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S. BERGER, U. FETTWEISS, S. GLEISSBERG, L.B. LIDDLE, U. RICHTER, H. SAWITZKY AND G.C. ZUCCARELLO. 2003. 18S rDNA phylogeny and evolution of cap development in Polyphysaceae (formerly Acetabulariaceae; Dasycladales, Chlorophyta). Phycologia 42: 506-561.
Cells of the members of the Dasycladales have a unique body plan well known from fossils. They persist today in 38 recognized species. This study investigates in detail the development of reproductive structures in 17 Polyphysaceae (= Acetabulariaceae) species and provides a molecular phylogenetic analysis of 18S ribosomal DNA sequence data of 23 species of the order Dasycladales, including 17 of the 19 extant members of the family Polyphysaceae. Reproductive cap development is documented by scanning electron microscopy in 17 species, by histological sections in five species, and by growth measurements. Other morphometric data are also provided for most species. Bayesian analysis of DNA data reveals three well-supported clades for which morphological synapomorphies exist, but which are not completely in accordance with previous generic concepts. An early-branching clade comprising the monotypic Chalmasia and two species of Halicoryne is characterized by the formation of buds by the pointed cap rays. The second clade, comprising five species of Polyphysa (except P. peniculus), is characterized by corrugation of the cell stalk. It forms a sister group to the third clade, which comprises all eight Acetabularia species, plus P. peniculus and Acicularia schenckii. This clade is united by the lack of a velum covering the developing caps and by the relative timing of cap ray initiation. The extended Acetabularia clade is also characterized by the presence of a corona inferior, a structure that apparently was secondarily reduced in P. peniculus. Acetabularia acetabulum, a model species for cell biology, is sister to all other species of this clade. Its unique, congenitally fused cap rays may have evolved by a simple shift of growth zones during cap initiation. We propose to include both the monotypic Acicularia (as Acetabularia schenckii) and Polyphysa peniculus (as Acetabularia peniculus) in the genus Acetabularia. For the remaining Polyphysa species of clade 2, a new genus name, Parvocaulis S. Berger et al., is proposed.
INTRODUCTION
The Dasycladales are an evolutionarily old green algal order dating from the Cambrian era. The fossil record shows that this group has flourished throughout several geological periods, producing a...