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Alisma subcordatum Raf.
Family: Alismataceae
American water plantain,  more...
[Alisma plantago-aquatica subsp. subcordatum (Raf.) Hultén,  more]
Alisma subcordatum image
Herbs, to 6 dm. Leaves emersed, rarely floating, petiolate; blade ovate to elliptic, to 15 ´ 10 cm. Inflorescences to 1 m. Flowers chasmogamous; sepals 1.5--2.5(--6) mm; petals white, 1--3 mm, margins slightly erose, apex mostly acuminate; anthers rounded, 0.4--0.6 mm; style ± curved, 0.2--0.4 mm, ¼ length ovary. Fruiting heads 2--4 mm diam; achenes obliquely ovoid, 1.5--2.2 mm, abaxially rounded, with 1 abaxial groove; beak ascending. 2n =14. Flowering spring--fall. Shallow ponds, stream margins, marshes, and ditches; 50--1500 m; N.B., Ont., Que.; Ala., Ark., Colo., Conn., Del., D.C., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn. Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., W.Va., Wis.; Mexico.
Perennial aquatic herb to 0.6 m tall Leaves: emersed (rarely floating), triangular-stalked, to 18 cm long and 12 cm wide, egg-shaped to elliptic. Inflorescence: loosely branched (panicle), terminating a stalk to 1 m long. Flowers: bisexual, with 1.5 - 2.5 mm long sepals. The three white petals are 1.3 - 2.5 mm long with a long pointed tip and slightly unevenly cut margins. Fruit: a cluster of achenes 2 - 4 mm in diameter. Each achene has an ascending beak, is 1.5 - 2.2 mm long, and has a rounded outer edge with a single groove.

Similar species: The similar Alisma triviale has flowers greater than 4 mm across and achenes greater than 2 mm long.

Flowering: early July to early September

Habitat and ecology: Frequent in marshes, shallow water, and ditches.

Occurence in the Chicago region: native

Etymology: Alisma is the classical Greek name for the water plantain. Subcordatum means "somewhat heart-shaped."

Author: The Morton Arboretum

Much like no. 1 [Alisma triviale Pursh], but with smaller fls; sep 1.5-2.3 mm; pet 1.8-2.5 נ1.4-2.0 mm, barely or scarcely longer than the sep; anthers 0.4-0.6 mm; style very short, 0.2-0.4 mm; achenes 1.5-2.2 mm; 2n=14. Usually in shallow water; Vt. and Mass. to N.D., s. to Fla. and Tex. (A. plantago-aquatica var. parviflorum) Variously reported to intergrade with no. 1 or to be genetically isolated from it.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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