NUCLEAR STAINING IN ALGAL HERBARIUM MATERIAL - A REAPPRAISAL OF THE HOLOTYPE OF CALLITHAMNION-DECOMPOSITUM AGARDH,J. (RHODOPHYTA)

The taxonomic importance of uninucleate vs. multinucleate vegetative c ells in the Ceramiaceae is emphasized. It has been possible to make vi sible nuclei in old material, including type specimens, using aceto-ca rmine and aceto-iron-haematoxylin stains. The holotypes of Ceramium ro seum and Callithamnion fasciculatum (currently known as Callithamnion roseum and Pleonosporium borreri var. fasciculatum) have uninucleate c ells and belong to Aglaothamnion. In contrast, the holotype of Callith amnion decompositum, a name that has been applied to collections of at least two uninucleate taxa, has multinucleate cells; its morphologica l and cytological details agree with those of specimens collected in F rance and Ireland that were previously thought to represent an undescr ibed species. Female reproductive morphology (described from a thallus with gametangia in addition to tetrasporangia), in conjunction with h abit and vegetative features, indicates that this species belongs to C ompsothamnion (Compsothamnieae), as a third species, being distinguish ed from C. thuyoides and C. gracillimum by its sessile, lateral tetras porangia. The required new combinations under Aglaothamnion and Compso thamnion are made.