1. Ammannia coccinea Rottb.

Pl. 448 i, j; Map 2031

Stems 10–40(–100) cm long. Leaves 1–8 cm long, 2–15 mm wide. Flower clusters usually with an evident stalk 3–4(–9) mm long, consisting of 3–5(–14) flowers, these with the stalk 0.5–2.0 mm long. Hypanthium plus sepals 2.5–4.0 mm long. Petals 1.5–2.3 mm long, deep pink to purple. Stamens 4(–7), the anthers deep yellow. Fruits 3.5–5.0 mm in diameter. 2n=66. June–October.

Scattered nearly throughout the state (eastern U.S. west to South Dakota and Texas; disjunct in Arizona and California; Mexico to South America, Caribbean Islands). Banks of streams, rivers, and spring branches and margins of ponds, lakes, swamps, and sloughs; also ditches, fallow fields, edges of crop fields, gardens, and open disturbed areas.

Ammannia coccinea commonly grows in muddy soils, often colonizing receding shorelines. Occasionally, it is found as an emergent aquatic in very shallow water. Graham (1979, 1985) demonstrated that this polyploid species originated as a hybrid between A. auriculata Willd. (2n=32) and A. robusta (2n=34), followed by a doubling of the chromosome number (to 2n=66) to restore fertility. Ammannia auriculata is a nearly cosmopolitan species with a distribution in the New World that extends northward through the central portion of the United States. It differs from both A, robusta and A. coccinea in being less robust, with more slender stems that usually are branched from well above the base; in having inflorescences with a slender stalk 3–9 mm long subtending a cluster of mostly 5–12 or more flowers; in having petals (similar in color to those of A. coccinea) 1.0–1.5 mm long; and in having fruits mostly less than 2.5 mm in diameter. Steyermark (1963) and many other botanists called plants A. auriculata that are now correctly determined as A. robusta.