This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", 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..
Perennial relatively rigid herbs, with 4-angled erect or diffuse, but rarely creeping stems. Leaves opposite; blades toothed, narrowed at the base, pinnately nerved. Flowers solitary on slender axillary peduncles subtended by two small bractlets. Calyx not subtended by bract-lets; sepals 5, unequal, the upper one broadest; corolla white, purple or yellow, 2-lipped, the upper lip notched Stamens adnate to near the corolla-throat. Hypogynous disk wanting. Stigma 2-lobed. Capsule septicidal, the valves cleft. Seeds numerous. [Named in honor of Anton Meca y Cardona, a founder of the botanical garden at Barcelona.]
About 10 species, natives of warm and tropical America. Besides the following, some 4 others inhabit the southeastern United States. Type species: Mecardonia ovata R. & P.
1836. Monniera acuminata Kuntze, Rev. Gen. Pl. 463. 1891. Mecardonia acuminata Small, Fl. SE. U. S. 1065.
Perennial, glabrous; stem erect, branched above, 1°-2° high, very leafy. Leaves oblong or oblong-'anceolate, serrate, at least above the middle, short-petioled or sessile, obtuse or acute at the apex, narrowed or somewhat cuneate at the base, 1 -2' long, faintly veined; peduncles in alternate and opposite axils, ascending, in fruit longer than the leaves, not bracteolate at the summit; flowers 5"-6" long, purple or purplish; upper calyx-segment lanceolate, acute; corolla 2-lipped, the lower lip longer than the upper; stamens approximate in pairs; capsule oblong, 4-valved, 3"-4" high, about equalling the calyx.
In wet soil, Maryland to Florida, Missouri and Texas, mostly near the coast. Plant blackening in drying. June-Sept.