Solanum macrothyrsum
Not known.
Solanum macrothrysum is 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). It apparently occurs in wet forests; 200 to 400 m elevation (calculated from locality information; elevation not recorded exactly on any specimens we have seen).
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.
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 x 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), S. 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 S. macrothyrsum. The species that most resembles S. macrothyrsum is S. 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 S. macrothyrsum. Solanum macrothyrsum differs from S. 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 S. macrothyrsum was synonymous with S. benderianum (here treated as a synonym of S. runsoriense) from Ethiopia, Uganda and Kenya. Bitter (1917) also placed S. macrothyrsum as a relative of the S. terminale alliance (his section Afrosolanum) rather than with the Madagascar endemic species. There are numerous differences between these taxa: the calyx lobes of S. macrothyrsum are less than 0.5 mm long while the calyx lobes of S. benderianum are 2-4 mm long; the petioles of S. macrothyrsum are often longer than ½ of the leaf length while the petioles of S. runsoriense are less than 1/3 of the leaf length. In addition, the anthers of S. runsoriense have pores that elongate to lateral slits following dehiscence, while S. 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 three collections (syntypes of S. comorense Dammer, Schmidt 263 and 284 [both presumably destroyed in Berlin] and a later gathering Humblot 1284, the neotype of S. comorense). There are no recent collections, and it is possible these represent mislabelling of collections from continental Africa. Solanum macrothyrsum differs from S. 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 S. 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.