CONCORDANCE OF MOLECULAR AND ULTRASTRUCTURAL DATA IN THE STUDY OF ZOOSPORIC CHLOROCOCCALEAN GREEN ALGAE1

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Abstract
Alternative evolutionary hypotheses generated from features of vegetative cell morphology and motile cell ultra‐structure were investigated using a molecular data set. Complete nuclear‐encoded small subunit (18S) ribosomal RNA (rRNA) gene sequences were determined for six species (three each) of the chlorococcalean green algae “Neo chloris” andCharacium. Based on motile cell ultra‐structure, it was previously shown that both genera could be separated into three distinct groups possibly representing three separate orders and two classes of green algae. 18S rRNA gene sequences were also obtained for three additional taxa,Dunaliella parvaLerche,Pediastrum duplexMeyen, andFriedmannia israelensisChantanachat and Bold. These organisms were selected because each, in turn, is a representative of one of the three ultrastructural groups into which theNeochlorisandCharaciumspecies are separable. Phylogenetic analyses utilizing the molecular data fully support the ultrastructural findings, suggesting that the similar vegetative cell morphologies observed in these organisms have resulted from convergence.