Potamogeton praelongus

Potamogeton praelongus, commonly known as whitestem pondweed in North America and Long-stalked Pondweed in Britain, is a large, perennial aquatic plant in the family Potamogetonaceae. It is widely distributed in lakes and rivers in the northern hemisphere, but is sensitive to poor water quality. Potamogeton praelongus has a Holarctic distribution, occurring in northern Europe (Britain, Ireland, Iceland, Scandinavia, Germany, Switzerland, France, Poland, Russia, the Baltic States), Greenland, Asia (Siberia, China, Korea, Japan), North America (northern USA, Canada). There are outlying populations in the Caucasus, Pyrenees and western USA. Ecological Requirements and Ecological Requirements. P. praelongus requires clear, deep water with at least some basic influence, and rarely grows in water less than 1 m deep. In Britain is usually found in lakes with limestone, marl or basalt geology, and it is absent from acidic lakes such as are common in Wales. It also occurs in slow-flowing rivers and disused canals. Long-stalked pondweed tends to be a rather rare plant within its range; for example, in a study of more than 3,500 British lakes, it occurred in only 88, most of which had low-moderate alkalinity and were dominated by isoetids. The seeds require a cold period to encourage germination.