Najas guadalupensis (Spreng.) Magnus subsp. guadalupensis, common water–nymph. Annual, submersed aquatic, clonal via fragmentation forming dense mats and colonies, fibrous–rooted (lower nodes), much–branched throughout, repeatedly forked and typically with unequal, diverging branches having 1 flower in axil of the narrower axis; monoecious; shoots glabrous, lacking stomates.
Stems cylindric and slender, 0.5—1 mm diameter, internodes to 40 mm long.
Leaves subopposite (visually opposite), 1 = cauline leaf (upper leaf) subtending main shoot + 1 = bract subtending flower or a leaf of a future lateral shoot (lower leaf), simple with sheath, sessile, without stipules; sheaths at node slightly dimorphic, open, roundish, of cauline leaf fully sheathing and ca. 3 mm long, of bract partially sheathing and ca. 2 mm long, minutely serrate (= 1–celled teeth) on margins, the teeth aging brownish, rounded to oblique (not lobed or auriculate) at shoulders beneath blade and with several larger teeth along edge; blade narrowly linear, 10—20(—25) × (0.5—)1—1.5(—2) mm, the widest at base, flat, minutely toothed on margins, acute typically with 1 or more minute teeth at tip, 1–veined.
Inflorescences solitary unisexual flowers, axillary, bracteate, glabrous; bract paired with cauline leaf, leaflike (described above); bractlet (staminate flower) spathelike and sheathing, ca. 3 × 0.8 mm, membranous and pale green; pedicel (staminate flower) 0.2—0.3 mm long (forming at anthesis).
Staminate flower perianth absent; stamens 1, free, sessile; anther dithecal, broadly ellipsoid, ca. 2.5 mm long, white, longitudinally dehiscent; pollen white; pistil absent.
Pistillate flower perianth absent; stamens absent; pistil 1; ovary superior, narrowly fusiform, 2.5—2.8 × 0.6 mm, 1–chambered with 1 basal ovule; stigmas 2(—3), lanceolate, usually with 2 sterile, spiny processes, the spines > stigmas, transparent except for reddish at tip.
Fruit utriclelike achene, indehiscent, 1–seeded, ± narrowly fusiform or ellipsoid, 2.5—3 mm long, colorless to purplish red and thin–walled, free from seed.
Seed same shape as fruit, ± 2 × 0.6—0.7 mm, dull tannish, pitted with longitudinal rows of collapsed cells.
A. C. Gibson & B. A. Prigge