Species and characteristics

Sometimes referred to as the "spiny solanums", this group is characterised by

• prickles on the stems and leaves of the majority of species
• stellate hairs on the majority of species
• long attenuate anthers with terminal pores (Leptostemon from lepto-, Gk for thin and stemon, Gk for stamen, is a reference to the stamens of this group)

While a few species may lack either prickles or stellate hairs they usually have at least one of these characteristics.

Subgenus Leptostemonum consists of up to 500 species world-wide, the majority occurring in Central and South America, Africa and Australia. The majority of Australian species, some 146 species, belong in this group.

Symon (1981) grouped the Australian species into 12 sections, the two largest, sect. Oliganthes and sect. Melongena, accounting for the majority of species.  

Whalen (1984) split the subgenus into 33 informal groups world-wide and these groupings were, for the main part, followed by Bean (2004), although some of Whalen's groups were subdivided. The groupings are narrower than those proposed by Symon e.g. Symon's Sect. Oliganthes accounts for Groups 25 and 27 of Whalen and the S. hystrix, S. ellipticum, S. macoorai, S. esuriale, S. lasiophyllum and S. echinatum groups of Bean. Symon's sect Melongena is equivalent to Whalen's Group 28 or the S. dioicum group  of Bean.

Lucid only supports 15 character states and so the groups of subg. Leptostemonum as elucidated by Bean (2004) could not all be included here. Introduced species such as S. wendlandii, S. giganteum, S. lasiocarpum, S. rostratum and S. sisymbrifolium and the native species S. pugiunculiferum are all single species members of groups of Leptostemonum not treated here.

Levin et al. (2006) undertook a world-wide phylogenetic analysis of the species of  subg. Leptostemonum. They found that the group was monophyletic, that many of the Whalen groups were supported and that the Australian species included in the study all belonged to a single Old World clade. The position of some of the introduced species in Australia such as the S. wendlandii group, included in subg. Leptostemonum by Whalen, was equivocal and some of the groupings of the Australian species will undoubtedly be the subject of further study.

Martine et al.'s (2006) phylogenetic study of the Australian species of sect. Melongena sensu Symon (1981), or Group 28 of Whalen or the S. dioicum group of Bean (2004), and composed of the andromonoecious and cryptically dioecious Solanum species, indicated that this group was not monophyletic and could be divided into 5 clades; two of these clades were composed of the cryptically dioecious species of Solanum and three of the andromonoecious species of Solanum.

This is clearly an area where there will be continuing change as the relationships of the species are clarified.

References:

Levin, R.A., Myers, N.R. & Bohs L. (2006). Phylogenetic relationships among the "spiny solanums" (Solanum subgenus Leptostemonum, Solanaceae). American J. Botany 93: 157-169.

Martine, C.T., Vanderpool, D. Anderson, G.J. and Les, D.H. (2006). Phylogenetic relationships of andromonoecious and dioecious Australian species of Solanum subgenus Leptostemonum section Melongena: Inferences from ITS sequence data. Systematic Botany 31: 410-420.