Ammannia robusta

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

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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.