (not turbinate) involucre of more obviously hairy involucral bracts, and by the female flowers with very short sepals and a glabrous (not villous) petal-tube. DISTRIBUTION HABITAT. Rock pavement in grassland and low bushland, on black soil rich in humus; 1110 -1130 m. CONSERVATION STATUS. Mesanthemum alenicola is only known from three collections at one location in Monte Alén National Park in Equatorial Guinea. More information is needed to confirm that it is endemic to this location only, to assess the population size and to assess threats to this species, currently unknown. It is here assessed as Near Threatened (NT) in the absence of any credible threat being known. Should a threat be discovered the species should be reassessed as Critically Endangered (CR) under Criterion B2ab. ETYMOLOGY. The specific epithet refers to the mountain range where this species occurs. NOTES. This species exhibits the only known case of vivipary in Mesanthemum, although vivipary occurs in several species of Eriocaulon. It may be facultative, as a single very mature capitulum without a central viviparous leaf tuft contained a number of ripe seeds. The capitula are smaller than is usual in the genus, although the habit is otherwise typical. The sepals of the female flowers are very short, barely extending above the level of the ovary. Mesanthemum radicans is similar, but besides the differences given above usually has slightly wider leaves, and grows in swampy grassland and bog generally at lower elevations, not on rock pavement.
Mesanthemum angustitepalum Kimp. (Kimpouni 1994: 149 Robust rosulate perennial from a tough rootstock. Leaves linear or narrowly linear-lanceolate, up to 55 cm long, 7 -10 mm wide, herbaceous, hirsute on both surfaces, tip, subacute, hard. Scapes 1 -3, 28 -55 cm high, stout, 1.6 -1.8 mm thick, hirsute with patent hairs. Sheaths hirsute, limb acute. Capitulum 13 -16 mm wide, hemispherical, white-hairy from an involucre with flat base as wide as floral disc. Involucral bracts in 3 -4 series, pale greenish-brown, crustaceous, outer bracts broadly ovate, 3.0 -4.5 mm long, pilose on exposed part, hairs dense towards tip, veins and margins inconspicuous, tip acute, innermost bracts narrowly oblong, white-pilose above middle and on exposed inner face. Floral bracts filiform, subulate and densely white-pilose above middle. Receptacle hairs black, some hairs also on pedicels of female flowers. Flowers 3.0 -3.5 mm long; sepals colourless. Male flowers: sepals free, narrowly oblong, scattered hairs on back, tips densely white-pilose, obtuse; petal-tube with slits at base, upper margin shallowly 3-lobed, lobes broadly rounded, white-ciliate; glands at midpoint of petals inside. Female flowers: sepals c. 2 = 3 petals, membranous, narrowly elliptic-oblong, tips densely whitepilose, acute; petals free around ovary, connate above, villous outside and within with dense black hairs extending to middle or above from base and margins of free lower portion, hairs outside grading into white hairs along upper seams of petal-tube, hairs inside extending to level of glands c. 2 = 3 up tube, tips shallowly rounded, densely white-ciliate. Seed subglobose, 0.6 -0.8 mm long. Fig. 2A. Mesanthemum angustitepalum is a perennial herb restricted to pools on iron pan, and is known only from two locations in the Upemba National Park in Katanga, southeastern Democratic Republic of Congo. Upemba National Park is confronted with many threats ranging from poaching, illegal settlements and the presence of illegal permits to mining and hydroelectric interests (https:// saveupemba.com/). However, the effects of these threats on M. angustitepalum, and the occurrence, number of locations and distribution of this species, remain unknownwith the last known collection of this species made in 1949 despite numerous surveys for rare plant species in Katanga connected with the mining industry in recent years. It is here assessed as Endangered (EN) B1ab(iii)+2ab(iii). NOTES. Young specimens of Mesanthemum pilosum Kimp. are similar to M. angustitepalum, but the leaves and involucral bracts are usually less hairy, and the receptacle hairs are grey rather than black. At maturity the capitula of M. pilosum become globose with inturned involucral bracts, whilst those of M. angustitepalum remain hemispherical. Both species have villous female flowers, but the hairs arise differently. The sepals of M. angustitepalum are glabrous except for white hairs at the acute tips, whereas the sepals of M. pilosum are long-villous from the base and margins as well as having white hairs at the denticulate tips. The female petal-tube is villous inside in M. angustitepalum, but glabrous inside in M. pilosum.
Mesanthemum angustitepalum is contrasted in the protologue with M. jaegeri Jacq.-Fél., a West African species found among rocks and on inselbergs. It has large rosettes from a whitish, swollen base, with larger capitula (15 -20 mm wide), female flowers with the sepals as long as the flower (not shorter), and the petal-tube is glabrous inside (not villous). Lecomte (1908Lecomte ( , publ. 1909  its number of locations nearly meets the threshold for Vulnerable (13 > 10); and continuing decline of area, extent and quality of habitat has been observed and/ or inferred at various locations. Therefore, Mesanthemum auratum is here assessed as Near Threatened NT B2ab(iii). However, the taxonomic status of this species is not entirely resolved (see notes below). NOTES. There appear to be two colour variants of this species. The extraordinary yellow-orange colour of the hairs on the floral bracts and flowers of some collections (including the type) is unique in Eriocaulaceae. Yellow-flowered specimens have only been collected from a restricted area around the town of Kindia in Guinea. Despite the striking colour of the flowering plants, this variant has not been collected since 1956 and recent searches of the area have failed to find it. There appear to be no significant morphological differences between this and the more widespread white-flowered form, which also grows in the same habitat around Kindia. Both colour forms have the same seed ornamentation (Fig. 9A -F).

Mesanthemum auratum
According to the protologue (Lecomte 1909) Mesanthemum auratum flowers in profusion towards the end of the wet season, forming carpets, then completely disappears in the dry season. Material collected in early October is rather young, the male flowers unfurling their stamens, but the female flowers still immature. A plant with ripe seed was collected in late October. By early February all seed has been shed and no male flowers were present.
Mesanthemum albidum, several Utricularia species and Genlisea species occur in similar habitat. Collections of M. albidum are often mixtures with M. auratum. When white, the fluffy heads and delicate habit are very similar to those of M. albidum, but M. auratum can be distinguished by its obvious brownblack involucre of much tougher bracts at the base of the capitulum. Mesanthemum auratum lacks sepals in both the male and female flowers, whereas M. albidum lacks them only in the female flowers.
The conspicuous plumose floral bracts of Mesanthemum auratum are lacking in M. albidum, where the fluffy white hairs are borne on the flowers. However, the plumose bract-tips are fragile, easily breaking off and are absent in seeding capitula. Sometimes even most plumose floral bracts are absent, or only one or two are present. The fluffy appearance of well-developed capitula is then lacking, the dark brown involucre being the most obvious feature of the capitulum. This is the case with the specimens from Guinea-Bissau and Sierra Leone cited here and by Meikle (1968: 65), which have very sparse whiteplumose floral bracts.
On well-developed specimens (e.g. Cheek 18636) the petals, although tiny in both flowers, are villous and provided with a penicillate gland on the inner face. However, frequently the petal lobes are scarcely developed and then are glabrous with the gland on the tip. The filaments found within the cushion of receptacular hairs were tentatively suggested to be sepals by Lecomte (caption to Fig. 1, p. 600, 1909). However, they are inserted on the receptacle separately from the flowers, and as they sometimes have a minute yellow spot at the tip, are more likely to be reduced floral bracts (although not obviously subtending flowers) or perhaps sterile pedicels. Insects (Coleoptera and Thysanoptera) were noted visiting the flowers of Wieringa 1139 (Gabon).
This species remains enigmatic, and possibly more than one species is included here. The variably reduced flowers, colour differences and often overmature collections make comparisons difficult. The herbarium material available was not ideal for molecular study. The two specimens cited above from Sierra Leone were collected between 1600 -1900 m, considerably higher than collections from Guinea. However, no substantive differences were found in the specimens examined, and the dark brown involucral bracts are distinctive.
Robust tussocky perennial from a stout rootstock. Leaves ascending, ensiform or linear-elliptic and tapering to base, 20 -48 cm long, 15 -65 mm wide, fleshy becoming tough when dry, hirsute on both surfaces when young, old leaves glabrescent, margins firm, tapering to a hard acuminatecuspidate tip. Scapes 2 -6, erect, stout, 30 -74 cm high, 1 -2 mm thick, densely pilose with patent hairs, many-ribbed. Sheaths shorter than leaves, hirsute with patent hairs, limb hirsute within, tip hard, acuminate-cuspidate. Capitulum 20 -45 mm wide, daisy-like, white becoming buff when old, involucre much exceedng floral disc. Involucral bracts in 5 or more irregular series of increasing length, indistinctly many-veined, outer bracts forming a shallow cup at capitulum base, 4.5 -7 mm long, ovate, hirsute, cream-coloured or pale green, acuminate, inner series radiating raylike much beyond floral disc, 9 -20 mm long, lanceolate-oblong, papery, white-velutinous on both surfaces, acute. Floral bracts filiform, tips expanded, bearded with white hairs. Receptacle hairs grey or colourless. Flowers 3.5 -3.8 mm long, pedicellate; sepals colourless. Male flowers: sepals free except at extreme base, narrowly oblong or oblanceolate, membranous, concave, tips pilose, obtuse; petal tube glabrous within, upper margin shallowly 3lobed, white-pilose, glands dark brown with yellow tips; anthers cream-coloured. Female flowers: sepals free, narrowly oblong, membranous, concave, laterals slightly keeled, tips white-pilose; petals free in lower third, connate above ovary, petal-tube densely whitepilose outside towards tip, glabrous below or with a few longer colourless hairs or sometimes these denser, glabrous within. Figs  HABITAT. Cracks in vertical sandstone cliffs with seasonal water seepage; 360 -1300 m. CONSERVATION STATUS. Mesanthemum bennae is the most spectacular species of the genus in flower with several brilliant white heads up to 4.5 cm in diam. It is restricted to sandstone cliffs on the Benna-Kounounkan Plateaus near Kindia in Guinea, and has been observed to be threatened by fires set artificially (X. van der Burgt pers. comm.). It is likely that the entire global population amounts to some thousands of plants, and is assessed as Endangered EN B1ab(iii)+2ab(iii). TYPIFICATION. There are three specimens of Jacques-Félix 2091 in the Paris herbarium. The specimen with a handwritten label is designated here as lectotype. NOTES. Mesanthemum bennae is a showy species, with its large white daisy-like heads from a broad-leaved basal rosette. It appears to have a very restricted distribution in Guinea, on vertical sandstone cliffs that are difficult to access. The only other species with similar showy daisylike flowers is M. prescottianum, which also occurs in Guinea. This can be distinguished immediately by its much narrower, grassy leaves and almost glabrous long ray-like involucral bracts. Additionally, M. prescottianum is found on granite outcrops, not sandstone cliffs. Van der Burgt notes that M. bennae is not at all resistant to fire, never occurring in grassland that is burned annually.
RECOGNITION. Mesanthemum cupricola is close to M.variabile, both beingrelatively slender specieswith narrowly linear leaves; flat-topped capitula; coarse blackish receptacle hairs; short broad sepals in the female flowers; and hairy margins to the claws of the petal-tube. However, they can be easily distinguished by the involucral bracts which are sharply pointed, extending shortly beyond the floral disc, and with longershaggierhairsinM.cupricola.Mesanthemumvariabilehas more rounded involucral bracts with an obvious margin and a fine silky appressed pubescence.
Mesathemum cupricola is compared in the protologue to the common species M. radicans (Benth.) Körn. Mesanthemum radicans is a more robust, usually less hairy species with longer (up to 50 cm), wider (8 -15 mm), scattered-pilose or glabrescent leaves. The involucral bracts are rounded to obtuse (not sharply pointed) with conspicuous veins towards the tips, and a shorter silky pubescence. The innermost bracts extend clearly 2 -3 mm beyond the floral disc. The receptacle hairs in M. radicans are a paler grey colour, not blackish and wiry. M. radicans is a species of lowland marshes, not known above 1200 m. DISTRIBUTION HABITAT. Ponds on ironpan pavement and copper rich soils; c. 1400 -1500 m. CONSERVATION STATUS. It is endemic to Katanga in southeastern Democratic Republic of Congo. It is only known from two collections made on heavy-metal polluted sites. The copperbelt area in the Democratic Republic of Congo is heavily impacted by open cast mining. This species has not been observed since 1959 at its only known location. Field surveys are needed to confirm whether the species is extant. Therefore, it is assessed as Critically Endangered CR B2ab(ii,iv) and possibly Extinct. NOTES. Mesanthemum cupricola appears to be endemic to the copper rich soils of the copperbelt in southern D.R. Congo.
Some flowers from the type specimen show abnormalities. Apparently female flowers with a narrow cylindrical petal-tube and free basal claws were found to contain stamens when opened as well as an ovary, although the anthers may not be well developed. The number of anthers is variable: 3, 4 and 6 anthers were observed in three separate flowers. The sepals are longer, resembling those of the male flowers, but the ovary is larger than the vestigial ovary of typical male flowers. Typical male flowers always have an infundibular petal-tube containing six anthers, a vestigial ovary at the base, and sepals as long as the flower, as is usual in the genus. Additionally, the female petal-tube is normally glabrous within, but one flower was found which was densely villous inside. This character is usually stable within species and useful for identification. One flower was found with branching petal glands. These floral abnormalities and perhaps the bicoloured leaves may be due to the polluted habitat. Tufted perennial, occasionally developing a short rhizome. Leaves in a loose rosette, linear or subulate, up to 20 (-40) cm long, 3 -6 (-8) mm wide, spongy, glabrous on lower surface, hirsute above, sometimes sparsely or glabrescent, margins incurling (at least when dry), tip thickened, obtuse. Scapes 1 -3, slender, 40 -75 cm high, 0.7 -1.1 mm thick, glabrous to hirsute. Sheaths hirsute, often longer than the leaves, limb narrowed to a shortly rostrate obtuse tip. Capitulum 9 -15 mm wide, bright white, flat topped with a turbinate involucre, floral disc densely whitepilose, involucral bracts not exceeding floral disc.
Involucral bracts in 4 -5 series, brownish-green with a broad pale scarious margin, strongly ribbed in upper half, smooth below, essentially glabrous (some short marginal cilia), outermost 3.7 -5.0 mm long, ovateoblong, inner progressively longer and more oblong, innermost 4.5 -5.5 mm long, tips obtuse to broadly rounded. Floral bracts filiform, a dense brush of white hairs on expanded rounded tip. Receptacle hairs pale to dark grey-brown. Flowers 3 -4 mm long; sepals colourless. Male flowers: sepals connate at extreme base, narrowly oblong, tips white-pilose, hairs eventually caducous. Female flowers: sepals resembling male sepals, as long as petals, glabrous on back, white-pilose at the truncate, denticulate tips; petals narrowly oblong, variably free up to about halfway, connate above, villous with long grey-brown hairs both outside and within up to level of glands (but margins glabrous), free tips densely white-pilose. Seed broadly ellipsoid, c. 0.9 mm long, dark brown. Fig. 2C. Mwinilunga, 22 Jan. 1975, Brummitt, Chisumpa & Polhill 13998 (K!). HABITAT. Wet peaty soil of dambos and pools or marshy ground near rivers; 1100 -1500 m. CONSERVATION STATUS. Mesanthemum glabrum occurs in at least 13 locations and has a very broad distribution with an EOO of 496,512 km 2 . Its known area of occupancy is small (60 km 2 ) although it may have been undercollected. There are a number of continuing threats to its habitat associated with agriculture and housing development. However, recent collections (2015 -2016) have been made in four locations where it was found to be frequent. One of these locations had recently undergone extensive agricultural development, meaning that this species is still locally common despite the change of land use. Since it is close to the threshold of ten locations for Vulnerable under Criterion B2, it has been assessed as Near Threatened (NT). There are planned hydroelectric developments (2015 -2025) in Angola within this species' distribution range, which might have future impacts on habitat and increase the threat level to this species. It is therefore suggested that seeds should be banked for ex situ conservation and the assessment is repeated in 5 years. NOTES. This relatively slender species occurs on wet peaty soil at middle altitudes in central Africa. The heads have a top-shaped greenish involucre of neat, rather narrow, conspicuously pale-margined and prominently veined glabrous bracts, which support the bright white floral disc. The petal-tube of the female flowers is conspicuously villous with grey-brown hairs both outside and within.
Drummond & Cookson 6444 (W Zambia: Kalabo, 13 Nov. 1959) is a vigorous specimen matching Mesanthemum glabrum, but with dark brown coloration in the involucral bracts and a brush of long hairs from the pedicel-tip of the male flowers. Further collections are needed to determine its status.
Robust perennial from a short, very stout rhizome clothed in decaying leaf remnants, base often bulbously swollen. Leaves linear to broadly lanceolate, 15 -30 cm long, 7 -25 mm wide, thick, hirsute at first, glabrescent, expanded bases papery and whitish, margins firm, tip acute. Scapes up to about 10, stout, 25 -45 cm high, 1.6 -2.2 mm thick, hirsute with spreading hairs. Sheaths about half as long as leaves, hirsute with spreading hairs, limb with hard acuminate tip. Capitulum 15 -20 mm wide, flat-topped with a broad, shallow, cup-like involucre slightly shorter than capitulum width, white-hairy flowers and bracts protruding from a conspicuous cushion of black hairs. Involucral bracts in 3 -4 series, pale brown, firmly membranous or finally coriaceous with broad hyaline margins, c. 5 mm long, ovate-oblong to broadly ovate, 5-veined, softly pilose on exposed portion, margins ciliate above middle, outer bracts apiculate, inner bracts acute, innermost not extending beyond floral disc. Floral bracts filiform, tip clavate, white-villous. Receptacle hairs wiry, black. Flowers c. 5 mm long; sepals pallid. Male flowers: sepals connate at extreme base, narrowly oblanceolate-oblong, back thinly pilose with scattered long hyaline hairs, tip obtusely triangular and densely pilose with stout white hairs; free petallobes densely white-pilose around margins. Female flowers: sepals longer than petals, slightly narrower than male sepals but otherwise similar; petals free near base, central connate portion glabrous outside, villous with long grey hairs within, free tips truncate, densely pilose with short stout white hairs. Seed plumply ellipsoid, c. 0.8 mm long, dark brown. HABITAT. Among rocks on mountains and damp rockfaces of inselbergs; (600 -) 1300 -1500 m. CONSERVATION STATUS. Mesanthemum jaegeri is fairly widely distributed. However, based on herbarium label data of collections made in the past 80 years, the habitat is limited to mountainous regions (AOO = 44 km 2 ), which form a small fraction of the EOO (957,614 km 2 ). Applying Criterion B, the AOO is smaller than the thresholds for Vulnerable and Endangered, and the number of locations (8) falls within the threshold for Vulnerable. Furthermore, loss or degradation of habitat due to human activities is inferred. Therefore, the species is assessed as Vulnerable VU B2ab(iii). NOTES. Mesanthemum jaegeri is a West African species found in wet rocky places in uplands. It usually has hairier leaves than M. radicans, which grows in marshy places at lower elevations. The bulbous plant base and conspicuous cushion of black wiry hairs in the capitulum are distinctive.
Robust tussocky perennial from a woody rootstock or shortly elongating rhizome, old burned leaf remains often present at base. Leaves clustered at rhizome branch tips, linear, grass-like, pale green, 15 -30 cm long, 8 -12 mm wide, usually pilose on both surfaces but varying from glabrescent or pubescent to velutinous, tip hard. Scapes solitary, 25 -75 cm high, stout, 1.3 -1.8 mm thick. Sheaths pilose, limb glabrous within. Capitulum 12 -16 mm wide, densely whitehairy, hemispherical becoming subglobose at maturity, involucre flat across capitulum base at first, outer bracts extending almost to capitulum periphery, inner equalling floral disc, reflexing and inconspicuous at maturity. Involucral bracts in 4 -5 series, brownishgreen, coriaceous with narrow hyaline margins not extending round tip, outer bracts 4.5 -6.0 mm long, ovate, glabrous or puberulous, veins visible, margins ciliate, tip subacute, inner more oblong, whitetomentose on inner face towards tip. Floral bracts filiform, tip subulate, white-villous, extending above flowers. Receptacle hairs pale to dark grey. Flowers 2.5 -4.0 mm long; sepals brownish-grey. Male flowers: sepals free, thinly cartilaginous, narrowly oblong, tips whitepilose. Female flowers: surrounded by a dense circlet of long, soft, grey hairs from base of flower and sepalbases; sepals half as long as petals, oblong or obovateoblong, long-villous with straight colourless or pale grey hairs at base, some similar hairs also along margins, tips irregularly dentate, glabrous or few to many long marginal hairs; petals unequally free to middle or above, silky-villous near and along free margins outside, glabrous within, glands at midpoint inside, tips membranous, c. 0.5 mm, white-pilose or subglabrous. Seed elliptic-oblong in outline, c. 0.9 mm long, brown. Fig. 2D 24 Sept. 1968, Mutimushi 2716 HABITAT. Grassland often subjected to burning, in wet boggy areas (dambos); 1000 -1700 m. CONSERVATION STATUS. Mesanthemum pilosum is fairly widely distributed in Angola, the Democratic Republic of Congo (Katanga Province), Malawi, and Zambia (EOO = 887,045 km 2 yet AOO is only 56 km 2 ), where it is found in grassland often subjected to burning, and in wet boggy areas (dambos). Although the area, extent and/or quality of its habitat may be impacted by human activities and/or drought in some locations, its presence has been confirmed in at least two protected areas, and other known occurrences are near protected areas (particularly in Zambia). Targeted fieldwork will likely confirm its presence in the some of the latter. It is here assessed as Near Threatened (NT) since 13 locations are known, close to the threshold of 10 for Vulnerable B2a. TYPIFICATION. The holotype was destroyed during transport from Belgium to Poland in the 1990s. An isotype is selected above as lectotype. NOTES. Mesanthemum pilosum occurs across southcentral Africa in wet patches in open grassland. The tussocky rosettes bear globose, white-hairy heads at maturity. The long circlet of silky hairs surrounding the disarticulated female flower is a good spot character, but female flowers are sometimes few. Damann (Angola s.n., 7 Nov. 1959 (ZT)) notes "first leaves appear on burned swampland in early September; plants in full flower by early October; most flowers finished by early November".
NOTES. Mesanthemum prescottianum has a restricted distribution in the far west of Africa and is known only from thin soil over rock, to which it is very tightly affixed. It varies considerably in vigour, capitulum size, hairiness of the involucral bracts, and the colour of the hairs in the capitulum. However, it is always immediately recognisable by its shiny white daisy-like capitula with long, ray-like, usually pointed involucral bracts. The dark anthers of this species and M. tuberosum appear to be unique in the genus, other species having creamy-white or yellowish anthers. Mesanthemum prescottianum flowers late in the wet season, reaching peak flowering in August and September and seeding in late October and November, the dried capitula persisting on the plant. It typically grows directly on rock in seasonally wet places, never in permanent standing water or marsh. scattered hairs, subacute to obtuse, inner bracts patchily appressed silky-pilose on thinner marginal tissue, margins ciliate, innermost bracts oblong, equalling or exceeding floral disc by up to 1 mm, densely appressed white-tomentose on exposed inner face. Floral bracts filiform, tip oblanceolate, white-tomentose.
Receptacle hairs brownish-black. Flowers: 3.0 -4.0 mm long, female flowers peripheral, subsessile; male flowers central, pedicellate; sepals brownish-black. Male flowers: sepals almost free, oblanceolate-angulate, densely white-pilose towards broadly obtuse tip, hairs spreading slightly inside. Female flowers: sepals 3 = 4 as long to subequalling petals, narrowly oblong, broadly obtuse, glabrous to densely white-pilose around tip; petals oblanceolate, lightly connate from upper 2 = 3 to subapically, easily separating, glabrous on outer face, lanate from lower 1 = 3 inside, the woolly blackish hairs extending almost whole length of petals and protruding out of sides, upper margin membranous, truncatecrenate, white-pilose; 6 vestigial yellow stamens c. 0.5 mm long at base of ovary. Seed not seen.  (Rakotonirina & Faranirina 2017a, 2017b. Although the species experiences continuing decline due to threats including agriculture, mining & quarrying, nomadic grazing, wild fires, soil erosion and sedimentation, the combined distribution range and number of locations will unlikely qualify for any of the IUCN threat categories (IUCN 2012; IUCN Standards and Petitions Subcommittee 2017). NOTES. The differences given by Moldenke (1955: 30) between Mesanthemum pubescens and M. rutenbergianum were not apparent in the specimens studied here. Jacques-Félix (1947: 144) distinguished these two mainly by leaf shape and pubescence, and whilst plants with narrower linear leaves do tend to be hairier, there are also narrow-leaved plants with glabrous leaves. Leaf width and pubescence appears to be variable, as it is in some other species of the genus. Therefore, they are combined here as the single species M. pubescens, which is endemic to Madagascar.
The drawing of Mesanthemum rutenbergianum in Ruhland (1903: 119) shows the female flowers with petals connate above the ovary in the upper two-thirds. This is an error, as the petals are loosely connate only towards the tip as described in his description, often being almost free with the dense curly hairs inside protruding through the slits. This is a very characteristic feature of M. pubescens. Vestigial stamens surrounding the base of the ovary in the female flowers have not been reported previously in Mesanthemum (Fig. 10). Apparently female flowers with a narrow petal-tube were also found to contain quite welldeveloped anthers in M. cupricola Kimp. TYPIFICATION. The specimen in the Lamarck herbarium (P-LAM; microfiche LM-667/4) must be the basis of Lamarck's protologue and is designated here as lectotype. Another specimen in Paris collected by Commerson (labelled "isotype" by Moldenke) consists of a single scape and sheath without any leaves [P00102948]. A further Commerson specimen from Herb. Jussieu [P00675322], comprises a whole plant.
The holotype of Mesanthemum rutenbergianum, collected in Madagascar by Rutenberg at Mahamba, near the Alaotra, on 18 Dec. 1877, appears to be lost. According to Dorr (1997: 418), Rutenberg was murdered in Madagascar, but some of his specimens were later returned to Bremen. Evidently his specimen forming the basis of this species was among them, as it was described by Körnicke who worked in Bonn. Soon after WWII many types in German herbaria were taken by Soviet troops and deposited in LE. These were later returned to Germany, but it has not proved possible to locate this particular type specimen. The specimen Hildebrandt 3714 (K) is a good match with the protologue, so is designated here as neotype.
The two forms of Mesanthemum pubescens, f. alba and f. nigra, described by Jacques-Félix are of no significance. He himself proposed them with some doubt, dependent on further collections. The specimen of Baron 458 (Kew), cited under f. alba, in fact has black (not whitish) sepals, and no specimens of this species have been seen with pale sepals. The names are included in the synonymy above for completeness only.
CONSERVATION STATUS. Mesanthemum tuberosum is a localised species endemic to the high altitude seasonally wet sandstone bowal grassland of the Fouta Djallon highlands of Guinea. It bears flowers in June in the wet season, and is unusual in having a fleshy basal corm buried in its sandy habitat. It is known from 9 locations, although some of these have not been verified for a number of years. Its habitat is impacted at several locations by cattle grazing and trampling and by modification of habitat for cultivation (Cheek pers. obs. June 2016; Phillips et al. 2018). There is also the threat of mining for bauxite. Based on current evidence and the lack of any protection for this species, it is assessed as Vulnerable VU B1ab(iii)+2ab(iii) . NOTES. Mesanthemum tuberosum is closely related to M. prescottianum, confined to the Fouta Djallon area of Guinea. It occupies a different habitat from M. prescottianum, on sandstone flats rather than on rocky outcrops, and also flowers earlier at the start of the wet season (June -July). In dissected specimens the female flowers were few in the axils of the involucral bracts, flowers of the central floral disc being apparently all male. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/ licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.