THE PHYLOGENETICS OF ACROCHAETIALES REVISITED: INFERENCES FROM RBC L AND CHLOROPLAST ENCODED 23S R RNA SEQUENCE ANALYSIS

Abstract

Recent molecular evidence from 23S rRNA sequences has shed light on the phylogenetic status of Acrochaetiales and Palmariales, suggesting a paraphyletic Acrochaetiales and a monophyletic Palmariales‐Acrochaetiales assemblage characterized by the absence of both the carpogonial filament and associated post‐fertilization fusions. It has also brought into question the status of Palmariales. Despite these findings, the familial and generic systematics of Acrochaetiales have remained somewhat obscure, in large part due to inadequate taxon and gene sampling. In the present study we address this problem by performing phylogenetic analyses of rbcL and 23S r RNA sequences from acrochaetioid algae covering a broad range of morphologies. Our results confirm elements from several primarily chloroplast based classification schemes (Papenfuss 1945, 1947; Stegenga 1979, 1985; Lee & Lee 1988) while also providing new phylogenetics insight. Two groups are supported at the most inclusive level. Group I is marine, has parietal chloroplasts, and includes three clades delimited primarily by the presence/absence of pyrenoids, number of chloroplasts, and possibly spore germination pattern. Group II is more heterogeneous and consists of three clades differentiated largely by chloroplast type (stellate/parietal, pyrenoid present/absent) and number, habitat (marine/freshwater) and life history. Systematic criteria drawn from the closely related order Palmariales suggest that we recognize Group I as a new family, Colaconemataceae, and the three taxa in Group II as Acrochaetiaceae, Rhodochortonaceae and Audouinellaceae. Furthermore, each of the three groups in Colaconemataceae could be regarded at the generic level. We also report on the utility of 23S rRNA for red algal systematics.