Morphology and phylogeny of parasitic and free-living members of the genus Phyllosiphon (Trebouxiophyceae, Chlorophyta)

The trebouxiophycean genus Phyllosiphon occurs as an endophytic leaf parasite of the Araceae. However, sequences similar to those acquired from siphonous parasitic thalli were also recently identified in various subaerial biofilms. In this study, we confirmed that free-living Phyllosiphon populations occur in corticolous biofilms as chlorelloid unicells with morphological features typical of the Watanabea clade. These free-living unicellular Phyllosiphon populations asexually reproduce by autospores and are culturable outside of the host plants. While the majority of the 18S rDNA sequences from the parasitic thalli were the same as those in previously published research, the free-living populations from the biofilms probably represented several different species of the Phyllosiphon clade. Phylogenetic analyses using the rbcL gene sequences confirmed the position of the genus Phyllosiphon within the Watanabea clade, but distinct from the clade of the genera Chloroidium and Parachloroidium typified by a single codon insertion at position 286 of the gene.