Studies in the tribe Spermacoceae (Rubiaceae-Rubioideae): the circumscriptions of Amphiasma and Pentanopsis and the affinities of Phylohydrax

Abstract.

Phylogenetic analysis of rbcL cpDNA sequences for 34 members of the tribe Spermacoceae s. lat. indicates that the African genera Amphiasma, Conostomium, Manostachya, Pentanopsis and Phylohydrax form a strongly supported clade, characterised by basal placentation and heterostyly. This is a new position for the sea shore genus Phylohydrax that has previously been associated with Diodia and Spermacoce in Spermacoceae s. str. Amphiasma is not monophyletic as the two samples of A. gracilicaule included form a strongly supported clade with Pentanopsis fragrans. A new taxonomy is therefore proposed, where the previously monotypic Pentanopsis is circumscribed as a genus of two species in north-eastern tropical Africa, whereas Amphiasma is treated in its original sense as a genus of about eight species confined to south-central tropical Africa. The new combination Pentanopsis gracilicaulis is made.