An updated classification of growth forms in non-geniculate coralline algae (Corallinophycidae, Rhodophyta)

The current challenge of defining growth forms in the non-geniculate coralline red algae was addressed. Since the 19th century, those who have worked on this large and globally distributed group of algae have tried to summarize and systematically describe their growth forms. This effort resulted in a plethora of terms, which could sometimes be confusing, overlapping, and difficult to apply in the field. We reviewed the past literature to provide a coherent key to the non-geniculate coralline growth forms, incorporating the latest observations. Our revision expands the 10 currently recognized growth forms (unconsolidated, encrusting, warty, lumpy, fruticose, discoid, layered, foliose, ribbon-like, and arborescent) by redefining some of them, by reintroducing the columnar growth form, and by adding two new growth forms—convoluted and imbricate—to include recently documented specimens. This updated and refined tool better encompasses the diverse external morphologies of non-geniculate corallines. The goal was to facilitate taxonomic descriptions and to support ecological studies of non-geniculate corallines given the extreme difficulty of identifying species using only external characters.