Taxonomic Study of Pyrobotrys (Spondylomoraceae, Chlorophyceae) Based on Comparative Morphological and Molecular Analyses of Culture Strains Established Using Novel Methods

Abstract

Taxonomic studies of the spondylomoracean genus Pyrobotrys have remained at traditional levels due to the lack of molecular phylogenetic analyses and available culture strains for reexaminations. Here, we established new culture strains of Pyrobotrys using novel culturing methods, and classified them into three species, namely, P. casinoensis, P. elongata, and P. squarrosa, based on comparative microscopic observations and molecular phylogeny. Although P. elongata is characterized by its enormous stigma in cells of the most posterior tier in a colony, such a species has not been reported since its original description in 1938. In the present study, the presence of an enormous stigma was confirmed based on light microscopy in three P. elongata strains originating from two localities. Based on transmission electron microscopy, the large stigma of P. elongata was essentially identical to the stigma of other species of Pyrobotrys in having a single layer of stigma globules. Our molecular phylogeny demonstrated that P. elongata was robustly separated from other species of Pyrobotrys.