(Greek, marshy). Hydrocharitaceae. Aquatic herbs, one of which is grown in aquaria.

The genus is known in horticulture as including the ditch-moss, an interesting hardy perennial plant found in slow streams and ponds nearly throughout N. Amer., except the extreme north and particularly desirable for home and school aquaria. It is a slender, wholly submerged plant, with branching stems 4 in. to 3 ft. long, according to the depth of the water. The pistillate flowers are raised to the surface by their long calyx-tubes, and float there. The minute staminate flowers, which are rarely seen, commonly break off below, rise to the surface, float about, open, and shed their pollen. The fruit ripens below the surface, and the seeds rise. It reached England in 1841 and choked up many canals and waterways, notably the Cam. It was very abundant in 1852 and 1853, but declined in the next few years. Ducks, geese and swans are fond of it, and render great service in getting rid of it. It can be used for manure where it grows in sufficient quantities. Like many other water plants, it makes heavy buds in the fall (Fig. 1391), which drop to the bottom and grow in the spring.

This genus contains perhaps 10 species.

Canadensis

Mich. (Anacharis canadensis, Planch. A. Alsinastrum, Bab. Philotria canadensis, Brit.). Water-Weed. Ditch-Moss. Water-Thyme. Leaves in whorls of 3 or 4, or the lower ones opposite, linear, minutely toothed or not, 2-7 lines long, 1/2-2 lines wide: flowers white; calyx-tube of the pistillate flowers 2-12 in. long; spathes 5-7 lines long.

Winter bud of Elodea. (Nat. size)

Fig. 1391. Winter-bud of Elodea. (Nat. size)

Variety gigantea, Hort. Giant Water-Weed. A much stronger grower than the species and a desirable plant for the aquarium, and a good oxygenator. Now generally used in preference to the type.

Wm. Thicker and Wilhelm Miller.