A taxonomic revision of a Hypnea charoides-valentiae complex (Rhodophyta, Gigartinales) in Japan, with a description of Hypnea flexicaulis sp. nov.

SUMMARY Morphology of a Hypnea charoides-valentiae complex (Rhodophyta, Gigartinales) in Japan is investigated on the basis of field-collected and cultured plants. We can recognize two species, Hypnea charoides Lamouroux and H. flexicaulis Yamagishi et Masuda, sp. nov., which are distinguished by: (i) conspicuous percurrent main axes growing straight in the former versus less conspicuous percurrent main axes growing flexuosely in the latter; (ii) narrow branching angles (less than 90°) in the former versus wide branching angles (up to 150°) in the latter; (iii) the presence of branches and branchlets showing abrupt adaxial bending in the former versus those showing pronounced abaxial bending, some growing into hooked branchlets in the latter; and (iv) the absence (in the former) or presence (in the latter) of antler-like branches. Nucleotide sequences of the plastid-encoded large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase gene (rbcL) support the differentiation of these two entities: the pairwise distance between them was 83 b.p. (6.2%).