Plants usually growing in water. Leaves sheathing at the base, often floating on water. Flowers green, bisexual or unisexual. Perianths 3-4 lobed or 0. Stamens hypogynous. Ovary of 1-4 carpels. Style I. One seed in each carpel.

Potamogeton L. Pond-Weed

Leaves floating and opaque or submerged and translucent, stipulate or not. Perianth-segments 4, small, green. Stamens 4.

A rather large genus spread almost all over the globe; but with only one or two representatives in the high Alps.

Potamogeton Filiformis Persoon

Stem branching from the base. Leaves linear-filiform, 1-nerved. Spikes on long stalks. Fruit globular, with very short beak.

Alpine lakes, and rarely lower. It is abundant at the shallower end of the Lake of Mont Cenis (6300 feet) and in several Alpine lakes in Switzerland. It flowers in July; rare.

Distribution

S. Tyrol, Switzerland, Western Alps, Central and Northern Europe. British.

Potamogeton Alpinus Balbis (P. Rufescens Schrad)

Stem simple, cylindrical; submerged leaves narrow-lanceolate, sub-obtuse, translucent; floating-leaves, when they exist, coriaceous, oblong-spathulate, reddish. Stipules large. Fruiting-spike 2-4 cm. long, cylindrical, compact, on longish peduncles. Carpel compressed, keeled at the back, with distinct beak.

Stagnant or slowly running water, especially in the mountains.

Distribution

Europe, N. and N.W. Asia, N. America. British.

Many of the British species of Potamogeton are found in Switzerland, but chiefly in the plains.