1. R. Virgínica, L. _Stem square_, with wing-like angles; _leaves oval-lanceolate, sessile, acute_; calyx-tube and pedicels more or less hispid with gland-tipped hairs; petals bright purple.--Sandy swamps; coast of Maine to Fla., west to northern N. Y., Ind., Mo., and La. Slender rootstocks tuberiferous. 2. R. aristòsa, Britt. Branches somewhat wing-angled; leaves linear-oblong, sessile, not narrowed at base, naked or very sparsely hairy; hairs of the calyx mostly below the throat, not gland-tipped; petals sparsely villous, bright purple.--Egg Harbor City, N. J. (_J. E. Peters_); also Sumter Co., S. C. (_J. D. Smith_). 3. R. Mariàna, L. _Stems cylindrical; leaves linear-oblong_, narrowed below, mostly petiolate; petals paler.--Sandy swamps; N. J. to Fla., west to Mo. and La. [*][*] _Anthers oblong, straight, without any spur; flowers few, sessile._ 4. R. ciliòsa, Michx. Stem square, glabrous; leaves broadly ovate, ciliate with long bristles; calyx glabrous.--Md. to Fla. and La. ORDER 41. LYTHRÀCEÆ. (LOOSESTRIFE FAMILY.) _Herbs, with mostly opposite entire leaves, no stipules, the calyx enclosing but free from the 1--4-celled many-seeded ovary and membranous capsule, and bearing the 4--7 deciduous petals and 4--14 stamens on its throat; the latter lower down. Style 1; stigma capitate, or rarely 2-lobed._--Flowers axillary or whorled, rarely irregular, perfect, sometimes dimorphous or even trimorphous, those on different plants with filaments and style reciprocally longer and shorter. Petals sometimes wanting. Capsule often 1-celled by the early breaking away of the thin partitions; placentæ in the axis. Seeds anatropous, without albumen.--Branches usually 4-sided. [*] Flowers regular or nearly so. [+] Flowers mostly solitary in the axils of the leaves, sessile or nearly so. 1. Didiplis. Calyx short, without appendages. Petals none. Stamens 4. Capsule indehiscent. Small aquatic. 2. Rotala. Calyx short, the sinuses appendaged. Petals and stamens 4. Capsule septicidal, with 3--4 valves. 3. Ammannia. Flowers not trimorphous. Petals generally 4 or none. Stamens 4. Capsule bursting irregularly. [+][+] Flowers in 3--many-flowered axillary cymes (rarely solitary). 4. Lythrum. Calyx tubular. Petals usually 6. Stamens mostly 6 or 12. Flowers cymose-spicate in one species. 5. Decodon. Flowers trimorphous. Petals 5 (rarely 4). Stamens 8--10. Capsule 3--4-valved, loculicidal. [*][*] Flowers irregular and unsymmetrical, with 6 petals and 11 stamens. 6. Cuphea. Calyx spurred or enlarged on one side at base. Petals unequal. 1. DIDÍPLIS, Raf. WATER PURSLANE.