Solanum macrothyrsum Dammer, Bot. Jahrb. Syst. 38: 185. 1906.

Knapp, Sandra & Vorontsova, Maria S., 2016, A revision of the " African Non-Spiny " Clade of Solanum L. (Solanum sections Afrosolanum Bitter, Benderianum Bitter, Lemurisolanum Bitter, Lyciosolanum Bitter, Macronesiotes Bitter, and Quadrangulare Bitter: Solanaceae), PhytoKeys 66, pp. 1-142 : 47-50

Solanum macrothyrsum Dammer, Bot. Jahrb. Syst. 38: 185. 1906. Figure 15

Type.

Mayotte [French Overseas Department]: Maore (Grande Terre), forêt de Combani, 6 Nov 1884, L. Humblot 387 (second stage lectotype, designated here; first stage designated by D’Arcy & Rakotozafy 1994, pg. 100: P [P00184304]; isolectotypes: BM [BM000887183], P [P00184305], P [P00184306], P [P00184307], K [K000414185], W [W1889-0038295]) .

Description.

Liana of forest canopy, height unknown. Stems flexuous, terete, glabrous, green; new growth glabrous or minutely papillate, green; bark of older stems smooth, light grey. Sympodial units plurifoliate, the leaves not geminate, clustered at tips of branches. Leaves simple, (5)6-8 cm long, 3-4(4.5) cm wide, oblong to obovate, membranous to chartaceous, concolorous, glabrous on both surfaces, abaxially sometimes with isolated simple to dendritic trichomes along the midvein and with tufts of tangled simple or dendritic uniseriate trichomes in the axils of the main veins, the lamina texture somewhat altered under the tufts; major veins 4-6 pairs, prominent, spreading at ca. 40° to the midvein, the finer venation faint; base attenuate and decurrent onto the petiole; margins entire; apex acute to apiculate; petiole 1.5-4 cm long, slender, canaliculate, glabrous. Inflorescences terminal, at the apex of a long slender flexuous branch, 7-10 cm long, several times branched, with 15-50 flowers, glabrous; peduncle 4.5-7 cm; pedicels apically dilated, 0.5-0.8 cm long, glabrous except for the occasional simple or sparsely dendritic trichomes just below the articulation, articulated 0-0.5 mm from base; pedicel scars 1.5-8 mm apart, becoming closer together distally, somewhat peg-like. Buds globose, the corolla soon exserted from the calyx tube before anthesis. Flowers 5-merous, apparently all perfect. Calyx tube 1.5-2 mm long, broadly cup-shaped, the lobes ca. 0.5 mm long, 1-1.5 mm wide at base, broadly deltate, rounded to cuspidate at the tips, the sinuses scarious, glabrous with tufts of translucent simple hairs at the tips and sometimes extending along the margins. Corolla 1-2 cm in diameter, mauve to lilac or white with purple towards the centre, stellate, lobed almost to base, the lobes 6-12 mm long, 1.5-4 mm wide, narrowly ovate to obovate, cucullate, glabrous adaxially, with simple to dendritic trichomes sparsely distributed abaxially, denser towards the tips, the margins densely papillate with translucent-violet trichomes ca. 0.1 mm long. Stamens equal; filament tube ca. 1 mm; free portion of the filaments 1-1.5 mm long, glabrous; anthers 2.5-3 mm long, 1.5-2 mm wide, broadly ellipsoid, spreading or very 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 6-9 mm long, protruding 2-3 mm beyond the anthers, slightly curved, glabrous; stigma capitate, minutely papillose. Fruits and seeds not known.

Distribution

(Figure 16 ). Endemic to the island(s) of Mayotte (a political department of France geographically situated in the Comoro Islands); only recorded from the largest island Maore (=Mayotte or Grande-Terre).

Ecology and habitat.

Wet forests; 200 to 400 m elevation (calculated from locality information; elevation not recorded exactly on any specimens we have seen).

Common names and uses.

None recorded.

Preliminary conservation status

( IUCN 2014). Data Deficient (DD). Known from only two collections on the island of Mayotte collected 100 years apart (see below) with insufficient habitat information to assess its distribution. It is likely to be endangered based on its occurrence on a single small island and the paucity of collections; however, the island is not well-collected, so re-collection of this plant is a priority.

Discussion.

Solanum macrothyrsum is a rare liana endemic to Mayotte. It has large bright inflorescences of 15-50 white or violet flowers, large, membranous leaves on long petioles, a very small calyx (less than 1/8 of the corolla length at anthesis) and noticeably short, plump anthers (2.5-3 × 1.5-2 mm) on comparatively long filaments (1-1.5 mm). Solanum macrothyrsum is unusual in the group in having little pubescence on its vegetative parts, except some isolated trichomes on abaxial side of the midvein forming tufts in the vein axils (domatia) (see Fig. 15 ). The four duplicates of the type collection show considerable variation in leaf size, leaf thickness and venation; this perhaps represents leaves growing in the sun and in the shade or the type could have been gathered from several plants.

Since its original description by Dammer (1906), Solanum macrothyrsum been been known only from the type collection. It was rediscovered on the main island of Mayotte, Maore, in 2001 (Barthelat & Ali Sifari 559).

There are no species of Solanum on Mayotte similar to Solanum macrothyrsum . The species that most resembles Solanum macrothyrsum is Solanum ivohibe from eastern Madagascar: they share long petioles, decurrent leaf bases and branched inflorescences with a long peduncle. The two taxa are clearly distinct. Solanum macrothyrsum has anthers 2.5-3 mm (versus 3.5-4 mm) long, inflorescences branching 2-3 times (versus branching once), 15-50 (versus 10-16) flowers per inflorescence, peduncle 4.5-7 cm (versus 2-2.7 cm) long, and calyx lobes up to 0.5 mm long (versus 0.8-2 mm long). Solanum madagascariense is the only species with short anthers and open, lax inflorescences like Solanum macrothyrsum . Solanum macrothyrsum differs from Solanum madagascariense in its membranous (versus thick chartaceous to coriaceous) leaves, smaller leaf length to width ratio, petiole 1.5-4 cm (versus 0.4-2 cm) long, and smaller calyx, less than 1/8 (versus 1/6-1/3) of corolla length at anthesis.

Edmonds (2012), following the suggestion of R.N. Lester (pers. comm.) and Jaeger (1985) suggested that Solanum macrothyrsum was synonymous with Solanum benderianum (here treated as a synonym of Solanum runsoriense ) from Ethiopia, Uganda and Kenya. Bitter (1917) also placed Solanum macrothyrsum as a relative of the Solanum terminale alliance (his section Afrosolanum ) rather than with the Madagascar endemic species. There are numerous differences between these taxa: the calyx lobes of Solanum macrothyrsum are less than 0.5 mm long while the calyx lobes of Solanum benderianum are 2-4 mm long; the petioles of Solanum macrothyrsum are often longer than ½ of the leaf length while the petioles of Solanum runsoriense are less than 1/3 of the leaf length. In addition, the anthers of Solanum runsoriense have pores that elongate to lateral slits following dehiscence, while Solanum macrothyrsum , like the Malagasy members of this group, has anthers with distinct pores that never elongate. Solanum terminale also occurs in the Comoro Islands, but is known there from only a few collections (see discussion and specimens examined for Solanum terminale ). Solanum macrothyrsum differs from Solanum terminale in its anthers that never become longitudinally dehiscent, its more openly branched inflorescences with widely spaced flowers, and its tufts of trichomes in the axils of the main leaf veins on the abaxial surfaces.

Bitter (1917) cites duplicates of type collection from B and P. Dammer almost certainly worked from the B duplicate which is now destroyed. D’Arcy and Rakotozafy (1994) stated that the lectotype is held at P but do not mention which of the four duplicates they chose. Of these one marked in pen as lectotype, two marked as isolectotypes and one is not annotated with a type label. We have selected the duplicate (P00184304) annotated as “lectotype” (although it is not in D’Arcy’s handwriting) as the second stage lectotype for Solanum macrothyrsum . Edmonds (2014) was apparently unaware of this lectotypification when she designated as “lectotype” a Kew duplicate of Humblot 387; her lectotypification is superfluous, despite D’Arcy and Rakotozafy (1994) not having stated "designated here" and identifying a particular sheet.

Specimens examined.

Mayotte (French Overseas Department). Maore: Grande Terre, Tsararano, Reserve Forestiere de Tchaourembo , 20 Oct 2001, Barthelat & Ali Sifari 559 (G, K, MO, P) .

Figures

Figure 15. Solanum macrothyrsum Dammer. A Flowering branch B Open flower C Anther, showing round, clearly delineated pores D Simple trichome E Dendritic trichome. (based on: A-E Barthelat et al. 559). Scale bar: A = 2.5 cm; B = 7 mm; C = 3.3 mm; D, E = 0.3 mm. Drawn by Lucy T. Smith.

Figure 16. Distribution of Solanum macrothyrsum Dammer.