A new species of Solanum (Solanaceae) from South Africa related to the cultivated eggplant

Abstract A new andromonoecious species related to the eggplant and belonging to Solanum subgenus Leptostemonum from southern Africa is described. Solanum umtuma Voronts. & S.Knapp, sp. nov. is found in the eastern part of South Africa, and is sympatric with its close relative Solanum linnaeanum Hepper & P.M-L.Jaeger. It is morphologically very similar to Solanum cerasiferum Dunal of northern tropical Africa. A comparison table with similar and closely related species is provided, as are a distribution map and illustration of Solanum umtuma.


Introduction
Th e Solanaceae is an economically important, cosmopolitan family with approximately 3000 species in some 90 genera. Th e Solanaceae include globally important food crops such as the cultivated potato (Solanum tuberosum L.), tomato (S. lycopersicum L.), aubergine (S. melongena L.), and chilli pepper (Capsicum spp.) as well as a number of widely used drug plants such as tobacco (Nicotiana tabacum L.), Datura, and Atropa belladonna L., the source of atropine. Th e giant genus Solanum L. with ca. 1500 species has become a model system for collaborative online taxonomy in challenging tropical plant groups (see Knapp et al. 2004 and http://www.solanaceaesource.org). Many new species of Solanum have been described as part of the PBI (Planetary Biodi-versity Inventory) Solanum project (e.g. Knapp 2010;Vorontsova et al. 2010aVorontsova et al. , 2010bVorontsova and Mbago 2011) that aims to produce a complete species-level on-line monograph of the genus. In the course of work on the prickly solanums in Africa and Madagascar we discovered the new species described here.
Th e "spiny" (or more accurately prickly) solanums (Solanum subgenus Leptostemonum Dunal) are the largest clade in the genus, with some 750 species (Whalen 1984;Bohs 2005). Most species in subgenus Leptostemonum are found in the New World, but approximately 150 species occur in the Old World, including taxa from Africa, Asia, and Australia. Th ese Old World species form a monophyletic clade (see Levin et al. 2006;Weese and Bohs 2010). In the Old World clade of prickly solanums, the wild relatives of the cultivated eggplant (or aubergine) S. melongena are one of the most variable and confusing groups. Th ey have been classifi ed as Solanum section Melongena (Mill.) Dunal (Bitter 1923) or the Solanum incanum species group (Whalen 1984), and many taxa, both at the specifi c and infraspecifi c rank, have been described for these variable plants.
Although the eggplant is generally considered to be a vegetable of Asian origin and distribution (see Wang et al. 2008), it is a member of a predominantly African clade within the prickly solanums (Weese and Bohs 2010). In addition to S. melongena (including S. ovigerum Dunal) the "wild eggplants" currently include seven species of prickly subshrubs native to Africa and Asia: Solanum aureitomentosum Bitter, S. campylacanthum Hochst. ex A.Rich. (including S. panduriforme Dunal and S. delagoense Dunal), S. cerasiferum Dunal, S. incanum L., S. insanum L. (including S. cumingii Dunal), S. lichtensteinii Willd., and S. linnaeanum Hepper & P.-M.L.Jaeger (for complete synonymy of these taxa see the Solanaceae Source website, http://www.solanaceaesource.org; complete synonymy will also be included in the upcoming monograph). Th ese species are all bushy erect subshrubs 0.5-2 m tall with lobed leaves, an andromonoecious breeding system with 1(-3) larger hermaphrodite fl owers at the base of every infl orescence and smaller functionally male fl owers at the distal parts of infl orescences, 1(-3) large yellow fruits, and variable pubescence composed of stellate trichomes. Th ey occupy similar ecological niches throughout their respective ranges (see Table 1 for a comparison of the accepted species in this group) and usually are found growing in open disturbed areas between sea level and approximately 2000 m elevation. Complex species boundaries and high levels of morphological variability have led to much confusion between these species of eggplant relatives, and all of them have been placed in Solanum incanum sensu lato at one time or another (e.g., in fl oristic works such as D' Arcy and Rakotozafy 1994;Gonçalves 2005), with the exception of the morphologically quite distinct S. linnaeanum with rounded leaf lobes that has historically been called "S. sodomeum L." (Hepper and Jaeger 1986). Solanum linnaeanum is probably native to southern Africa although it is a common weed in North Africa and southern Europe.
Work on species limits in the eggplant group was carried out by the late Richard Lester's students (Jaeger 1985;Hasan 1989;Lester and Hasan 1991;Samuels 1994Samuels , 1996 using morphological and biosystematic methods. Molecular phylogenetic re- Table 1.

Morphological diff erences between
Solanum umtuma and other eggplant relatives in Africa. Calyx characters refer to the long-styled fl owers at the base of the infl orescence and not to the smaller, functionally male, short-styled fl owers in the distal parts of the infl orescence. Th is comparison focuses on the characters relevant to the identifi cation of S. umtuma and does not include all the characters useful for separating the other members of this group (these will be presented in an up-coming monographic treatment of the prickly solanums of Africa and Madagascar, Vorontsova and Knapp, in prep.). construction by Weese and Bohs (2010) confi rmed Lester's hypothesis (e.g., Mace et al. 1999) that the cultivated eggplant has its closest relatives in Africa, although few Asian members of the Old World clade were examined. As part of of a larger monographic project on the African prickly solanums, examination of collections from South Africa identifi ed a group of specimens distinct from the sympatric S. campylacanthum, S. lichtensteinii, and S. linnaeanum but with morphological similarity to the allopatric northern tropical African S. cerasiferum (Table 1). Preliminary molecular phylogenetic reconstruction using the nuclear ITS and waxy regions and the plastid trnT-F region confi rms that this morphologically identifi ed entity is distinct from S. cerasiferum and places it as sister to S. linnaeanum (S. Stern and L. Bohs, unpublished data). Th is new species is described here and the type selected from specimens in South African herbaria, following the recommendations of Smith and Figueiredo (2011). Description. Shrub, 0.5-1.5 m. Young stems erect, slender, moderately stellatepubescent to glabrescent, with porrect sessile or variously stalked trichomes, the stalks to 0.2 mm long, the rays 6-8, ca. 0.2 mm long, the midpoints approximately the same length as the rays, armed with straight prickles 3-4 mm long, 1-2 mm wide at base, deltate, fl attened, pale yellow-orange, glabrous, spaced 5-20 mm apart; bark of older stems glabrescent, green-brown to dark brown. Sympodial units plurifoliate. Leaves lobed; blades 8-20 cm long, 5-15 cm wide, 1.5-2 times longer than wide, elliptic, chartaceous, drying concolorous to weakly discolorous, green-brown, moderately stellate-pubescent on both surfaces, with porrect, sessile or stalked trichomes, the stalks to 0.2 mm long, the rays 6-8, 0.2-0.5(-0.8) mm long, the midpoints approximately the same length as the rays, with 5-20 prickles on both surfaces; the primary veins 4-6 pairs, the tertiary venation clearly visible abaxially and not visible adaxially; base  cuneate to truncate; margins lobed, the lobes 3-4 on each side, 1-3 cm long, deltate, apically obtuse to acute, extending approximately 1/3 of the distance to the midvein, often with secondary lobing; apex obtuse to acute; petiole 1-3 cm long, approximately 1/6 of the leaf blade length, moderately stellate-pubescent, with 0-5 prickles. Infl orescences apparently lateral, 3.5-9 cm long, rarely branched, with 6-15(-20) fl owers, 1-4 fl owers open at any one time, weakly stellate-pubescent, with 0(-5) prickles; peduncle 1-3 mm long; pedicels 1-2.3 cm long in long-styled fl owers, 0.8-1.2 cm long in shortstyled fl owers, erect to pendent, articulated at the base, moderately stellate-pubescent to glabrescent, with 0-20 prickles on long-styled fl owers, unarmed on short-styled fl owers; pedicel scars spaced 2-8 mm apart. Flowers 5-merous, heterostylous and the plants andromonoecious, with the lowermost 1-3 fl owers long-styled and hermaphroditic, the distal fl owers short-styled and functionally male. Calyx 11-22 mm long in long-styled fl owers, 5-9 mm long in short-styled fl owers, the lobes 7-10 mm long in long-styled fl owers, 3-4 mm long in short-styled fl owers, ovate and foliaceous in long-styled fl owers, deltate in short-styled fl owers, apically bluntly acute in long-styled fl owers and acute to obtuse in short-styled fl owers, moderately stellate-pubescent, with 30-80 prickles in long-styled fl owers and 0-30 prickles in short-styled fl owers. Corolla 2.5-3.3 cm in diameter in long-styled fl owers, 1.5-2.5 cm in diameter in short-styled fl owers, usually white or white with purple midveins, sometimes mauve, stellate, lobed for 1/4-1/2 of its length, the lobes ca. 7 mm long, ca. 10 mm wide in long-styled fl owers, 6-10 mm long and 5-8 mm wide in short-styled fl owers, broad-deltate, spreading, sparsely stellate-pubescent abaxially, the trichomes porrect, sessile or stalked, the stalks to 0.2 mm, the rays 5-8, 0.2-0.4 mm long, the midpoints approximately the same length as the rays. Stamens equal, with the fi lament tube 1-3 mm long, the free portion of the fi laments ca. 0.5 mm long; anthers 5-6 mm long in long-styled fl owers, 4.5-5.8 mm long in short-styled fl owers, connivent, tapering, poricidal at the tips. Ovary glabrous, with a few stellate trichomes towards the apex; style 1.1-1.2 cm long in long-styled fl owers, stout, straight or gently curved, moderately stellate-pubescent for most of its length. Fruit a spherical berry, 1(-2) per infructescence, 2.7-3.5 cm in diameter, the pericarp smooth, dark green with pale green and cream markings when young, yellow at maturity; fruiting pedicels 2-3 cm long, 1.2-2.2 mm in diameter at base, woody, pendulous, with 0-20 prickles; fruiting calyx not accrescent, covering 1/4-1/3 of the mature fruit, refl exed, with 10-80 prickles. Seeds ca. 100-200 per berry, 2.7-3.5 mm long, 2-2.5 mm wide, fl attened-reniform, orange-brown. Distribution (Fig. 3). End emic to South Africa in KwaZulu-Natal and Eastern Cape provinces (most specimens from KwaZulu-Natal); 50-1300 m elevation. Solanum umtuma is limited to the Maputaland-Pondoland Floristic Region (van Wyk and Smith 2001) and spans the Maputaland and Pondoland Centres of endemism.

Solanum umtuma
Ecology. Occasional on grassland, scrub, and forest edges, usually growing on sandy soil.
Etymology. "Umthuma" is an isiXhosa vernacular name for many species of prickly Solanum; in the Xhosa language the "th" is pronounced as "t", so we have here written the epithet phonetically as "umtuma". Th e epithet is used here as a noun is apposition and thus not latinized to agree in gender.
Preliminary conservation status. Solanum umtuma is a species of open and somewhat disturbed habitats (as are many prickly solanum species) and occupies an area of approximately 8000 km 2 and appears to be relatively evenly distributed within that area (Fig. 3). Although not normally common where it occurs, it is not a species of immediate conservation concern.
Selected specimens examined. South Africa. Discussion. Solanum umtuma is a medium-sized subshrub with straight prickles, acute to obtuse leaf lobes, and large yellow fruits. It is almost certainly a close relative of the sympatric S. linnaeanum; the two species share long, leafy, prickly calyx lobes on long-styled fl owers and fruits and diff er primarily in the shape of their leaf lobes. Solanum linnaeanum is immediately recognisable by its quite deeply incised leaves with rounded lobes; a few intermediate specimens of S. umtuma have somewhat rounded lobes, e.g. R.G. Strey 6750 (K000441991). Label data indicate that S. umtuma has white or only occasionally violet to mauve fl owers, while S. linnaeanum always has purple fl owers.
Solanum umtuma is morphologically very similar to S. cerasiferum and more superfi cially similar to other species with straight prickles and acute to obtuse leaf lobes, including the African highland S. dasyphyllum Schumach. & Th onn. (Solanaceae Source 2011) and S. robustum H.Wendl. of the New World (see Nee 1999). It is not sympatric with any of those species, so confusion is only possible in the herbarium. Solanum umtuma can be distinguished from S. cerasiferum by its cuneate to truncate leaf bases (versus short-attenuate leaf bases in S. cerasiferum), ovate foliaceous calyx lobes 7-10 mm long on long-styled fl owers (versus deltate to long-deltate membranous calyx lobes 4-7 mm long on long-styled fl owers in S. cerasiferum), and the densely spiny calyx of long-styled fl owers with ca. 30-80 prickles at anthesis (versus fl ower calyces with only 0-20 prickles at anthesis in S. cerasiferum). Solanum dasyphyllum and S. robustum both have leaf blades that are markedly attenuate on the petiole and decurrent onto the stem, the stems are usually somewhat winged from these decurrent leaf bases. Solanum umtuma is sympatric with S. lichtensteinii and diff ers from it by its obtuse to acute leaf lobes (versus rounded leaf lobes in S. lichtensteinii).
Specimens of Solanum umtuma have sometimes been annotated as "Solanum fuscatum L." or "Solanum ferrugineum Jacq." Th ese names are both widely misapplied. No original material of S. fuscatum L. has been located and the application of this name has been in doubt (Knapp and Jarvis 1990) and it has been proposed for rejection (Knapp 2011). Solanum ferrugineum Jacq. is the accepted name for a member of section Torva from the New World; this species occurs from Mexico to Costa Rica (Nee 1999;L. Bohs pers. comm.).