Sagittaria isoetiformis
quillwort arrowhead
emersed or submersed, phyllodial or rarely dilated apically, flattened, 4–40 cm × 0.05–0.4(–0.5) cm.
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.
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.
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.
Sagittaria isoetiformis
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.).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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