Potamogeton pusillus L.

pusillus: insignificant, small, weak

Submerged herb, with stems up to 1 m. Rhizome 0 or poorly developed. Stipular sheaths 6-17 mm, tubular, splitting later. Leaves c.20-40 × 1-2 mm, linear, all submerged, firm and translucent; apex obtuse, with 2 lateral longitudinal veins joining the midrib abruptly near the tip at unequal heights. Lacunar system 0 or sometimes a very narrow dense band flanking the midrib. Spikes usually shorter than leaves; flowers 2-4 per whorl with up to 4 whorls per spike. Drupe 2-2.5 mm, obovoid, smooth; beak short and straight.

Widespread in Africa, Europe, temperate Asia and North America. Less common in tropical America and Asia.