The Klebsormidiales is a small and poorly known group of charophyte algae. Members of this order grow as unbranched filaments, typically with a single pyrenoid for storage of starch reserves, and and one or two chloroplasts against the inner side of each cell.
There are only three genera in the order, comprising approximately 40 species. The genera Klebsormidium and Stichococcus are most frequently found growing in soil and on other moist substrates, but sometimes they may also be found growing in aquatic habitats. Raphidonema, the third genus of the order, is known primarily from montane snow fields at high elevation.
Unlike other charophytes, cell division in the Klebsormidiales occurs through formation of a cleavage furrow, but apparently neither a phragmoplast nor a cell plate is formed. Still, in many ways cytokinesis is similar to that in the Zygnematales, and for this reason a close relationship between the two orders has been suggested. The presence of a phragmoplast is the standard method of cell division both in the charophytes and in the plants, and the lack of this feature is one reason that the Klebsormidiales has only recently been reclassified into the Charophyceae.
Reproduction in the order occurs primarily by asexual fragmentation, in which the filament fractures into pieces, each of which develops into a new filament. Sexuality has not been documented in the members of the group.
Unlike the other two genera, Klebsomidium has been known to produce biflagellated zoospores. These motile spores swim away, eventually settling to develop into a new filament. The spores are covered with small square scales similar to those in certain chlorophyte green algae, but also possess features characteristic of land plants. The two flagella are inserted asymmetrically, and lie over a multilayered structure (MLS).
The Klebsormidiales have no fossil record.
Photo of Klebsormidium courtesy Richard M. McCourt, from the PSA slide collection.