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..
Annual glabrous or glabrate herbs, mostly with 4-angled stems, opposite sessile narrow leaves, and small axillary solitary or cymose flowers. Calyx campanulate, globose or ovoid, 4-angled, 4-toothed, often with small appendages in the sinuses. Petals 4 in our species, deciduous. Stamens 4-8, inserted on the calyx-tube, filaments slender or short. Ovary enclosed in the calyx-tube, nearly globular, 2-4-celled, bursting irregularly. [Named for Johann Ammann, 1699-1741, a German botanist.]
About 20 species, of wide geographic distribution, most abundant in warm regions. Besides the following, another occurs in the Southern States. Type species: Ammannia latifólia L.
Flowers sessile or very nearly so, solitary, or 2-3 together.
Leaves linear-lanceolate, acuminate; style elongated.
Leaves obovate or oblanceolate, obtuse; style very short
Flowers pedicelled, in axillary cymes.
Ammannia coccinea Rottb. Pl. Hort. Havn. Descr. 7. 1773.
Ammannia latifolia T. & G. Fl. N. A. 1: 480. 1840. Not L. 1753.
Erect, glabrous, branching below, 6'-20' high. Leaves linear-lanceolate, all obtusely cordate-auriculate and dilated at the somewhat clasping base, acuminate or acute at the apex, entire, 1'-3' long, 1"-3" wide; flowers 1-5 in each axil, sessile or very nearly so; petals purple, fugacious; style elongated, very slender, usually more than one-half the length of the capsule.
Ammannia humilis β T. & G. Fl. N. A. 1: 480. 1840.
Erect, glabrous, 6'-2o' high, at length freely branching. Leaves obovate, oblance-olate, or somewhat spatulate, obtuse or obtusish at the apex, the upper ones clasping and more or less auriculate at the base, the lower narrowed and sessile or tapering into a short petiole; flowers 1-3 together in the axils, sessile; petals pink, fugacious; stamens very short, not exserted; style very short; capsule enclosed by the calyx.
Erect, 2-10' high, at length widely branching. Leaves sessile, linear-lanceolate or oblong, acute or acutish at the apex, auriculate at the base, 1/2-1 1/2 long, about 2" wide; flowers in axillary peduncled cymes; pedicels 1/2"-1 1/2" long; petals purple; style slender; stamens exserted; cansule partly enclosed by the calyx.