16.
Sagittaria rigida
Pursh, Flora Americae Septentrionalis. 2: 397. 1814.
Sessile-fruited arrowhead, Sagittaire dressee
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 ¼ 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.
