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Sagittaria rigida Pursh
Family: Alismataceae
sessile-fruited arrowhead
Sagittaria rigida image
Herbs, perennial, to 115 cm; rhizomes absent; stolons present; corms present. Leaves emersed or submersed; submersed leaves phyllodial, flattened, 30--70 cm, rarely widening into blade; emersed leaves phyllodial, flattened, or petiole triangular, 34--50 cm, blade linear to elliptic, rarely hastate to sagittate, 5--15 ´ 0.6--12 cm, basal lobes when present shorter than remainder of blade. Inflorescences racemes, of 2--8 whorls, emersed, 8--10 ´ 2--6 cm; peduncles 10--115 cm; bracts connate more than or equal to ΒΌ total length, ovate, 3--6 mm, delicate, not papillose; fruiting pedicels absent. Flowers to 3 cm diam.; sepals recurved, not enclosing flower; filaments dilated, shorter than anthers, pubescent; pistillate sessile to subsessile, without ring of sterile stamens. Fruiting heads 1--1.7 cm diam.; achenes obovoid to oblong, abaxially keeled, 2--3 ´ 1.3--1.6 mm, beaked; face not tuberculate, wings 1--2, ± entire, glands 1; beak lateral, recurved, 0.8--1.4 mm. 2n = 22. Flowering summer (Jul--Sep). Calcareous or brackish shallow water and shores of ponds, swamps, and rivers, occasionally in deep water; 0--1000 m; Man., Ont., Que., P.E.I., Sask.; Ark., Calif., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Nebr., N.H., N.J., N.Y., Ohio, Pa., R.I., Tenn., Vt., Va., Wash., W.Va., Wis.
Perennial aquatic herb to 1.15 m tall Leaves: emersed or submersed. Submersed leaves are 30 cm - 0.7 m long and linear. Emersed leaves on triangular stalks 34 - 50 cm long, linear to elliptic (rarely arrowhead-shaped), 5 - 15 cm long, 0.6 - 12 cm wide, with lobes (when present) narrow and shorter than rest of blade. Inflorescence: emersed, singly stalked along a central axis (raceme), 8 - 10 cm long, 2 - 6 cm wide, arising from a 10 cm - 1.15 m stalk that is usually bent at the lowest whorl, with two to eight whorls of flowers. Flowers: either male or female, found on the same plant (monoecious), with recurved sepals 4 - 7 mm long and three white petals 1 - 3 cm long. Male flowers are borne near the top of the inflorescence, having scaly filaments shorter than the anthers. Female flowers found near base of inflorescence, stalkless or short-stalked. Fruit: a spherical cluster of achenes 1 - 1.7 cm wide. Each achene 2 - 3 mm long, 1.3 - 1.6 m wide, oblong to inversely egg-shaped, with a horizontal and recurved beak 0.8 - 1.4 mm long. Bracts: 3 - 6 mm long, egg-shaped, delicate, fused at least one-quarter the length.

Similar species: Sagittaria rigida and Sagittaria graminea almost always lack the arrowhead-shaped leaves of the other Sagittaria species growing in the Chicago Region. Both species nearly always have linear to lance-shaped or narrow egg-shaped leaves as well as flowers with scaly filaments. Sagittaria graminea does not have a bent inflorescence stalk, the flower stalks are usually longer than 1 cm, and the achenes have beaks that are shorter than 0.8 mm.

Flowering: mid June to mid September

Habitat and ecology: Muddy borders of streams and ditches, shallow water, swamps, margins of ponds, and along waterways.

Occurence in the Chicago region: native

Etymology: Sagittaria comes from the Latin word sagitta, meaning arrow, referring to the leaf shape. Rigida means rigid.

Author: The Morton Arboretum

Erect or lax, emersed or submersed, highly variable according to the habitat; lvs lanceolate and entire, or shortly sagittate with narrow basal lobes, or phyllodial; scape 1-8 dm, with 2-8 whorls of fls, typically geniculate at the lowest whorl, the upper fls staminate on filiform pedicels 1.5-3 cm, the lower pistillate, sessile or nearly so (the pedicel sometimes to 5 mm, rarely to 1 cm); bracts ovate, obtuse, 4-6 mm, connate below, smooth; sep ovate, 4-7 mm, reflexed at maturity; pet 1-3 cm; stamens 15-many; filaments subulate, roughened with minute scales; achenes obovate to oblong, 2-3 mm, narrowly winged on the margins only, usually with a resin-duct on each face; beak 0.8-1.4 mm; 2n=22. In shallow water of swamps and ponds; Me. and Que. to Minn., s. to Va., Tenn., Mo., and Neb. July-Sept. (S. heterophylla)

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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