A taxonomic study on two Japanese species of Gracilaria: Gracilaria shimodensis sp. nov. and Gracilaria blodgettii (Gracilariales, Rhodophyta)

Abstract

SUMMARY Japanese populations of the red alga Gracilaria blodgettii Harvey (Gracilariaceae, Gracilariales) were reinvesti-gated by morphological and cultural studies. Plants of populations growing on the Pacific coast of central Japan (Shizuoka and Chiba Prefectures) produce deep pot-shaped, Verrucosa-type spermatangial conceptacles and are entirely different from genuine G. blodgettii from the Caribbean Sea that bears shallowly depressed Textorii-type spermatangial conceptacles. However, plants from a population in southern Japan (Okinawa Prefecture) agree well with the circumscription of G. blodgettii, including the Textorii-type spermatangial conceptacles. The alga that produces the deep pot-shaped, Verrucosa-type spermatangial conceptacles and is distributed on the Pacific coast of central Japan is distinguished from all known species of Gracilaria by the following set of features in addition to the spermatangial feature and is described as Gracilaria shimodensis Terada et Yamamoto, sp. nov.: (i) remarkable constrictions at the bases of branches and branchlets; (ii) large gonimoblast cells; (iii) abundant traversing filaments; and (iv) a thick pericarp which consists of 8–10 layers of cells.