Madagascar. Toliara: Forêt de Zombitsy (Sakaraha), aux confins des basins du Fiherenana et de L’Onilahy, forêt tropophile sur sables siliceux de l’Isalo, 26-29 March 1955, 600-850 m, H. Humbert, L. Bègue & R.P.R. Capuron 29654 (holotype: P [P00349299]; isotypes: K [K000414193], MO [MO-150886]).

Subshrub or shrub to canopy liana, of extremely variable height. Stems terete, finely dendritic pubescent at the tips, glabrescent. New growth unevenly pubescent, with densely branched dendritic to echinoid uniseriate trichomes ca. 0.2 mm long. Bark of older stems smooth, almost white to brown, glabrous. Sympodial units plurifoliate, the leaves not geminate, evenly distributed along young branches and clustered on short shoots on older plants. Leaves simple, 3-4.5 cm long, 1.2-2(3) cm wide, ovate to elliptic, rarely obovate, membranous to chartaceous, concolorous to weakly discolorous, both surfaces glabrous or pubescent with dendritic trichomes ca. 0.1 mm long; major veins 5–7 pairs, spreading at ca. 45° to the midvein and forming loops, the finer venation a prominent network of fine brown veins visible abaxially in herbarium specimens; base cuneate to truncate; margins entire or with up to 2 pairs of lobes in the lower half and with sinuses halfway to the midrib, the lobes rounded at the tips; apex acute to rounded; petiole 0.7–1.5 cm long, slender, densely dendritic-pubescent like young stems, glabrescent. Inflorescences terminal on short shoots, 2–5 cm long, unbranched or furcate, with 1–3 flowers, evenly dendritic-pubescent, the trichomes 0.1–0.2 mm long; peduncle absent or up to 2.5 cm long; pedicels ca. 1.5 cm long, apically dilated, ridged when dry, evenly dendritic-pubescent like the rachis, articulated 0–0.5 mm from base; pedicel scars irregularly spaced 1–5 mm apart, prominent. Buds ellipsoid, the corolla only just emerging from the calyx tube before anthesis, the tip of the bud shorter than the calyx lobes. Flowers 5-merous, apparently all perfect. Calyx tube 2–3 mm long, cup-shaped, the lobes 2–3 mm long, 1.5–2 mm wide at base, unevenly deltate, acute, evenly pubescent with dendritic trichomes like those of the rest of the inflorescence, with simple uniseriate trichomes up to 0.2 mm long on the margins. Corolla 1.2–2 cm in diameter, violet, stellate, lobed almost to base, the lobes 5–10 mm long, 2–3 mm wide, ovate to narrowly triangular, glabrous adaxially, sparsely pubescent abaxially, more densely pubescent at the tips with translucent, simple and/or dendritic trichomes. Stamens equal; filament tube ca. 1 mm long; free portion of the filaments 1–2 mm long, glabrous; anthers 3.5–4 mm long, ca. 1.5 mm wide, broadly oblong or ellipsoid, loosely connivent, smooth abaxially, poricidal at the tips, the pores much smaller than anther apices, ca. 0.4 mm in diameter, clearly delineated and not lengthening with age. Ovary conical, glabrous; style 7–8 mm long, protruding 2–3 mm beyond the anthers, curved, glabrous; stigma clavate, dark, the surface minutely papillose. Fruit an elongated ovoid berry, ca. 1.3 cm long, ca. 1 cm in diameter (immature?), apically pointed, the pericarp thin, glabrous; fruiting pedicels 1.5–3 cm long, ca. 0.8 mm diameter at base, pendent, ridged; fruiting calyx slightly accrescent, the lobes to ca. 5 m long, ca. 4 mm wide and forming a loose cup around the developing fruit. Seeds not known.

(Figure 6). Endemic to Toliara province in southern Madagascar.

Open dry forest and scrub on limestone or sand; 600–1100 m elevation.

None recorded.

(IUCN 2014).

Least Concern

Solanum betroka is a spindly shrub or liana endemic to southern Madagascar. It has small membranous lobed leaves with prominent finer venation clustered on the tips of branches, no more than 3 flowers per inflorescence, and no tufts of trichomes in the axils of the major leaf veins on leaf undersides (domatia). It is the only species of Solanum endemic to Madagascar not a member of the Leptostemonum clade to commonly exhibit lobed leaves (Fig. 5) on reproductive stems; lobed leaves in Solanum madagascariense occasionally occur but are rare.

Solanum betroka can be difficult to distinguish from the very similar and possibly closely related Solanum sambiranense and Solanum imamense. It differs from Solanum sambiranense by its ovate to elliptic (versus elliptic to obovate) leaves under 5 cm (versus over 5 cm) long, with cuneate to truncate (versus attenuate) bases, inflorescences with 1–3 (versus 3–10) flowers, and calyx lobes 2–3 mm (versus 4–6 mm) long. Solanum betroka bears a strong resemblance to Solanum sambiranense: both have a clearly visible brown fine venation network, membranous glabrescent leaves that dry greenish brown, and a similar habit. Typical representatives of the southern Solanum betroka and northern Solanum sambiranense are clearly distinct but specimens from the centre of Madagascar are more difficult to determine. Further sampling may prove that these two taxa are in fact conspecific. Solanum betroka can be distinguished from Solanum imamense by its inflorescences with 1–3 (versus 7–13) flowers, flowers under 2 cm (versus over 2 cm) in diameter, and anthers 3.5–5 mm (versus 4–5 mm) long.

Solanum betroka has also been confused with unarmed specimens of the spiny solanums Solanum batoides D’Arcy & Rakot. and Solanum erythracanthum Dunal; these can be distinguished easily based on pubescence and anther morphology. Solanum betroka has dendritic trichomes and ellipsoid anthers while Solanum batoides and Solanum erythracanthum have the stellate trichomes and long-tapered anthers typical of members of the Leptostemonum clade (Vorontsova et al. 2013; Vorontsova and Knapp 2016).

Solanum betroka occurs primarily in the unique arid southern ecoregion of Madagascar, with a few records further north in the somewhat wetter western ecoregion (Humbert 1955; Faramalala 1988, 1995). It is the only member of the African non-spiny clade restricted to such severely dry climate, although a few spiny Solanum species also occur in the area: Solanum batoides, Solanum bumeliifolium Dunal, Solanum croatii D’Arcy & R.C.Keating, and Solanum heinianum D’Arcy & R.C.Keating; the related Solanum imamense is partly sympatric with Solanum betroka in the wetter more northern parts of its distribution range. The habitat niche of Solanum betroka is significantly different from that of Solanum imamense and Solanum sambiranenese both of which occur in wetter habitats further north.. The type collection has smaller leaves with more lobes and denser indumentum than the majority of specimens, and does not exhibit the characteristic pronounced brown venation on dry leaves.

Madagascar. Toliara: Tulear-Ihosy km 44, 12 Nov 1967, Bernardi 11407 (G, P); environs de Betroka, Feb 1963, Bosser 17370 (K, MO, P, TAN); Ambovombe, 2 Feb 1926, Decary 3729[a] (MO, NY); Taolagnaro (F-Dauphin), Angavo, massif de l’Angavo á l’Est d’Antanimora, 16 Jul 1926, Decary 4443 (K, MO, P); Amboasary-Sud, Ampasimpolaka à l’est d’Ambovombe, 29 Jun 1931, Decary 9046 (MO, P); Bekily, Ampandrandava, 1943, Herb Jard Bot Tananarive 6083 (P); Zombitsy, Forêt de Zombitsy (Sakaraha) aux confins des bassins du Fiherenana et de l’Onilahy, Mar 1955, Humbert et al. 29627 (K, MO, NY, P); 57 km de Tulear, P.K. 888, 23 Oct 1966, Leroy 3 (P); Forêt de Zombitse [Zombitsy], 13 Apr 1961, Peltier & Peltier 3069 (P, TAN); Bekily, environs d’Ampandrandava (entre Bekily et Tsivory), Nov 1942, Seyrig 371 (MO, P).