SPECIES OF ANTITHAMNION (RHODOPHYCEAE,CERAMIACEAE) OCCURRING ON THE SOUTHEAST AFRICAN COAST (NATAL)1

Three species of Antithamnion Naegeli were previously known from Natal, all reported since 1984. A more thorough collection of the flora in recent months has revealed that there are nine species in Natal, four of which are newly described. Vegetative characteristics are emphasized in this study of the taxonomy of Antithamnion, the most important being (1) size of axial cells, (2) form of whorl-branchlets, (3) size of whorl-branchlet basal cells, (4) size and shape of whorl-branchlet terminal cells, (5) size and position of gland cells, (6) primary or secondary derivation of indeterminate lateral branches, and (7) the relationship of primary indeterminate branches, if present, to normal arrangement of whorl-branchlets. Two closely related species, A. diminuatum Wollaston and A. eliseae sp. nov. have been grown in laboratory culture allowing for testing of stability and reliability of vegetative characteristics for use in taxonomic studies. Conclusions are that these criteria can be effectively used for these purposes. In addition to A. eliseae, A. nematocladellum, A. pterocladellum and A. adenocladellum also are described as new species. A tropical species previously known from the Caribbean and Red Seas, A. lherminieri Nasr, a species previously recorded from Japan, A. secundum Itono, a species previously known from California and Japan, A hubbsii Dawson, and two species from Australia, A. diminuatum Wollaston and A. divergens (J. Agardh) J. Agardh, are also described from Natal.