Taxonomic Studies in the Genus Disphyma N. E. Br

Abstract

A taxonomic study of the genus Disphyma N.E.Br. has been made with particular emphasis on the validity of the generic characters and the position of D. australe (Ait.) J.M. Black within the genus. Disphyma australe was also found to be the type species of the genus and not D. crassifolium as has been generally accepted. It was also found that no holotype or lectotype of D. australe exists. D. australe is shown to comprise three taxa, one in Australia, and two in New Zealand. One N.Z. taxon is abundant on all the N.Z. Islands except the Chathams, and the other is restricted to the Chatham Islands. The former species, D. australe in the emended sense, is shown to lack all the characters of the genus of which it is the designated type. This problem is discussed; and it is considered that D. australe should be rejected as the type species as it is contrary to the protologue description of the genus. Another element studied by Brown must be selected as the type species. Capsule structures are studied in detail and the generic characters, as understood by Brown, are considered too narrow if one continues to include D. australe (emended) in the genus. The author considers that the generic limits should be expanded to include this species and that the genus be divided into two sub-genera. Seed of all the species of Disphyma were examined and a comparison of ultra-structures of the seed testa in two species is given.