A preliminary phylogeny of diatoms based on 28S ribosomal RNA sequence data

Abstract

A molecular phylogeny of the diatoms has been constructed from the nucleotide sequence of two domains of the nuclear-encoded large subunit ribosomal RNA in four centric and four pennate species. Distance and parsimony analyses support the monophyly of the diatoms and their closeness to the chrysophytes. The Centrales (radially symmetrical) appear to be paraphyletic: the centric Lithodesmium undulatum Ehrenberg (Lithodesmiales, Lithodesmiaceae) is associated with the pen-nate lineage. In the Pennales (bilaterally symmetrical), the araphids also appear to be paraphyletic. These phylogenetic inferences are in close congruence with those previously obtained from 18S rRNA data (Bhattacharya et al. 1992; Medlin et al. 1993). The evolutionary relationships of diatom families inferred from the ribosomal RNA data are discussed in relation to the fossil record.