The genus Phymatolithon (Hapalidiaceae, Corallinales, Rhodophyta) in South Africa, including species previously ascribed to Leptophytum

•Leptophytum and Phymatolithon are the most contentious coralline algal genera.•SA taxa have not been formally transferred to Phymatolithon or reduced to synonymy.•Detailed accounts of taxa ascribed to the genus Leptophytum are presented.•We show characters upon which Leptophytum is based are unreliable for delimitation.•A key to the southern African species of Phymatolithon is provided.

Of the genera within the coralline algal subfamily Melobesioideae, the genera Leptophytum Adey and Phymatolithon Foslie have probably been the most contentious in recent years. In recent publications, the name Leptophytum was used in quotation marks because South African taxa ascribed to this genus had not been formally transferred to another genus or reduced to synonymy. The status and generic disposition of those species (L. acervatum, L. ferox, L. foveatum) have remained unresolved ever since Düwel and Wegeberg (1996) determined from a study of relevant types and other specimens that Leptophytum Adey was a heterotypic synonym of Phymatolithon Foslie. Based on our study of numerous recently collected specimens and of published data on the relevant types, we have concluded that each of the above species previously ascribed to Leptophytum represents a distinct species of Phymatolithon, and that four species (incl. P. repandum) of Phymatolithon are currently known to occur in South Africa.Here we present detailed illustrated accounts of each of the four species, including: new data on male and female/carposporangial conceptacles; ecological and morphological/anatomical comparisons; and a review of the information on the various features used previously to separate Leptophytum and Phymatolithon. Southern African species ascribed to the genus Phymatolithon may be separated from one another in the field by their growth forms, the substrata on which they are generally found, and the colour of living thalli. A key for identifying southern African specimens in the field is included. Our data support the conclusion that the characters upon which Leptophytum is based are unreliable for generic delimitation from Phymatolithon.