Morphological and molecular characterization of Chnoospora minima (Scytosiphonaceae, Ectocarpales) along Mexican coasts, with the description of C. ramosissima sp. nov.

Chnoospora is one of the genera in Scytosiphonaceae with many taxonomic changes, comprising only two currently taxonomically accepted species. Chnoospora minima, its type species, has the widest distribution range and is characterized by a simple morphology with cylindrical or flattened thalli and dichotomous branching. On the Mexican coasts, its distribution is disjunct, being recorded on both the Pacific and Atlantic sides. In the present study we aim to characterize morphologically and molecularly the Mexican populations of C. minima. Our results revealed two phylogenetically independent groups, corresponding with different species with sympatric distribution in the tropical Mexican Pacific, C. minima and C. ramosissima sp. nov. Chnoospora ramosissima has the typical morphology of the genus, however, it is distinct in having relatively constant length of the branching segments, that are gradually reducing towards the apical portions, giving the thallus a profusely branched appearance; in addition, cellular measurements also differ between them. In contrast, C. minima, presented five different morphotypes on the Mexican coasts, however, all of them were different from C. ramosissima by having a central branching segment longer than the rest, subsequently reducing towards the apical portions, giving the thallus the appearance of being elongated and little branched.