CRYPTOMONAD EVOLUTION: NUCLEAR 18S rDNA PHYLOGENY VERSUS CELL MORPHOLOGY AND PIGMENTATION1

Abstract

A nuclear18S rDNA phylogeny for cryptomonad algae is presented, including 11 species yet to be investigated by molecular means. The phylogenetic positions of the cryptomonad generaCampylomonasandPlagioselmisare assessed for the first time.Campylomonasgroups most closely with morphologically similar species with the same accessory pigment from the genusCryptomonas. Plagioselmisgroups with the generaTeleaulaxandGeminigeraforming a clade whose members are united by unusual thylakoid arrangement. Nuclear 18S rDNA phylogeny divides cryptomonads into seven major lineages, two of which consist of the monospecific generaProteomonasandFalcomonas.Analysis of nuclear18S rDNA sequence supports suggestions that aFalcomonas‐like cryptomonad gave rise to all other blue‐green cryptomonads. New sequence from the plastid‐lacking cryptomonad genusGoniomonasis also included, and the order of divergence of the major cryptomonad lineages is discussed. The morphology, number, and pigmentation of the cryptomonad plastidial complex are congruent with nuclear 18S rDNA phylogenies. Host cell features, such as periplast type, furrow/gullet system, and cell shape, can be more variable and may be markedly different in species that are closely related by nuclear 18S rDNA phylogeny. Conversely, some species that are not closely related by molecular phylogeny may display a very similar, possibly primitive, periplast and furrow morphology.