Solanum subgenus Leptostemonum Bitter, the Leptostemonum Clade

Description.

Herbs, vines, scandent or prostrate shrubs, shrubs or small trees; armed or apparently (to almost completely) unarmed; young stems stellate-pubescent, the trichomes multangulate or more often porrect-stellate with the rays all in a single place, occasionally lepidote, sometimes glabrescent; prickles absent, sparse or dense, straight or curved; bark of older stems grey or brown, sometimes glabrescent. Sympodial units plurifoliate or difoliate, the leaves geminate or not. Leaves entire to deeply pinnately lobed, usually stellate-pubescent on both surfaces, sometimes glabrescent or the trichomes very sparse; pubescence of porrect, multangulate or lepidote stellate trichomes, these sessile or variously stalked, with or without midpoints, the midpoints if present very short and bump-like to elongate. Inflorescences lateral and internodal or opposite the leaves, unbranched to many times branched, usually pedunculate, not bracteate, variously stellate-pubescent; petioles articulated near the base. Flowers actinomorphic or zygomorphic, bisexual (hermaphroditic) or unisexual and the plants andromonoecious; calyx 5-parted (rarely 4-parted or more than 5-parted in cultivated forms of S. melongena), usually stellate-pubescent, sometimes glabrescent; corolla 5-parted (rarely 4-parted or more than 5-parted in cultivated forms of S. melongena), rotate-stellate to deeply stellate, white, lilac or deep purple, some species polymorphic for flower colour, interpetalar tissue absent to copious; stamens 5 (rarely 4 or more than 5 in cultivated forms of S. melongena), the filaments equal or unequal, usually glabrous; anthers equal or unequal, yellow or cream, blunt to strongly tapered, tightly connivent or spreading, dehiscing by terminal pores, the pores usually not lengthening to slits with age; ovary bicarpellate (fasciated in cultivars of S. melongena), globose to conical, glabrous or stellate-pubescent; style straight or curved, in andromonoecious species shorter than the anthers and held within the anther cone; stigma minutely to large-capitate or clavate, sometimes bilobed. Fruit a berry, usually globose or nearly globose (but variously shaped in S. mammosum and S. melongena), the pericarp dry, fleshy or leathery, glabrous or stellate-pubescent, the surfaces shiny or matte; fruiting calyx lobes not enlarging or often accrescent, sometimes completely enclosing the berry. Seeds flattened-reniform, the testal cells sinuate or polygonal in outline. Chromosome number: n = 12, 24, 36 (see Scaldaferro et al. 2012).

Distribution.

Members of the Leptostemonum Clade are found worldwide, in all habitats but the group is most diverse in the tropics (see Whalen 1984; Bohs 2005; Gagnon et al. 2022). They are often weedy plants of disturbed areas.

Discussion.

The Leptostemonum Clade is the largest monophyletic group in the genus Solanum . The clade is characterised by the possession of stellate trichomes (sometimes modified), prickles (sometimes absent) and long-attenuate, tapering anthers with distally directed pores that do not elongate to laterally dehiscing slits (as do those of other groups of Solanum, see Knapp et al. 2019a). Here we have chosen to treat the species occurring in tropical Asia as a group to fill a significant gap in the understanding of the species level taxonomy of spiny solanums. As for other geographically based groupings in spiny solanums, Asian members of the Leptostemonum Clade do not form a monophyletic assemblage (e.g., Aubriot et al. 2016a; Vorontsova and Knapp 2016); when the species treated have been included in phylogenetic studies, their hypothetical evolutionary relationships are provided in species discussion sections. For further discussion and previous assignments of the taxa treated here to species groups see sections on Taxonomy and Phylogeny above and Table 1.

We have cited types but not reproduced synonymy and complete descriptions of the introduced species here; these can be found in the cited monographic works and on Solanaceae Source. Several of these names are lectotypified here because they were incorrectly cited as having holotypes in previous works. We have cited all synonyms based on specimens from tropical Asia. Many of these introduced taxa are expanding in range with increased disturbance and environmental damage, so the distribution given in Table 2 is what we know now; we expect some of these to be found elsewhere in the future.

Artificial key to tropical Asian spiny solanum species (including non-native adventive taxa)

Artificial key to all species

Synoptic character list for tropical Asian spiny solanums

This synoptical character list can be used as a multi-entry key for identification. We have only listed diagnostic characters here, for example, entire and pinnatifid leaves are listed but not lobed leaves in general. For distributional information please see Table 2. The list is intended to be used as a tool via a process of elimination; any character can be selected and in combination with other characters, a smaller selection of species can be obtained, for which the descriptions will be useful for coming to a final identification.

Plants found in cultivation (agricultural settings or home gardens): aethiopicum, macrocarpon, mammosum, melongena

Scrambling or prostrate plants: cordatum, cyanocarphium, forskalii, miyakojimense, procumbens, schefferi, trilobatum, wightii

Plants unarmed (no obvious prickles anywhere on plant): aethiopicum, camranhense, comitis, cordatum, deflexicarpum, dunalianum, giganteum, lasiocarpum, macrocarpon, melongena, miyakojimense, nienkui, peikuoense, pubescens, putii, retrorsum, robinsonii, torvoideum, torvum, vagum, violaceum, wrightii

Plants drying black on herbarium specimens: giganteum, kachinense, poka, pseudosaponaceum

Plants andromonoecious (with basal hermaphroditic and distal staminate flowers): arundo, barbisetum, insanum, lasiocarpum, macrocarpon, melongena, schefferi, virginianum, wightii

Small trees, taller than 3 m: arundo, chrysotrichum, (comitis?), dunalianum, giganteum, peikuoense, pseudosaponaceum, torvoideum, wrightii

Simple trichomes (never stellate) on stems: aculeatissimum, capsicoides, mammosum, viarum

Stems white from dense pubescence of multangulate stellate trichomes: arundo, forskalii, giganteum

Stems with strongly hooked prickles: cordatum, cyanocarphium, graciliflorum, jamaicense, procumbens, schefferi, trilobatum

Stem prickles straight and strongly retrorse: retrorsum

Rays of stellate trichomes fused at the base (lepidote or almost lepidote): elaeagnifolium, robinsonii

Trichomes and/or prickles purple or purplish black in live plants (sometimes also visible on herbarium specimens): barbisetum, cyanocarphium, hovei, involucratum, lasiocarpum, praetermissum (insanum and melongena prickles purple only)

Leaves on reproductive branches <1.5 times longer than wide: camranhense, cordatum, forskalii, involucratum, lasiocarpum, miyakojimense, praetermissum, pubescens, sulawesi, trilobatum, virginianum, wightii

Leaves on reproductive branches entire (without lobes): camranhense, comitis, cordatum, dunalianum, elaeagnifolium, forskalii, giganteum, miyakojimense, nienkui, poka, praetermissum, procumbens, pseudosaponaceum, pubescens, putii, retrorsum, robinsonii, schefferi, torvum, vagum

Leaves on reproductive branches with secondary lobing (some lobing to pinnatisect): arundo, multiflorum, sisymbriifolium, violaceum, virginianum

Leaves glabrous or glabrescent adaxially: aethiopicum, arundo, cordatum, giganteum, graciliflorum, kachinense, macrocarpon, melongena (rarely), peikuoense, retrorsum, trilobatum, vagum, virginianum

Leaves with bright yellow, straight prickles> 1 cm long: aculeatissimum, arundo, capsicoides, sulawesi, virginianum

Leaves with only simple trichomes adaxially: aculeatissimum, capsicoides, mammosum, viarum, wrightii

Pubescence of adaxial leaf surfaces of multangulate trichomes with all rays pointing upwards: comitis

Pubescence of white mealy multangulate trichomes that are easily rubbed off: giganteum, vagum

Leaf bases decurrent onto the stem: macrocarpon, robustum

Leaf bases cordate/truncate: camranhense, cordatum, forskalii, melongena, pubescens, wightii

Inflorescence many times branched: dunalianum, giganteum, graciliflorum, harmandii, kachinense, multiflorum, peikuoense, pseudosaponaceum, schefferi, torvoideum

Inflorescence glandular pubescent: aculeatissimum, pubescens, torvum, viarum

Peduncles absent or very short (<5 mm): cordatum, miyakojimense, sulawesi, torvoideum, violaceum, wightii

Calyx lobes foliaceous: macrocarpon, melongena, robustum

Calyx lobes with a distinct acumen: camranhense, peikuoense, poka, robinsonii, torvoideum, vagum, virginianum

Corolla stellate-rotate or pentagonal (with abundant interpetalar tissue): comitis, insanum, macrocarpon, melongena, virginianum, wightii

Corolla deeply stellate (lobed nearly to the base): barbisetum, graciliflorum, kachinense, retrorsum, schefferi, vagum

Anthers unequal (even slightly so): nienkui, procumbens, pubescens, putii, robinsonii, vagum, wightii

Anthers with several markedly different in size and shape, strongly curved: pubescens, vagum, wightii

Calyx strongly accrescent in fruit, more than half covering the berry: barbisetum, cyanocarphium, involucratum, macrocarpon, praetermissum, wightii

Immature berries marbled green and white: aculeatissimum, arundo, insanum, jamaicense, miyakojimense, viarum, virginianum

Mature berry> 3 cm in diameter: aethiopicum, arundo, lasiocarpum, macrocarpon, mammosum, melongena, schefferi, wrightii

Mature berries not strictly globose: hovei, macrocarpon, mammosum, melongena, miyakojimense, schefferi

Mature berries red or orange, thin-skinned and fleshy (usually juicy): camranhense, cordatum, deflexicarpum, dunalianum, forskalii, giganteum, hovei, involucratum, jamaicense, lasiocarpum, miyakojimense, multiflorum, nienkui, peikuoense, procumbens, pseudosaponaceum, pubescens, retrorsum, robinsonii, sisymbriifolium, trilobatum, vagum, violaceum

Mature berries bright yellow when ripe: aculeatissimum, arundo, insanum, violaceum, virginianum

Mature berries greenish yellow or yellowish green when ripe: chrysotrichum, insanum, melongena, poka, torvoideum, torvum, torvoideum, wightii (just before dehiscence)

Mature berries white or greenish white when ripe: barbisetum, praetermissum

Mature berries black or purple when ripe: melongena, peikuoense, torvoideum

Mature berries leathery: aculeatissimum, arundo, capsicoides, chrysotrichum, elaeagnifolium, insanum, macrocarpon, mammosum, melongena, viarum, virginianum, wrightii

Mature berry dry, pseudo-capsular or the pericarp shattering: elaeagnifolium, wightii

Mature berries densely and uniformly pubescent: involucratum, lasiocarpum, robustum, sulawesi

Inner flesh of berry spongy and not at all juicy: capsicoides, mammosum, melongena

Seeds> 100 per berry: cyanocarphium, insanum, involucratum, lasiocarpum, poka, pseudosaponaceum, schefferi, sulawesi, torvoideum, virginianum, wrightii

Seeds 10 or fewer per berry: camranhense, cordatum, forskalii, graciliflorum, hovei, multiflorum, nienkui, procumbens, retrorsum, robinsonii, vagum, violaceum

Seeds dark brown or blackish brown: cordatum, forskalii

Seeds with a distinct wing: capsicoides

Species descriptions