Rhodophycean Pit Plugs: An Ultrastructural Survey With Taxonomic Implications

Abstract

The fine structure of pit plugs was examined in 63 species of red algae representing 34 families. The number of plug cap layers was found to be a taxonomically reliable character when tested against a recent revision of the Rhodymeniales which established the order Palmariales. In a broader survey involving all the orders of red algae possessing pit plugs, three basic plug cap configurations were detected. These differ in having one, two, or no plug cap layers. Some taxa have plug caps in which the outer cap layer is greatly elaborated, however, this layer was shown to be positionally and cytochemically identical, thus probably homologous, to the outer cap layer of the typical two-layered plug cap. The pit plug character confirms the validity of the order Palmariales and indicates that the Nemaliales and Cryptonemiales are heterogeneous assemblages. Revision of these groups along lines indicated by the plug character is supported by significant features of morphology and reproduction. These correlations lead us to propose that Rhodophysema and Coriophyllum be transferred to the Palmariales, that the Gelidiales be resurrected, that the Bonnemaisoniales (including the Naccariaceae) is deserving of recognition, that the Batrachospermaceae be raised to a higher rank which will also receive the Lemaneaceae and the Thoreaceae, and that the Corallinaceae and Hildenbrandiaceae both be raised to ordinal status. The authors would like to thank

Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae

“…In rhodophytes, diffuse growth characterizes the early branching lineages, such as the bangiophytes, whereas filamentous florideophyceans have apical growth meristems [88]. The presence of a central pore in Rafatazmia septa and of small bodies in corresponding positions in other septa is reminiscent of the mode of septation in rhodophytes, in which new septa are commonly incomplete and the central pore may later be filled with a tubular membrane called a primary pit plug, connecting the two daughter cells; pit plugs are unique to multicellular red algae and are particularly common in the Bangiophycea/Florideophycea clade [92,100]. The preservation of the Rafatazmia structures in diagenetic apatite, however, does not allow any definitive comparison with rhodophyte pit plugs.…”

MOLECULAR SYSTEMATICS OF THE FLORIDEOPHYCEAE (RHODOPHYTA) USING NUCLEAR LARGE AND SMALL SUBUNIT rDNA SEQUENCE DATA

“…Our analyses of all data sets consistently recovered the same result with full bootstrap support. All members of this lineage are characterized by pit plugs with a single cap layer and a membrane (Pueschel and Cole 1982). The LSU sequence determined herein had a putative group I intron of 540 base pairs at position 844.…”

“…Within lineage 2, analyses of LSU‐only and LSU–SSU data did not provide increased support for previously unresolved nodes relative to published SSU phylogenies, although topologies and support were congruent in all cases (Saunders and Bailey 1997, Harper and Saunders 1998, Vis et al 1998, Sheath and Müller 1999, Choi et al 2000). For those species for which ultrastructural data are available, pit plugs in this lineage are characterized by having two cap layers (Pueschel and Cole 1982). A recent SSU investigation (Choi et al 2000) led to the proposal of a new order, Balliales, in lineage 2 for species previously classified in the Ceramiales (lineage 4).…”

Organization of plastid genomes in the freshwater red algal order Batrachospermales (Rhodophyta)

“…). Thoreales was originally included in Batrachospermales (Pueschel and Cole ), but was separated into its own order (Muller et al. ).…”

“…). It is presently characterized by the following combination of characters (Pueschel and Cole , Garbary and Gabrielson , Kumano , Entwisle et al. ): (i) thalli heterotrichous, uniaxial, gelatinous, or cartilaginous; (ii) axial cells bearing determinant lateral assimilatory filaments; (iii) pit plugs with two cap layers, with an expanded dome‐shaped outer layer; tetraspores lacking, meiosis in diploid vegetative cells giving rise to haploid axes; (iv) multiple discoid chloroplasts lacking pyrenoids; (v) exclusively freshwater distribution.…”