asemoidussa

Asemoidussa is a genus of green algae within the family Chlorellaceae. The genus was first described by botanist L. J. Nesbitt in 1938, based on specimens collected from freshwater streams in the alpine regions of the Southern Alps. Asemoidussa species are characterized by their filamentous thalli, which grow in dense mats on submerged stones and streambeds. Cell morphology features long, threadlike chains of small, oval cells with a single, parietal chloroplast. The cell walls are composed of cellulose and contain characteristic calcium carbonate deposits that give the filaments a slightly translucent appearance.

The genus includes three described species: Asemoidussa alba, A. brevicaulis, and A. crassicauda. A. alba is the most widespread, found in temperate freshwater systems across Europe and North America, while A. brevicaulis is restricted to high-altitude streams in the Himalayas. A. crassicauda, the most recently described species (2021), was identified from a survey of the Danube Delta, where it forms extensive biofilms on submerged litter. All species are generally considered non-pathogenic and play an ecological role in nutrient cycling, serving as a primary food source for microinvertebrates and contributing to the stabilization of stream substrates.

Taxonomically, Asemoidussa has been placed within the order Sphaeropleales based on analyses of 18S ribosomal RNA sequences. Phylogenetic studies suggest a close relationship with the genera Sphaerocystis and Chlorella. The genus is of interest to researchers studying freshwater algae adaptation to fluctuating oxygen levels, as some Asemoidussa species exhibit remarkable tolerance to hypoxic conditions, likely due to specialized respiration mechanisms. The algae's symbiotic associations with biofilms also make it a useful model organism for investigating microbial interaction networks in aquatic ecosystems.