P1. Syst. Evol. 175:139-160 (1991) --Plant Systematics and Evolution © Springer-Verlag 1991 Printed in Austria The morphology, taxonomy and evolution of Rhodocoma (Restionaceae) H. P. LINDER and J. H. VLOK Received July 10, 1990; in revised version October 8, 1990 Key words: Angiosperms, Restionaceae, Rhodocoma. - Speciation, phylogeny, culm anat- omy, rhizome anatomy, morphology, taxonomy. - Flora of Africa. Abstract: The vegetative and reproductive morphology, culm and rhizome anatomy and seed surface micromorphology of Rhodocoma are described. It is shown that this variation is best contained by recognizing three new species in the genus. These new taxa are described, and the phylogeny of the genus is investigated by cladistic analysis. The environmental parameters and distributions of the species are related to the cladogram. This suggests that the species are at present ecologically separated, and indicates that the speciation may have been sympatric. This is the first support for the hypothesis that sympatric speciation may have been important in the speciose Cape flora. Rhodocoma NEES, a genus of six species, is a member of the Southern Hemisphere family Restionaceae. The genus is centred in the southern Cape Province, South Africa, where all six species occur between the coast and th~ Great Swartberg, some 90 km inland. Two of the species have a wider distribution, with outliers reaching Natal and the western Cape Province. Rhodocoma was separated from the polyphyletic Restio L., as circumscribed by PILLANS (1928), by LIEDER (1984), who showed that the species had many of the characters of Thamnochortus BERC. The pendulous male spikelets and erect female spikelets, the general growth-form and the appearance of the male flowers link the two genera. The culm anatomy also reveals similarities between the two genera. The general organization of the tissues in the culms is very alike in the two genera and in both curious gaps are found in the central ground tissue. However, Tham- nochortus is distinguished from Rhodocoma by the reduction in the ovary to a unilocular, indehiscent, but relatively soft-walled nutlet, and the possession of a single, plumose style. In addition, in the culm anatomy the epidermal cells have strongly thickened transverse walls which are wavy. This state has not been recorded from Rhodocoma. Rhodocoma, in turn, is defined by the single-flowered female spikelets and the structure of the seed-coat. On this basis, it was possible to delimit two monophyletic taxa, Rhodocoma and Thamnochortus, which are clearly very closely related by at least three synapomorphies. In the last review of the genus (LINDER 1985 b) three species were recognized: R. gigantea (KuNTH) LINDER, R. capensis NEES ex STEUD., and R.fruticosa (THuNB.) "