Taxonomic reassessment of rhodolith-forming species of Lithophyllum (Corallinales, Rhodophyta) in the Gulf of California, Mexico

Abstract

Rhodolith beds (beds composed of unattached coralline red algae) in the Gulf of California, Mexico, are widespread and commonly dominated by specimens belonging to Lithophyllum. The number of rhodolith-forming species of Lithophyllum in these beds, however, has been uncertain, and there are contradictory statements in the recent literature concerning putative species. Five species have been recognized, but it also has been suggested that these represent only a single polymorphic species. More than 700 specimens from 45 localities were examined and compared with all relevant types to determine how many species are represented and how they might be distinguished. Most of the types analyzed agree with the modern concept of Lithophyllum; however, two species, Lithophyllum californiense Heydrich and Lithophyllum bracchiatum (Heydrich) Me.Lemoine, do not agree with the modern concept of Lithophyllum and have been excluded from the genus. None of the characters used previously to delimit species in the group was taxonomically reliable. Moreover, an evaluation of all specimens based on modern characters, especially relating to tetrasporangial conceptacle anatomy, showed that only a single species was present, namely Lithophyllum margaritae (Hariot) Heydrich. Both within and between populations, L. margaritae exhibits a continuum of growth forms: encrusting to foliose to fruticose to warty to lumpy. The dominance of particular growth forms within an area appears to be linked to local environmental conditions.