Herbs aquatic with the habit of seaweeds, with alternate, dissected leaves, with flowers minute, perfect, naked or with 3 sepals, stamens 1 or many, hypogynous.

Ovary compound, 2 to 3-celled, with as many stigmas, and numerous ovules. Fruit a many-seeded capsule, ribbed and somewhat pedicelled. Albumen none.

Genera 20, species 100. frequent in S. America and E, India. 1 only in N. America. They all prow in running water, attached to stones like the following species.

PODOSTE'MUM, L. C. Rich. Threadfoot. River Weed. (Gr.Order CXXV Podostemiaceae Threadfoots 1831Order CXXV Podostemiaceae Threadfoots 1832 a foot, Order CXXV Podostemiaceae Threadfoots 1833 the stamens being apparently on a common foot-stalk,) Stamens 2, with the filament3 united below; ovary oblong-ovoid; stigmas 2, sessile recurved; capsule 2-celled; seeds minute. - Small, submersed herbs, adhering to stones and pebbles.

P. ceratophyllum Mx Lvs. dichotomously dissected; fls. solitary, axillary. - Mid. W. and S. States, in shallow streams. St. a few inches long, usually destitute of roots and attached to stones by lateral, fleshy processes. Lvs. numerous, olive-green, alternate, coriaceous, divided into many long, linear-setaceous segments. Fls. on short, thick peduncles, the 2 stamens and styles at length bursting through the lacerated calyx. Jl. (Lacis ceratophylla Bougard.)