Herbs annual, robust, 3–10 dm. Stems: proximal branches often decumbent, length often equaling main-stem, unbranched, or branched near base. Leaf-blades usually lanceolate-linear, rarely spatulate, 15–80 × 4–15 mm. Inflorescences simple cymes, 1–3 (–5) -flowered mid-stem; peduncle stout, 0–0.5 mm. Pedicels 0. Floral-tube campanulate to urceolate, 3–5 mm; epicalyx segments as long as sepals; sepals 4 (–8); petals 4 (–8), pale lavender, sometimes with rose-purple midvein or rose-purple basal spot, 2–3 × 2.5–3.3 mm; stamens 4 (–8); anthers light yellow; style slender, well-exserted, 2 mm; stigma capitate. Capsules 4–6 mm diam., equal to or surpassing sepals, splitting irregularly. 2n = 34.

Phenology: Flowering late spring–late fall.
Habitat: Freshwater marshes, margins of pools and lakes, drying mud and sand flats, ditches, rice fields.
Elevation: 0–2100 m.

Distribution

• Generated Map
• Legacy Map

B.C., Ont., Ariz., Ark., Calif., Colo., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Mich., Minn., Mo., Mont., Nebr., Nev., N.Dak., Ohio, Okla., Oreg., S.Dak., Tenn., Tex., Utah, Wash., Wyo., Mexico, West Indies, Central America, South America, Pacific Islands (Guam)

Discussion

Ammannia robusta flowers spring through fall in the northern part of the range and year-round southward. The species has spread worldwide as a result of introduction through rice cultivation.

Ammannia robusta is documented for New Jersey by a collection from the mid 1800s (P. Knieskern s.n., NY); there is no evidence that it became established in the state.

Selected References

None.

Lower Taxa

None.