An order of freshwater algae possessing unbranched filaments. Sexual reproduction takes place via conjugation.

A phylum of photosynthetic EUKARYOTA bearing double membrane-bound plastids containing chlorophyll a and b. They comprise the classical green algae, and represent over 7000 species that live in a variety of primarily aquatic habitats. Only about ten percent are marine species, most live in freshwater.

The relationships of groups of organisms as reflected by their genetic makeup.