M. spicatum: aquatic; stems immersed, ascending to the surface, more or less branched; leaves whorled along the whole length of the stem, the numerous capillary segments entire; flower-spike terminal, slender, 2-3 inches long, protruding from the water, bearing minute flowers arranged in little whorls, the upper flowers usually males, and the lower ones females; bracts small, entire. - Ditches and ponds. Fl. July, August.

M. verticillatum: aquatic; like the last, but the flowers in the axils of the upper leaves, immersed, and rarely forming a spike protruding above the water; bracts or floral leaves longer than the flowers, and pinnate like the stem-leaves. - Ditches and ponds. Fl. July.

(104) Hippuris. Marestail. H. vulgaris: aquatic; stems erect, simple, the upper part projecting 8-10 inches out of the water, crowded by whorls of 8-12 linear entire leaves, the submerged ones more elongated and flaccid; flowers minute, sessile in the axils of the upper leaves, consisting of a minute ovary, crowned by a scarcely perceptible border representing a calyx, and bearing a single small stamen, and a short thread-like style. - Shallow ponds and ditches. Fl. June, July.