Leptophytum (Corallinaceae, Rhodophyta): To be or not to be?—That is the question, but what is the answer?

Abstract

The question of whether or not Leptophytum (Corallinaceae, Rhodophyta) should be recognised as a distinct genus has been addressed using new data generated from type and other specimens combined with analyses of previously published data from various authors. The results have shown that none of the criteria proposed to separate Leptophytum from Phymatolithon are reliable at generic level. Some lead to the exclusion of type species from genera, others are impossible to assess because information is lacking for virtually all included species, others have character states that intergrade and thus are unsuitable and still others appear to be useful for separating species but not genera. Most of the character states proposed as diagnostic of Leptophytum are unknown or are not present in most of the species that were explicitly included in the recent proposed re-instatement of the genus and, in some cases, species included in Leptophytum show the opposing character state for Phymatolithon. No serious conflict occurs between the holotype fragments of Leptophytum laeve (the type species of Leptophytum) and the designated epitype and the designation of an epitype is fully justified because all of the characters evident in the holotype are demonstrably ambiguous and could apply to more than one species. Moreover, new evidence supports the probable conspecificity of the holotype and the designated epitype and reinforces the conclusion that Leptophytum should not be recognised as a genus distinct from Phymatolithon. Nomenclaturally, the correct authorship of the name of the type species of Leptophytum is L. laeve Adey and not L. laeve (Strömfelt) Adey or L. laeve (Foslie in Rosenvinge) Adey, and for purposes of priority, the name Leptophytum laeve dates from 1966.