Aquatic herbs, with simple erect stems, and verticillate simple entire leaves. Flowers small, axillary, perfect, or sometimes neutral or pistillate only. Limb of the calyx minute, entire. Petals none. Stamen 1, inserted on the margin of the calyx. Style filiform, stig-matic its whole length, lying in a groove of the anther. Fruit a small 1-celled 1-seeded drupe. [Greek, mare's-tail.]

Three known species, natives of the north temperate and arctic zone and of southern South America. Besides the 2 following, the third occurs in northwestern arctic America. Type species: Hippuris vulgaris L.

Leaves linear or lanceolate, in verticils of 5-12. 1. H. vulgaris. Leaves obovate, oblong, or oblanceolate, in verticils of 4-6.

2. H. tetraphylla.

1. Hippuris Vulgaris L. Bottle Brush. Mare's-Tail. Joint-Weed

Fig. 3077

Hippuris vulgaris L. Sp. Pl. 4. 1753.

Stem slender, glabrous, 8'-2o' high. Leaves linear or lanceolate, acute, sessile, 1/2"-12" long, 1"-2" wide, in crowded verticils of 6-12, more or less sphacelate at the apex; stamens with a short thick filament, and comparatively large 2-celled anther, dehiscent by lateral slits; seeds ovoid, hollow; stigma persistent.

Swamps and bogs, Labrador and Greenland to Alaska, south to Maine, New York, Illinois, Nebraska, in the Rocky Mountains to New Mexico, and on the Pacific Coast to California. Also in Patagonia, and in Europe and Asia. Summer. Cat's-tail. Witches'-milk. Paddock-pipes. Knotgrass.

2. Hippuris TetraphỳLla L. F. Four-Leaved Mare's-Tail

Fig. 3078

Hippuris tetraphylla L. f. Suppl. 81. 1781.

Hippuris maritima Hell. Dissert. Hippur. pl. 1. 1786.

Smaller than the preceding species. Stem 4-15' high; leaves obovate or oblanceolate, entire, in verticils of 4-6, not sphacelate at the apex or but slightly so, 4"-7" long.

Labrador and Quebec to Hudson Bay and Alaska. Also in northern Europe and Asia. Summer.