Ammannia koehnei Britton; A. koehnei var. exauriculata Fernald; A. teres Rafinesque var. exauriculata (Fernald) Fernald

Herbs annual, robust, 4–10 dm. Stems erect, sparsely branched, or branched proximally. Leaf blades lanceolate-linear to oblong, elliptic, or spatulate, 15–70(–100) × 4–15(–21) mm. Inflorescences simple cymes, (1–)3–10-flowered mid stem; peduncle stout, 3 mm. Pedicels 0–1 mm. Floral tube urceolate, 3–4 mm; epicalyx segments as long as or slightly longer than sepals; sepals 4(–6), shallowly deltate, with mucronate apex; petals 0–4(–6), pale pink to white, 1 × 1 mm; stamens 4(–8); anthers yellow; style stout, included, ca. 0.5 mm; stigma capitate. Capsules 3.5–5.5 mm diam., included to scarcely surpassing sepals, splitting irregularly. 2n = 48.

Flowering late spring–late fall. Coastal plains in brackish to freshwater marshes, ditches; 0–200 m; Fla., Ga., La., Md., Miss., N.J., N.C., S.C., Tex., Va.; Mexico (Yucatán); West Indies; Central America (Panama); South America.

Ammannia latifolia flowers spring through fall in the northern part of the range; year-round from southern Florida southward.

Petals in Ammannia latifolia are consistently present from the Gulf Coast and from Georgia northward along the Atlantic Coast, and are commonly reduced in number or absent along the southern Atlantic and Gulf coasts and southward. Presence of petals is best determined in the bud.