Molecular evaluation of the validity of the morphological characters of three Swedish Chara sections: Chara, Grovesia, and Desvauxia (Charales, Charophyceae)

Charophytes are aquatic macrophytes with a complex morphology that belong to the Streptophytina phylum. The high degree of morphological plasticity in the genus Chara has led researchers to propose two competing species concepts, a micro- and macrospecies concept, the relevance of which we tested by phylogenetic analyses. We conducted a phylogenetic survey based on the phylogenetic relationships between 14 species of the genus Chara using molecular data from two nuclear (18S rDNA, nrITS-1) and three chloroplast (rbcL, atpB, matK) markers. As the combined molecular data indicated that the overall level of genetic divergence between the investigated species was, at <= 3%, relatively low, a robust species delineation was difficult to achieve. The sequence dataset of 6214 base-pairs did not separate individuals of closely related taxa with distinct morphological characters; e.g., the interspecific genetic variability for C. contraria and C filiformis or C. rudis and C. hispida was zero. In contrast, the molecular data revealed clear differences between C. vulgaris and C. contraria; species that are distinguished only by their relative levels of development of primary and secondary cortex cell rows. The low levels of genetic variability between as well as within the taxa studied here suggest that there has been a relatively recent, but still incomplete, speciation of Chara species. (C) 2016 Elsevier B.V. All rights reserved.