Foliicolous algae are a common occurrence in tropical forests. They are referable to a few simple morphotypes (unicellular, sarcinoid-like or filamentous), which makes their morphology of limited usefulness for taxonomic studies and species diversity assessments. The relationship between algal community and their host phyllosphere was not clear. In order to obtain a more accurate assessment, we used single molecule real-time sequencing of the 18S rDNA gene to characterize the eukaryotic algal community in an area of South-western China. We annotated 2922 OTUs belonging to five classes, Ulvophyceae, Trebouxiophyceae, Chlorophyceae, Dinophyceae and Eustigmatophyceae. Novel clades formed by large numbers sequences of green algae were detected in the order Trentepohliales (Ulvophyceae) and the Watanabea clade (Trebouxiophyceae), suggesting that these foliicolous communities may be substantially more diverse than so far appreciated and require further research. Species in Trentepohliales, Watanabea clade and Apatococcus clade were detected as the core members in the phyllosphere community studied. Communities from different host trees and sampling sites were not significantly different in terms of OTUs composition. However, the communities of Musa and Ravenala differed from other host plants significantly at the genus level, since they were dominated by Trebouxiophycean epiphytes. The cryptic diversity of eukaryotic algae especially Chlorophytes in tropical phyllosphere is very high. The community structure at species-level has no significant relationship either with host phyllosphere or locations. The core algal community in tropical phyllopshere is consisted of members from Trentepohliales, Watanabea clade and Apatococcus clade. Our study provided a large amount of novel 18S rDNA sequences that will be useful to unravel the cryptic diversity of phyllosphere eukaryotic algae and for comparisons with similar future studies on this type of communities.

Background: The order Oedogoniales within the single family Oedogoniaceae comprised of three genera,Oedogonium,Oedocladium,andBulbochaetebased on traditional morphological criteria. While several molecular phylogenetic studies have suggested that bothOedogoniumandOedocladiummay not be monophyletic, broader taxon sampling and large amounts of molecular data acquisition could help to resolve the phylogeny and evolutionary problems of this order. This study determined five chloroplast (cp) genomes ofOedogoniumspecies and aimed to provide further information on cp genome for a better understanding of the phylogenetic and evolutionary relationships of the order Oedogoniales.Results: The fiveOedogoniumcp genomes showed typical quadripartite and circular structures, and were relatively conserved in their structure, gene synteny, and inverted repeats boundaries in general, except for small variation in genome sizes, AT contents, introns, and repeats. Phylogenetic analyses based on 54 cp protein-coding genes examined by maximum likelihood and Bayesian analyses using amino acid and nucleotide datasets indicated that bothOedocladiumandOedogoniumare polyphyletic groups. A positively selected gene (psbA) was identified in the twoOedocladiumspecies and the terrestrialOedogoniumspecies, indicating that terrestrial Oedogoniales taxa may have undergone adaptive evolution to adjust to the difference in light intensity between aquatic and terrestrial habitats.Conclusions: Our results enrich the data on cp genomes of the genusOedogonium. The availability of these cp genomes can help in understanding the cp genome characteristics and resolve phylogenetic and evolutionary relationships of the order Oedogoniales.

The order Trentepohliales is composed of a complex of five aerial genera of branched filamentous green algae, Trentepohlia, Printzina, Phycopeltis, Cephaleuros and Stomatochroon; polyphyly has been discovered in some of these genera and species. To clarify the diversity and some taxonomic problems in the Trentepohliales, we collected specimens from southern China and successfully cultured the majority of them. We carefully observed morphological traits and performed phylogenetic analyses based on new 18S and ITS rDNA sequences obtained during the present study. Our results suggested that the ostiole position of the zoosporangia might effectively indicate the main lineages of Trentepohliales, with reassessment of the genera Trentepohlia and Printzina required based on this ostiole positioning. However, further molecular investigation, particularly for the genus Phycopeltis, is required. Phenotypic plasticity was very common in Trentepohlia and Cephaleuros and the traditionally circumscribed taxa may not be reliable. In Cephaleuros, the lichenized species do not form a single clade and most species are paraphyletic. Additionally, we suggest that a lack of description of the internal systems could be one reason for the difficulties in species identification. Further taxonomic studies should focus on an emendation of Cephaleuros and elucidating the molecular diversity of Phycopeltis.