Recognition of Pachyarthron and Bossiella as distinct genera in the Corallinaceae, subfamily Corallinoideae (Corallinales, Rhodophyta)

New evidence supports recognition of both Pachyarthron and Bossiella as distinct genera within the Corallinaceae, subfamily Corallinoideae (Corallinales, Rhodophyta). Pachyarthron cretacewn, the type species of Pachyarthron, is confirmed to occur in Australia, and a new study of the designated lectotype of P. cretacea and of plants from Australia, Japan, Canada (British Columbia) and the United States (Alaska, Washington State) has shown that male conceptacles are produced both axially at branch tips and laterally on intergenicula. By contrast, only lateral conceptacles occur in Bossiella. Differences between Pachyarythron and Serraticardia & Marginisporum, the only genera of Corallinoideae known to produce both axial and lateral conceptacles, are outlined, and a comparison of and key to all genera of Corallinoideae are included. An emended generic description of Pachyarthron and an account of P. cretatceum are provided. Brief accounts of four infraspecific taxa never transferred into Pachyarthron but attributed to the homotypic synonym Amphiroa cretacewn also are included. These are Amphiroa cretacea f. breviarticulata (Areschoug) Yendo from the Caribbean; A. cretacea f. capensis (Areschoug) Yendo from South Africa; A. cretacea f. rosariformis Yendo from Japan; and A cretacea f. tasmanica (Sonder) Yendo from Australia. The biogeographic implications for Pachyarthron and Bossiella are reviewed; Bossiella Should be removed from the floras of Japan, Korea and China, whereas Pachyarthron should be added.