DIVERSITY AMONG TETRASPORALEAN TAXA: EVIDENCE FROM ULTRASTRUCTURE AND MOLECULES

Abstract

Recent phylogenetic studies of tetrasporalean exemplars using 18S rDNA revealed the extent of diversity among taxa in this non‐monophyletic group (Booton et al. 1998). In particular, two distinct tetrasporalean lineages were identified; one group allied with chlamydomonadalean taxa and the other group comprising taxa now placed in a separate order, the Chaetopeltidales. Using these observations as a framework, a new investigation of diversity among a broader sampling of putative tetrasporalean genera (e.g. Asterococcus, Chloranomala, Chlorophysema, Gloeocystis, Gloeodendron, Palmella, Paulschulzia, Physocytium, Schizochlamys and Tetraspora) was undertaken. Phylogenetic studies of both 18S and 26S rDNA were compared with ultrastructural investigations of vegetative cells. Molecular phylogenetic analyses corroborate the earlier 18S rDNA results, but also reveal additional diversity. The new data raise doubts regarding the monophyly of two genera, Palmella and Tetraspora. The new data also link two enigmatic green algal genera, Physocytium and Heterochlamydomonas, in a long‐branch lineage within the Chlamydomonadales. Another enigmatic genus, Schizochlamys, is allied with Bracteacoccus in the Sphaeropleales. Lastly, Chloranomala is resolved as an ally of Paulschulzia, Tetraspora sp., and the green flagellate, Lobomonas. Comparison of pyrenoid ultrastructure generally supports the molecular phylogenetic analyses, suggesting that this non‐molecular character will be a useful marker for broad phylogenetic studies of chlamydomonadalean taxa. (Supported by NSF grant, DEB 9726588)