Genetic and Morphological Diversity in the Green Algal Genus Caulerpa J.V.Lamouroux (Bryopsidales, Chlorophyta) in Thailand

Abstract

Caulerpa is a coenocytic green algal genus that is widely distributed in the intertidal and subtidal zones of tropical and subtropical seas. Some species show a complex external morphology. A high morphological plasticity and overlapping morphologies hamper the taxonomy of the genus tremendously. All previous taxonomic studies of Caulerpa in Thailand were based on morphological observations. Since then the taxonomic status of several Caulerpa species has been challenged by molecular studies. The present study aims to reassess the Caulerpa diversity in Thailand using morphological and molecular data (tufA gene and ITS rDNA sequences) from herbarium and fresh specimens. The result confirmed the occurrence of eight Caulerpa species in Thai waters, i.e., C. chemnitzia, C. lentillifera, C. macrodisca, C. racemosa, C. serrulata, C. sertularioides, C. taxifolia and C. verticillata. Specimens previously identified as C. corynephora in Thailand actually are a morphological variety of C. macrodisca. Then, there were three morphological groups of C. macrodisca, C. macrodisca ecad ashmeadii, C. macrodisca ecad corynephora and C. macrodisca ecad macrodisca. In addition, C. racemosa is represented by two distinct morphologies; C. racemosa ecad chemnitzia and C. racemosa ecad racemosa. It is concluded that Caulerpa species identification cannot rely on morphology alone. The tufA gene was useful for specific identification of Caulerpa, and ITS rDNA sequence was supported data. So, this study suggested that morphological and molecular data were good for Caulerpa diversity. In addition, several morphological Caulerpa species previously recorded for Thailand were not found during our field survey and their identity could not be confirmed with DNA sequence data obtained from herbarium specimens.