Solanum erythracanthum
Not known.
Madagascar, a common weed throughout; growing in disturbed vegetation and open forest; 0–1000 m elevation.
Solanum erythracanthum is a member of the spiny Madagascar clade within the Old World clade (Levin et al., 2006);within that group it belogns to a somewhat well-supported clade composed entirely of malagasy species and is sister to S. myoxotrichum (Vorontsova et al. 2013).
Bitter, G. 1923. Solana Africana. IV. Spec. Nov. Regni Veg. Beihefte 16: 1-320.
D’Arcy, W. G. 1992. Solanaceae of Madagascar: form and geography. Ann. Missouri Bot. Gard. 79: 29-45.
D’Arcy, W.G., & A. Rakotozafy 1994. Solanaceae. Famille 176, pp. 1-146. In Flore de Madagascar et des Comores, P. Morat (ed.). Muséum National D’Histoire Naturelle, Paris.
Dunal, M.F. 1852. Solanaceae.Pp. 1-690 in A. P. DeCandolle (ed.), Prodromus Systematis Naturalis Regni Vegetabilis 13(1). Victoris Masson, Paris, France.
Jaeger, P.-M. L. 1985. Systematic studies in the genus Solanum in Africa. PhD thesis. United Kingdom: University of Birmingham.
Levin, R.A., N.R. Myers, & L. Bohs 2006. Phylogenetic relationships among the "spiny" solanums (Solanum subgenus Leptostemonum). Amer. J. Bot. 93: 157-169.
Vorontsova, M. S., S. Stern, L. Bohs, and S. Knapp. 2013. African spiny Solanum (subgenus Leptostemonum, Solanaceae): a thorny phylogenetic tangle. Bot. J. Linn. Soc. 173: 176-193. doi:10.1111/boj.12053
Solanum erythracanthum is the most common of the Solanum species endemic to Madagascar and has been noted as “ecologically troublesome and highly resistant to human disturbance” (D’Arcy 1992). It displays remarkable phenotypic plasticity and encompasses a great range of variation, especially in leaf size and shape, with subentire to ornate lobing, sporadic occurrence of minor leaves, and color and shape of prickles. The most common morphotype (S. erythracanthum s.s. as described by Dunal 1852, and Bitter 1923) is a small-leaved weedy shrub with reddish young shoots, dense indumentum, frequently lobed leaves and up to 3 (rarely 4) flowers per inflorescence. The species concept adopted here is broadly similar to that used by D’Arcy and Rakotozafy (1994) and includes two morphotypes known from single collections and recognized as separate species by Jaeger (1985): S. nossibeense and S. flagelliferum. Solanum nossibeense appears to have small-leaved branches similar to S. erythracanthum and large-leaved branches with subentire leaves and numerous tetramerous flowers leading to placement in “section Torva” by Jaeger (close to S. tettense in the Giganteum group in the present system; both morphotypes are visible on one specimen in Perville 357 [P00349146]). Solanum flagelliferum was recognized on the basis of its entire acuminate leaves and long petioles. A considerable number of single aberrant collections are also known which could indicate undescribed species or fall within morphological variability within S. erythracanthum.
Solanum erythracanthum grows in dry to mesic environments and to some extent intergrades into the prickly large-leaved S. myoxotrichum from the wetter highland forests in northeastern Madagascar in terms of stem pubescence and leaf size. We accept these as separate species for convenience and because the number of intermediate collections in the above characters is comparatively small. Solanum erythracanthum can be distinguished from S. myoxotrichum by its indumentum on the main stems under 3 mm long (versus over 3 mm long in S. myoxotrichum), and calyx lobes 1.5-2.5 mm long in flower (versus 3-7 mm long in S. myoxotrichum). Solanum erythracanthum differs from S. batoides in its leaves over 2 cm long (versus under 2 cm long in S. batoides), at least some leaves growing on the main stems (versus all leaves on small short shoots in S. batoides) and main branches over 2.5 mm in diameter (versus under 3 mm in S. batoides).
Solanum erythracanthum was common in cultivation in Europe in the 19th century, and a large number of collections in European herbaria are possibly derived from a few early introductions.