New genus Koliellopsis (Trebouxiophyceae, Chlorophyta):: its phylogenetic position inferred from ultrastructure and nuclear ribosomal DNA sequences

Koliellopsis inundata Lokhorst gen. & sp. nov. (Trebouxiophyceae) is described from periodically flooded agricultural fields in the borderland of Belgium and the Netherlands. This new, unbranched, filamentous alga is typified by relatively long vegetative cells, which have a bilobed, laminate chloroplast with a nucleus positioned in its median constriction. Its filaments lack a distinct basal-distal differentiation and both ends terminate in about equally shaped, rounded or, more often (slightly) tapering cells. Despite its semiterrestrial occurrence the new alga does not attach to hard substrate, presumably owing to the lack of end cells to produce mucilage and to function as a holdfast. The systematic position of Koliellopsis among the green algae is inferred from ultrastructural examinations of the cell division patterns and from phylogenetic analyses of partial 18S rRNA gene sequences.