This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs, our species annual, with opposite entire membranous leaves, and minute stipules, or the leaf-bases connected by a stipular line. Flowers small, whitish, in one-sided spikes forming terminal or axillary cymes. Calyx 5-parted. Corolla urn-shaped, 5-lobed, the lobes valvate in the bud. Stamens 5, included; filaments short; anthers cordate. Ovules numerous, on peltate placentae; style short, 2-divided below, united above by the common stigma, the divisions becoming separate. Capsule 2-lobed at the summit; carpels divaricate, dehiscent along the inner side. Seeds numerous, small, tuberculate. [Greek, dog-killing.]
About 5 species, natives of warm and tropical regions. Type species: Cynoctonum sessili-folium J. G. Gmel.
Ophiorhiza Mitreola L. Sp. Pl. 150. 1753. Anonymos petiolata Walt. Fl. Car. 108. 1788. Cynoctonum petiolatum Gmel. Syst. 2: 443. 1791. Mitreola petiolata T. & G. Fl. N. A. 2: 45. 1841. Cynoctonum Mitreola Britton, Mem. Torr. Club 5: 258. 1894.
Stem simple, or branched near the base, or sometimes also above, glabrous, slender, erect, terete, 1°-2° high. Leaves lanceolate or ovate, petioled, 1'-3' long, 3"-1' wide, acute at both ends, glabrous; cymes terminal and often also in the upper axils, slender-peduncled, the divisions slender, simple or forked; flowers about 1" broad, numerous, sessile or very nearly so; capsule deeply 2-lobed, compressed, the lobes at length widely diverging, acute, dehiscent by a slit in the ventral suture near the summit.
In wet or moist soil, Virginia to Florida, Texas and Mexico. Also in the West Indies. June-Sept.