Exploring the Udoteaceae diversity (Bryopsidales, Chlorophyta) in the Caribbean region based on molecular and morphological data

[Display omitted] •A species delimitation approach combining distance and tree-based methods is proposed.•High congruence is reached between methods and chloroplast markers.•A morphology-based clustering method proved relevant for discriminating the morphospecies in the genus Udotea.•Udotea, Penicillus and Rhipocephalus revealed polyphyletic in our multilocus phylogeny.•The genus Udotea sensu stricto is redefined based on congruent genetic and morphological data. The Udoteaceae family (Bryopsidales, Chlorophyta) is known to be highly diverse morphologically in the Caribbean region, but only few studies have studied its genetic diversity. Using an integrative taxonomic approach, this study aimed at (1) exploring the Udoteaceae species diversity using a combination of five DNA-based species delimitation methods and morpho-anatomical data for confirmation; (2) estimating the discriminatory power of traditional diagnostic characters using a morphology-based clustering method and statistical analyses focused on the genus Udotea; and (3) reconstructing the phylogeny of the family based on a multilocus analysis (tufA, rbcL, 18S rDNA). Our results revealed strong congruence between species hypotheses across delimitation methods and markers. Morpho-anatomical characters proved essential to validate these hypotheses, to assign species names and to unveil new species. Morphological analyses led to relevant results for accurately discriminating Udotea morphospecies. Siphon features and cortication were key characters to define supra-specific groups and to revise the taxonomy of the genus Udotea. Phylogenetic analyses confirmed the polyphyly of Udotea, Rhipocephalus and Penicillus, which led us to propose a revised definition of Udotea sensu stricto based on both genetic and morphological data. Finally, our study emphasizes the importance of combining genetic and morphological data for the taxonomic revision of the Udoteaceae, but stresses the need of including more taxa from other geographical regions to better resolve taxonomic issues.