Phylogeny of Trachelomonas and Strombomonas (Euglenaceae) Based on Morphological and Molecular Data

The classification of Trachelomonas and Strombomonas is based on the morphology of loricae, which may not reflect phylogenetic relationships. There are different views on the relationship between the two genera. It is thus important for researchers to classify the two genera based on more characteristics besides loricae, such as protoplast and molecular data, and to establish a natural classification system. In this study, 29 strains (13 species) of Trachelomonas and 12 strains (eight species) of Strombomonas were collected from various locations in China. The morphological characteristics of Trachelomonas and Strombomonas were observed in the field and culture conditions, and the sequences of nuclear SSU rDNA, nuclear LSU rDNA, plastid-encoded LSU rDNA and plastid-encoded LSU rDNA of strains were obtained. We constructed a phylogenetic tree by combining four gene sequences with maximum likelihood and Bayesian methods. Based on the development of the loricae, it was found that the shape of the loricae and the presence or absence of the collar were relatively stable in culture, while the length of the collar presence or absence of spines and the color of the loricae changed. The phylogenetic tree showed that Trachelomonas and Strombomonas were sister branches, which supported Trachelomonas and Strombomonas as independent genera. Taxa in the genus Strombomonas sorted into two clades and Trachelomonas sorted into five strongly supported clades. Key morphological features could be attributed to each of the clades.