Stems often profusely branched distally, 11--90 cm ´ 0.1--2 mm; internodes 0.1--9 cm, without prickles. Leaves spreading with age, 0.3--3.3 cm, lax in age; sheath 1--3.4 mm wide, apex rounded to truncate; blade 0.2--2.1 mm wide, margins minutely serrulate, teeth 18--100 per side, apex rounded to truncateslightly auriculate, with 1--3 teeth, teeth unicellular; midvein without prickles abaxially. Flowers 1--3 per axil, staminate and pistillate on same plants. Staminate flowers in distal axils, 1.5--3 mm; involucral beaks 4-lobed, 0.2--1.3 mm; anther 1- or 4-loculed, 1--1.7 mm. Pistillate flowers in proximal axils, 1.5--4 mm; styles 0.3--1.5 mm; stigmas 4-lobed. Seeds not recurved, yellowish white with purple tinge, fusiform, 1.2--3.8 ´ 0.4--0.8 mm, apex with style situated at center; testa dull, 3 cell layers thick, pitted; aeroleareoles regularly arranged in 20--60 longitudinal rows, not ladderlike, 4--6-angled, longer than broad, end walls not raised. 2n = 12, 36, 42, 48, 54, 60. By having unicellular teeth on the leaf margin, Najas guadalupensis resembles N. flexilis and N. graminea. The seeds of N. guadalupensis are pitted; those of N. flexilis are smooth. The sheaths of N. guadalupensis are rounded to slightly auriculate; those of N. graminea are deeply auriculate.
Monoecious; stems profusely branched, 1-8 dm; lvs 0.5-3 cm נ0.2-2 mm, spreading, not so sharply pointed as in our other spp., with sloping shoulders at the base, minutely serrulate with 20-100 unicellular teeth per side; anthers dithecal, with 4 microsporangia; style apical; seeds 1.2-2.5 mm, purple-tinged, fusiform, pitted, the areolae 4-6-angled, about as long (0.08-0.1 mm) as wide, in 20-40 rows; 2n=12, 36, 48, 54, 60. Widespread in N. and S. Amer., n. to Me., s. Que., Man., Alta., and Wash. The widespread var. guadalupensis, slender, with stems 0.2-1 mm thick, and with 50-100 teeth on each side of the lf, tends to give way at the n. to var. olivacea (Rosend. & Butters) R. R. Haynes, which occurs from N.Y. and s. Que. to n. Ind., n. Io., and s. Man., and is stouter, with stems mostly 1-2 mm thick, and with 20-40 teeth per side of the lf. (N. olivacea)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.