Introduction

Tragia L. is a genus of about 150 species of often-climbing herbs and shrubs, widely distributed in tropical and warm-temperate regions of the world, with its highest diversity in Africa and America but extending to Asia and Australia (POWO 2024, continuously updated). Africa is the region with the highest concentration of described Tragia species, with more than 80, almost all of which are endemic to the continent. Within Africa, the regions with the most known species are South Tropical Africa (Angola, Malawi, Mozambique, Zambia and Zimbabwe, with 31 species), East Tropical Africa (Kenya, Tanzania and Uganda, with 28 species) and Northeast Tropical Africa (Chad, Djibouti, Eritrea, Ethiopia, Somalia, Sudan and Yemen with 23 species) (POWO 2024, continuously updated). The genus is the largest of the tribe Plukenetieae in the subfamily Acalyphoideae and the sixth largest of Euphorbiaceae after Euphorbia L., Croton L., Acalypha L., Macaranga Thouars and Jatropha L. (POWO 2024, continuously updated). Plukenetieae are distinguished by their frequent twining habit and floral and pollen morphology. Within Plukenetieae, Tragia is the type genus of the subtribe Tragiinae, characterised by often abundant, urticating hairs and the absence of stipels or laminar glands on the leaf blade bases (Webster 1994; Cardinal-McTeague & Gillespie 2016). In a recent literature review, 26 species of Tragia were found to be used as medicinal plants, mainly in East Africa and the Indian subcontinent. One of the species in particular, Tragia involucrata L., is used in Ayurveda, with documented uses appearing as early as the 1st century CE (Duarte-Casar & Romero-Benavides 2021).

The genus needs revision. Floral and pollen morphology suggest that Tragia is not monophyletic, with the other genera of Tragiinae embedded within it (Gillespie 1994). Recently, four sections of Tragia were reinstated as genera: Bia Klotzsch (Webster 2007), Zuckertia Baill. (Medeiros et al. 2013), Ctenomeria Harv. (Webster 2014) and Monadelpha L.J.Gillespie & Card.-McTeag. (Gillespie et al. 2020), based on inferences from pollen morphology (Gillespie 1994) and phylogenetic data (Wurdack et al. 2005; Cardinal-McTeague & Gillespie 2016). A recent molecular phylogeny confirms that Tragia, even after taking into account the removal of these reinstated segregate genera, remains para- and or polyphyletic. Consequently, a major revision is necessary to establish a generic classification that accurately reflects monophyly and evolutionary history (Cardinal-McTeague & Gillespie 2016).

In this paper, we describe Tragia grandistipularis sp. nov., a new species from the Phalombe District in the Southern Region of Malawi, which was collected in 2014 by staff of the Forestry Research Institute of Malawi and the National Herbarium and Botanic Gardens of Malawi. A specimen was sent to Kew as the herbarium voucher for a Millennium Seed Bank collection of seeds held at Wakehurst Place. The first author noticed that the specimen did not match any of the known species, showed it to the third author, and discussed its status on her visit to the Kew Herbarium in April 2023. The new species is remarkable for having unusually large stipules, up to 15 mm long and 10 mm wide, which are much bigger than those of any other known African Tragia species, including T. stipularis Radcl.-Sm., which was previously noted for its large stipules but which are only up to 10 mm long and 7 mm wide.

Tragia was last revised in this region in Flora Zambesiaca (Radcliffe-Smith 1996); T. grandistipularis is the only new species from the area described since then. The genus is represented by 29 species in the Flora Zambesiaca area (Botswana, Malawi, Mozambique, Namibia Caprivi Strip, Zambia, and Zimbabwe), including the new species, with ten species occurring in Malawi (Radcliffe-Smith 1996; Hyde et al. 2024): T. adenanthera Baill., T. benthamii Baker, T. brevipes Pax, T. grandistipularis sp. nov., T. hildebrandtii Müll.Arg., T. kirkiana Müll.Arg., T. lasiophylla Pax & K.Hoffm., T. okanyua Pax, T. rhodesiae Pax, and T. shirensis Prain. All, except T. rhodesiae, are known to occur in the Southern Region of Malawi, only T. kirkiana and T. okanyua have been collected in the Phalombe District (Zacharia Magombo, based on specimens at MAL), but no Tragia species has been mentioned in the district in the available literature (Radcliffe-Smith 1996; GBIF.org 2024; Hyde et al. 2024). The only other genus of subtribe Tragiinae that occurs in Malawi is Tragiella Pax & K.Hoffm., with two species known to occur in the country, T. anomala (Prain) Pax & K.Hoffm. and T. natalensis (Sond.) Pax & K.Hoffm., but it differs from Tragia in the styles united to form a tube or globose mass (vs styles free above).

We provide a description and illustration of the new species, an evaluation of its conservation status, and an amendment to the key to the genus in Flora Zambesiaca.

Materials and Methods

Identification of the new species was undertaken using relevant literature, including Flora Zambesiaca (Radcliffe-Smith 1996) and Flora of Tropical East Africa (Radcliffe-Smith 1987). In particular, stipule measurements of all species included in both Floras were checked. Only a single collection of the new species is known, and it was examined under a Leica MZ6 binocular microscope. All measurements were taken from the dried specimen. Hair density terms are defined as follows: sparse when hairs are scattered enough not to touch when pressed towards each other; abundant when hairs are close enough to touch if pressed towards each other and dense when hairs are so close to each other that they hide the surface of the organ they grow on. Other terms, and the format of the species description, follow Flora Zambesiaca (Radcliffe-Smith 1996), for easier comparison with the other Tropical Southern African species; the species description also includes some more general features that characterise or may be variable in the genus. Specimens of the genus from the Flora Zambesiaca area were studied at Kew (K), at the National Herbarium of Malawi (MAL) and at the Forest Research Institute of Malawi (FRIM), and specimen images were consulted from GBIF (2024). Herbarium acronyms (except FRIM) follow Thiers (2024, continuously updated). All cited specimens have been seen by the authors. The preliminary conservation status is proposed in accordance with the IUCN Red List Category Criteria and guidelines (IUCN 2012, 2022).

Taxonomic Treatment

Tragia grandistipularis Cahen, Magombo & L.J.Gillespie sp. nov. Type: Malawi, Southern Region, Phalombe Distr., Boydi village, UTM 36L 788354 8273676 [15°35'53.92"S 35°41'20.22"E], 633 m, 25 March 2014, Chapama, Mphamba & Patel 1115 (holotype: K! [K001588346]).

http://www.ipni.org/n/urn:lsid:ipni.org:names:77342881-1

Twining herb, presumably perennial, urticating, at least 40 cm long, monoecious. Stems branched, indumentum a mixture of non-urticating, short curved soft hairs < 1 mm and longer and stiffer non-urticating, spreading hairs to 3 mm with a bulbous base. Stipules persistent, 8 – 15 × 5 – 10 mm, ovate-cordate, acute, many-nerved from the base, subglabrous except regularly ciliate along margins with long stiff hairs. Leaves simple, alternate; blades 2 – 15 × 0.6 – 4 cm, ovate-lanceolate to lanceolate, acute at the apex, serrate to crenate-serrate on the margins, shallowly wide-cordate at the base, chartaceous, 3-veined from the base; more or less evenly hairy with an indumentum of long stiff non-urticating hairs with a bulbous base, hairs sparse but more abundant than on stipules, most abundant along midrib and main veins on both sides of the lamina; lateral veins 3 – 5 pairs, weakly prominent above, prominent beneath; laminar glands absent; petioles 5 – 15 mm long, hairs abundant. Inflorescences spikelike, up to 16 cm long, with the peduncle up to 8 cm long, terminal, becoming leaf-opposed, consisting mostly of male flowers with 2 female flowers at the base, urticating hairs present. Male bracts with scattered glands, 2 – 4 mm long, narrowly ovate-lanceolate, with 1 flower; 2 bracteoles on either side, 1 mm long, linear-lanceolate; bracts and bracteoles free, inserted at the base of the male flower pedicel. Female bracts resembling the male bracts. Male flowers: pedicels 1 mm long; calyx lobes 3, 1.5 mm long, elliptic, apiculate, cucullate, hairs sparse abaxially; nectaries absent; stamens 3; filaments 1 × 0.15 mm; anthers 2-celled, dorsifixed, introrse, the cells parallel and 0.22 × 0.15 mm; pistillode not seen. Female flowers subsessile; calyx lobes 3, 5 × 5 mm at the flowering stage, accrescent to 10 × 10 mm in fruit, each lobe palmately 15 – 17 lobulate, the lobes linear, lower lobes longer than the width of the calyx-lobe rachis, upper lobes shorter than the width of the calyx-lobe rachis; hairs dense, especially along margins, many urticating; calyx lobe rachis broadly ovate-suborbicular, hairy abaxially, glabrous adaxially, becoming hardened and whitish adaxially; ovary 2 mm in diam., 3-locular with 1 ovule per locule, hairs dense, many urticating; styles 3, 3 – 5 mm long, connate for half their length, hairs sparse; stigmas ± smooth, spreading. Fruit capsules, 7 × 12 mm, 3-lobed, smooth, hairs abundant, many urticating; calyx lobes persistent after dehiscence; styles persistent in fruit, caducous after dehiscence; columella soon caducous after dehiscence, 3-fid. Seeds 5 mm in diam., subglobose, grey, streaked and flecked with dark purplish-brown, with abundant white papillae near the hilum, ecarunculate. Fig. 1.

Fig. 1.
figure 1

Tragia grandistipularis. A habit; B leaf margin, abaxial surface; C stipule; D inflorescence rachis indumentum showing both urticating (short) and non-urticating hairs (long); E inflorescence; F male bracts and flowers; G male flower; H female flower sepal, enclosing flower; J fruit, separating from sepals, dehiscing; K seed. From Chapama, Mphamba & Patel 1115. drawn by andrew brown.

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recognition. Most like Tragia stipularis in the large, persistent stipules > 5 mm long, plants twining, male bracts 1-flowered, sepals of female flowers 3, but differs in the larger stipules (8 – 15 × 5 – 10 mm vs 5 – 10 × 4 – 7 mm in T. stipularis), which are more symmetrical (ovate-cordate vs falcate-ovate to falcate-lanceolate), larger leaves (to 15 × 4 cm vs 6 × 3.5 cm), longer inflorescences (to 16 cm vs to 4 cm long), longer male bracts (2 – 4 mm vs 1.5 – 2 mm long) and larger female flower calyx lobes (accrescent to 10 × 10 mm in fruit vs accrescent to 7 × 7 mm in fruit).

distribution. Only known from the type locality in the Chilwa-Phalombe plain, within the Phalombe District in the Southern Region of Malawi.

habitat. The species is known only from a single collection in a wooded grassland habitat within the Zambezian Flooded Grasslands system (Dinerstein et al. 2017). This highly dynamic ecosystem experiences seasonal cycles of flooding and drying driven by monsoonal rainfall patterns. The grassland where Tragia grandistipularis occurs is situated on the Chilwa-Phalombe terrace, an extensive plain formed by lacustrine and alluvial deposits, near the seasonal Noji stream (Kalk et al. 1979; Rivett et al. 2020). The specimen label indicates that the plant was growing in association with other wooded grassland species, such as Lonchocarpus capassa Rolfe, Bauhinia petersiana Bolle, and Combretum imberbe Wawra. T. grandistipularis may inhabit a habitat prone to at least periodic inundation, but further study is needed to confirm the local flooding regime and hydrological conditions.

conservation status. Tragia grandistipularis is only known from the type specimen collected in 2014, and no additional data exists to estimate its full distribution range. According to the seed-collecting data sheet information in the Millennium Seed Bank (MSB) database, the collectors found over 50 plants in the population. The species grows in the Chilwa-Phalombe terrace, a plain of lacustrine origin that slopes from the Mulanje Massif to the Lake Chilwa basin. The population occurs within the Lake Chilwa Wetland Biosphere Reserve, a UNESCO site, and the Lake Chilwa Ramsar site. However, this area faces several threats from human activities, such as population pressure, land degradation, deforestation, water pollution, invasive species, and climate change (Environmental Affairs Department 2006, 2015; Rivett et al. 2020). These threats could affect the survival and reproduction of the new species and its habitat quality and availability.

If this population is the only extant one, the species would qualify as Endangered (EN) under criterion D (number of mature individuals between 50 and 250) of the IUCN Red List Criteria (IUCN 2012). However, given that the species is known from a single locality, that its known extent of occurrence is below 100 km2, and that it faces the aforementioned threats, it also qualifies as Critically Endangered (CR) under criteria B1ab(i,ii,iii,v) according to the guidelines (IUCN 2022). Therefore, we provisionally assign the new species an IUCN conservation status of Critically Endangered [CR B2ab(i,ii,iii,v)]. We recommend further surveys to confirm the distribution and population size of the species, as well as conservation actions to protect its habitat and reduce threats.

Seeds from this population were collected and are now preserved as an accession at the MSB, along with some that may be stored at FRIM, providing an ex-situ conservation backup. However, of the 169 seeds held at the MSB, only 8 are potentially viable, as 19 out of the 20 that were tested were infested. Unfortunately, for collections smaller than 250 seeds, germination tests to determine viability are not conducted, to protect the remaining collection (Davies et al. 2022), and the current quantity of potentially viable banked seeds is too low to have an immediate, significant conservation impact. Seeds of Tragia ramosa Torr. germinated well, initially, at the MSB, but the long-term behaviour of seeds for the genus in storage remains unknown. To successfully conserve T. grandistipularis ex-situ, additional wild populations must be located to supplement the existing seed collection. The goal should be to collect a minimum of 500 potentially viable seeds, but no more than 20% of the mature seeds present at any one time, to allow sufficient seeds to remain for natural regeneration (Way & Gold 2022). For critically endangered species with small population sizes, like this one, it is crucial to maintain separate seed lots from individual parent plants during collecting. If future ex-situ propagation becomes necessary, to increase the seed reserves, plants grown from these distinct maternal lines can then be cross-pollinated to maximise genetic diversity (Way & Gold 2022).

phenology. Collected with both flowers and fruits in March. Southern Malawi experiences a distinct wet season from November to April driven by monsoonal rains. March falls within the peak of the wet season when low-lying areas experience flooding from the overflow of rivers and high rainfall. Additional observations of the species and its habitat would help determine whether its reproductive pattern is linked to these environmental factors.

etymology. Tragia grandistipularis is named for its large stipules, which are the largest among all known African Tragia species. The specific epithet is derived from the Latin words “grandis”, meaning “large”, and “stipularis”, meaning “pertaining to stipules”.

notes. Tragia grandistipularis is a very distinct species, differing from all other African Tragia species on account of the remarkably big stipules (see Fig. 1C). This character previously distinguished T. stipularis from all other African species, but T. grandistipularis has even bigger stipules (8 – 15 × 5 – 10 mm vs 5 – 10 × 4 – 7 mm), which are less asymmetrical (ovate-cordate vs falcate-ovate to falcate-lanceolate) (see Fig. 2). None of the other species of Tragia described in Flora Zambesiaca and Flora of Tropical East Africa has stipules that reach a length of 10 mm (Radcliffe-Smith 1987, 1996). In addition to this character, and those mentioned in the new species diagnosis above, T. grandistipularis also differs from T. stipularis in the higher abundance of stiff spreading hairs up to 3 mm long along the stems, petioles, and peduncle, giving the plant an overall more hirsute appearance (see Figs 1A & 2). Its leaves also tend to be narrower than in T. stipularis, which has more broadly triangular leaves, especially in the type specimen from Tanzania (mostly 3.5 × longer than wide in T. grandistipularis vs mostly 1.5 × longer than wide in T. stipularis). T. stipularis is not known to occur in Malawi but is found in southern Zambia.

Fig. 2.
figure 2

Key diagnostic characters of Tragia stipularis (left) and T. grandistipularis (right), showing differences in stipule size and stem indumentum. Ruler graduations in mm. Specimens: T. stipularis, Tanner 1539 (holotype, K); T. grandistipularis, Chapama, Mphamba & Patel 1115 (holotype, K).

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No records of Tragia in the Phalombe District are available in Flora Zambesiaca (Radcliffe-Smith 1996), the Flora of Malawi website (Hyde et al. 2024), or GBIF.org (2024). However, the second author found two previous collections of Tragia specimens in the district at MAL: T. kirkiana, collected from Machemba Hill (15°43'S 35°39'E, 15 Jan. 1991, Magombo 208B), and T. okanyua, collected from Sambani Forest Reserve (17 Oct. 1983, Seyani & Tawakali 1613). These specimens were originally labelled as from the Mulanje District, which included the Phalombe District until June 1998. The second author examined these specimens and measured their stipules, confirming that they are not additional collections of T. grandistipularis. T. kirkiana and T. okanyua differ from T. grandistipularis in their short, lanceolate stipules. In addition, T. kirkiana has 11 – 13-lobulate female-flower sepals (vs 15 – 17 lobulate, see Fig. 1H), and T. okanyua has leaves that are lobed at the base (vs unlobed, see Fig. 1A) and female flowers with 6 sepals (vs 3). Another species, T. adenanthera, was recorded nearby, in the Zomba District. It differs from T. grandistipularis not only in having short, lanceolate stipules but also notably in the longer male flower pedicels up to 2 mm long (vs 1 mm in T. grandistipularis) and conspicuously glandular male bracts. These bracts have abundant minute, sessile, globular glands, much less than 1 mm in diam. While such glands are also present in T. grandistipularis, they are less numerous and less visible.

The type specimen, which lacks the basal portion of the stem, is approximately 40 cm long, but information about the plant’s length and rootstock was not recorded in the field. These would provide additional information on the habit and ecology of this species.

The label on the holotype states that a duplicate is deposited at FRIM. However, the second author could not locate the isotype of Tragia grandistipularis at FRIM, despite a thorough search of all the collections of specimens made during the Millennium Seed Bank Project which are currently deposited there. The second author did not find any duplicates of the type specimen at MAL either.

Tragia grandistipularis belongs to Tragia sect. Tagira, a diverse and species-rich lineage of over 80 species widely distributed in Africa, Madagascar and South/West Asia. The greatest diversity is in dry regions of Africa, on account of its pinnatifid, pistillate sepals (see Fig. 1H), and to a lesser extent by the partially connate styles and staminate flowers with well-developed filaments (Cardinal-McTeague & Gillespie 2016, see Fig. 1G). Tragia sect. Tagira is paraphyletic and placed in Tragiinae Subclade T3, which also includes species of Tragiella and Tragia sect. Agirta. Based on molecular results, the current circumscriptions of Tragia sects. Agirta and Tagira and Tragiella are not supported, although resolution and node support need improvement before taxonomic boundaries are revised (Cardinal-McTeague & Gillespie 2016).

Supplement to the Key to Tragia in Flora Zambesiaca (Radcliffe-Smith 1996)

To insert Tragia grandistipularis in the Flora Zambesiaca (Radcliffe-Smith 1996: 216 – 218) key requires a couplet following the selection of male bracts 1 (2)-flowered, sepals of female flowers 3, and plants with stems twining at least at the top. The key is here amended from couplet numbers 26 (distributions added) to 27 and a new couplet is inserted at 27’, with characters to differentiate T. stipularis.

  • 25. Plant erect.............................................................................................................................................................................................................26

  • – Plant with stems twining at least at the top...............................................................................................................................................................................................................27

  • 26. Leaves not lobed (Zimbabwe)..........................................................................................................................................................................................................T. gardneri

  • – Leaves 3-lobed at the base (Zimbabwe, Southern Africa).............................................................................................................................................................................................................T. dioica

  • 27. Stipules ovate-cordate or falcate, 5 – 15 mm long..............................................................................................................................................................................................................27’

  • – Stipules lanceolate, 2 – 7 mm long..............................................................................................................................................................................................................28

  • 27’. Stipules falcate, 5 – 10 mm long. Plants puberulous and weakly hirsute, with few spreading hairs c. 1 mm long. Leaves mostly 1.5 × longer than wide (Uganda, Tanzania, Zambia).............................................................................................................................................................................................................T. stipularis

  • – Stipules ovate-cordate, 8 – 15 mm long. Plants covered with stiff spreading hairs up to 3 mm. Leaves mostly 3.5 × longer than wide (Malawi)............................................................................................................................................................................................................T. grandistipularis sp. nov.

Flora Zambesiaca Key continues at couplet 28.