Quillwort Arrowhead

Sagittaria isoetiformis has often been misidentified as Sagittaria teres (E. O. Beal 1960b). The two species can be separated, however: S. teres has nearly terete phyllodia, whereas S. isoetiformis has flattened phyllodia (R. K. Godfrey and P. Adams 1964). A study of the genetics of the two species shows them to be genetically different, and the data indicate the two taxa actually should be considered at the specific level. The two species are capable of CAM photosynthesis, a process very uncommon in the genus and found among none of their supposedly closely related species (A. L. Edwards, pers. comm.).

Herbs, perennial, to 65 cm; rhizomes absent; stolons present; corms present. Leaves emersed or submersed, phyllodial or rarely dilated apically, flattened, 4--40 cm ´ 0.05--0.4(--0.5) cm. Inflorescences racemes, of 1--5 whorls, emersed, 2--20 ´ 1.5--12 cm; peduncles 7--59 cm; bracts connate more than or equal to ¼ total length, oblanceolate, 0.2--0.3 mm, delicate, not papillose; fruiting pedicels spreading, cylindric, 0.5--6 cm. Flowers to 1.3 cm diam.; sepals recurved to spreading, not enclosing flower; filaments dilated, shorter than anthers, minutely tomentose; pistillate pedicellate, without ring of sterile stamens. Fruiting heads 0.5--1 cm diam.; achenes obovoid, abaxially keeled, 2.2--2.8 ´ 1.5--2 mm, beaked; faces not tuberculate, wings 1--2, ± entire, glands 3--5; beak lateral, incurved-erect, 0.2 mm.

Ala., Fla., Ga., N.C., S.C.

Flowering summer--fall.

Shores of sandy-bottomed lakes, se coastal plain; 0--100m.

Sagittaria isoetiformis J. G. Smith, Rep. Mo. Bot
Gard. 6 : 115. 1895.
Plants more or less submerged, 1-3 dm. tall ; leaves represented by terete, long and slenderly attenuate phyllodia, which occasionally develop thick, imperfect blades ; scapes 1-3 dm. tall, or rarely less, as long as the leaves or overtopping them ; whorls of the inflorescence one to three ; bracts ovate, 2-3 mm. long, acute, united below ; pedicels of the pistillate flowers slender, 15-18 mm. long, those of the staminate flowers filiform, often longer than the former ; sepals becoming 3-4 mm. long ; corolla 12-15 mm. broad ; filaments ovate, pubescent, about as long as the anthers ; anthers suborbicular ; fruit-heads about 6 mm. in diameter ; achenes obovate, 1.5 mm. long, with the dorsal and ventral margins ridged and several broad facial ridges, the short beak erect or oblique, near the top of the achene-body.
Type locality : Kustis, Lake County, Florida. Distribution : Georgia and Florida.

Sagittaria isoetiformis, common name quillwort arrowhead, is an aquatic plant species native to Cuba and to the southeastern United States (Florida, Alabama, Mississippi, Georgia, North Carolina and South Carolina).

Sagittaria isoetiformis is similar to Sagittaria tenuis and often mistaken for it, but Sagittaria isoetiformis has flattened leaves rather than leaves round in cross-section. Leaves of both species are usually submerged but sometimes emerging from the water.