Aquatic or marsh plants, with small inconspicuous flowers, sessile in the axils of the leaves or bracts. Calyx-tube adherent to the ovary (but calyx and corolla wanting in Calli-triche), the latter 2-4-celled (in Hippuris of a single carpel). Limb of the calyx minute or none. Petals small or none. Stamens 1-8. Fruit indehiscent, a single seed in each cell.
1. Myrlopliyl'lum. Flowers monoecious or polygamous, with the parts in fours. Stamens 4 or 8. Immersed leaves pinnately dissected into capillary divisions.
2. Hippu'ris. Flowers perfect. Stamen, style, and carpel only oneLeaves entire, linear, acute; in whorls of 8 or 10.
3. Proserpina'ca. Flowers perfect, the parts in threes. Petals none. Stems creeping at the base. Leaves alternate, the immersed ones pinnately dissected.
4. Callit'riche, Flowers monoecious. Calyx and corolla wanting. Leaves entire, opposite. Staminate flower of a single stamen; pistillate flower a single 4-celled ovary. Fruit compressed, 4-lobed. 4-celled, breaking up into 4 one-seeded pieces.
1. M. spicatum, L. Stamens 8. Bracts ovate, entire, shorter than the flowers. Leaves in whorls of 3 or 4. Flowers greenish, in terminal spikes. Stems very long. - Deep water.
2. M. verticillatum, L. Stamens 8. Leaves finely dissected and whorled as in No. 1. Bracts pectinate-pinnatifid, much longer than the flowers, and the spikes therefore leafy. Stem 2-4 feet long. - Stagnant water.
3. M. heterophyl'lum, Michx. Stamens 4. Lower leaves dissected, in whorls of 4 or 5. Bracts ovate or lanceolate, finely serrate, crowded, the lower ones pinnatifid. Stem stout. - Stagnant or slow water.
4. M. tenel'lum, Bigel. Flowering stems nearly leafless. Bracts small, entire. Flowers alternate, monoecious. Stamens 4. - Borders of ponds.
L. Mare's Tail. H. vulga'ris, L. A perennial aquatic, with jointed erect stem. - Muddy margins of ponds and streams.
L. Mermaid-weed. P. palustris, L. (Mermaid-weed.) Low herb. Stem creeping at base. Leaves alternate, lanceolate, sharply serrate. Petals none. Stamens 3. Fruit nut-like, 3-seeded. - Wet swamps.
L. Water-Starwort. 1. C. Ver'na, L. Amphibious. Floating leaves obovate, tufted; submersed leaves linear. Flowers monoecious, axillary, usually between a pair of bracts. Sterile flower a single stamen; fertile flower a single pistil with a 4-celled ovary. Leaves beset with stellate scales.
2. C. autumna'lis. Growing under water. May be distinguished from C. verna by its leaves being retuse and all linear from a broader base, and its flowers without bracts.