A guide to nongeniculate coralline red algal (Corallinales, Rhodophyta) rhodolith identification

Rhodoliths are free-living structures composed mostly of nongeniculate coralline red algae. Species that form rhodoliths usually cannot be identified with certainty using only growth form or other external morphological features. Accurate and reliable identification usually requires sectioning for examination of pertinent vegetative and reproductive characters. Simplified steps to facilitate identification of nongeniculate coralline red algal rhodoliths are presented in this paper. Identification is a twotiered process involving identification of specimens to genus followed by identification of specimens to species. We list the common nongeniculate rhodolith-forming genera (Hydrolithon, Neogoniolithon, Lithophyllum, Sporolithon, Lithothamnion, Phymatolithon, Mesophyllum and Spongites) and provide illustrations and/or references to important taxonomic characters useful for identifying specimens to genus level. We also provide references to recently published floristic descriptions or detailed taxonomic accounts to rhodolith-forming species in these eight genera to facilitate species identification.