Desmidium

Desmidium is a genus of green algae, the type genus of the family Desmidiaceae. It has a cosmopolitan distribution in acidic, oligotrophic freshwater lakes and bogs. The genus name of Desmidium is derived from the Greek word 'desmos' (= ribbon, chain or bond). Desmidium consists of cells with two halves, called semicells; the cells are attached to each other at their ends, forming filaments. The cells can be longer or shorter than wide, with a median constriction (called an isthmus) where the two semicells join; the isthmus distinct or indistinct. Cells are oval or three- to five-angled in apical view; the apex of each cell is either flat or has a narrow process at each angle; cells are attached to each other by the entire apical surface or by the apical processes. The angles may be offset on each semicell, creating a helical pattern along the filament. Cell walls are smooth and covered with pores. Each semicell contains one stellate chloroplast; the chloroplast may have a single pyre......read more on Wikipedia.