Systematics of the marine microfilamentous green algaeUronema curvatumandUrospora microscopica(Chlorophyta)

Abstract

The microfilamentous green alga Uronema curvatum is widely distributed along the western and eastern coasts of the north Atlantic Ocean where it typically grows on crustose red algae and on haptera of kelps in subtidal habitats. The placement of this marine species in a genus of freshwater Chlorophyceae had been questioned. Molecular phylogenetic analysis of nuclearencoded small and large subunit rDNA sequences reveal that U. curvatum is closely related to the ulvophycean order Cladophorales, with which it shares a number of morphological features, including a siphonocladous level of organization and zoidangial development. The divergent phylogenetic position of U. curvatum, sister to the rest of the Cladophorales, along with a combination of distinctive morphological features, such as the absence of pyrenoids, the diminutive size of the unbranched filaments and the discoid holdfast, warrants the recognition of a separate genus, Okellya, within a new family of Cladophorales, Okellyaceae. The epiphytic Urospora microscopica from Norway, which has been allied with U. curvatum, is revealed as a member of the cladophoralean genus Chaetomorpha and is herein transferred to that genus as C. norvegica nom. nov.

Phylogeny and Molecular Evolution of the Green Algae

“…For example, strains conforming to the morphological circumscription of the genera Neochloris, Characium and Planophila have been found in all three classes (Watanabe & Floyd, 1989;Lewis et al, 1992;Watanabe et al, 2000;Friedl & O'Kelly, 2002). Similarly, species of the coccoid genus Chlorococcum and the filamentous genus Uronema were present in the Chlorophyceae as well as the Ulvophyceae (Watanabe et al, 2001;Krienitz et al, 2003;Leliaert et al, 2009a). Species of Chlorella were shown to be distributed between the Chlorophyceae and Trebouxiophyceae (Huss & Sogin, 1990;Huss et al, 1999;Luo et al, 2010).…”

“…Analyses of 18S datasets have supported the circumscription of traditional orders based on cytomorphological characteristics but could not resolve the relationships among them (Chappell et al, 1991;López-Bautista & Chapman, 2003;Watanabe & Nakayama, 2007;Leliaert et al, 2009a). Moreover, the monophyly of the class has been questioned because it lacks unique ultrastructural synapomorphies (Mattox & Stewart, 1984;O'Kelly & Floyd, 1984a).…”

“…The Cladophorales (including Siphonocladales) comprises four main lineages, likely from a filamentous marine ancestor (Bakker et al, 1994;Hanyuda et al, 2002;Leliaert et al, 2003;Leliaert et al, 2009a). The marine unbranched, microfilamentous Okellya forms the earliest diverging lineage, followed by the Aegagropila clade, which is often found in highly specialized freshwater habitats (e.g., lake-balls or epizoophytes on turtles and snails).…”

On the occurrence of Uronema marinum Womersley (Chaetophorales, Chlorophyta) in the north-western lagoons of the Adriatic Sea, Mediterranean Sea (Italy)

“…Its occurrence has been correlated with certain water column and surface sediment parameters and the presence of other common NIS that have also successfully colonized these environments. The new alien is rather similar in morphology to Okellya curvata (Printz) Leliaert & Rueness which occurs on the European Atlantic coast (Leliaert et al, 2009).…”

“…In the Pacific, Uronema marinum is reported throughout the year from shallow subtidal habitats of southern and western Australia, the South Great Barrier Reef, Micronesia and Hawaii (Womersley, 1984;Abbott & Huisman, 2004;Kraft, 2007). On the European Atlantic coast, between France and western Norway, a second species: Uronema curvatum Printz (Rueness, 1992;Maggs & O'Kelly, 2007) has been recognized recently as Okellya curvata (Printz) Leliaert & Rueness (Leliaert et al, 2009). It has a similar habit, but its vegetative cells lack pyrenoids.…”