1. Najas flexilis
(Willd.) Rostk. & F.W. Schmidt (northern naiad)
Pl. 110 g, h; Map 450
20–50 cm long. Leaves 1–3 cm long, 0.2–0.6 mm wide, ascending to spreading,
minutely serrulate with 1‑celled teeth usually visible only with
magnification, the tip acute to acuminate. Leaf bases gradually broadened into
stipular sheaths, the sheaths not auriculate. Seeds 2.5–3.7 mm long, elliptic
to narrowly obovate, not curved at the tip, the surface yellow to reddish
brown, shiny, finely and indistinctly pitted with 30–50 rows of 4–6‑sided
pits. 2n=12, 24. July–September.
known only from historical collections from Boone County (U.S. and Canada, south to Utah and Maryland). Submerged aquatic in lakes.
species is apparently sensitive to changes in water quality (Wentz and Stuckey,
1971) and has disappeared from a number of sites within its range, including
the Missouri populations, as waters have become polluted.