The Genus Sphinctospermum (Leguminosae): Taxonomy and Tribal Relationships as Inferred from a Cladistic Analysis of Traditional Data

Abstract

The systematic position of the monotypic genus Sphinctospermum has been confused, being placed in either of two tribes, Robinieae or Millettieae, of the Leguminosae subfam. Papilionoideae. Originally allied with Tephrosia (Millettieae), subsequent studies revealed that Sphinctospermum has a base chromosome number of x = 8 and seeds that accumulate the non-protein amino acid canavanine. Such evidence was used to support its inclusion in Robinieae. A cladistic analysis of primarily morphological data is presented that incorporates new or newly interpreted characters, including anatomical and developmental features. These data do not support a sister group relationship of Sphinctospermum and Coursetia, as previously proposed by some workers. Furthermore, the results of this analysis of traditional data are equivocal and suggest that the probable affinities of Sphinctospermum are just as likely to be with genera of Millettieae than with those of Robinieae.