A morphological and molecular assessment of the genus Prionitis J. Agardh (Halymeniaceae, Rhodophyta)

A critical reassessment of the morphological features of two closely related red algal genera, Grateloupia C. Agardh and Prionitis J. Agardh (Halymeniaceae), shows that members of the two genera share very similar reproductive (including the Grateloupia‐type auxiliary‐cell ampullae) and vegetative characters. Diagnostic features hitherto used for distinguishing these two genera, the texture of blades (lubricous to leathery in Grateloupia vs cartilaginous in Prionitis) and the position of reproductive structures (scattered over the entire blade in Grateloupia vs confined to particular portions of the blade in Prionitis), are continuous across some 75 species of both genera, thus making it difficult to draw a clear‐cut distinction between the two genera. In ribulose‐1,5‐bisphosphate carboxylase/oxygenase gene (rbcL) sequence analyses, the species of Grateloupia and Prionitis, including the two generitypes, constitute a large monophyletic clade in the Halymeniaceae. It is therefore proposed that Prionitis be included in the synonymy under Grateloupia and the appropriate combinations are proposed.