Fruit usually markedly laterally flattened with a marginal rim or wing.
Aquatic herb similar to Ceratophyllum demersum, but usually more delicate, differing as follows: Leaves usually lighter green, 2–4 cm. long, branching dichotomously 3–4 times (rarely twice in some whorls), usually rather fine, 0.1–0.3 mm. thick, to 2.5 mm. thick in lower segments, marginal teeth few, inconspicuous, often absent from lower segments, up to 0.1–0.2 mm. long.
Male flowers to 2 mm. in diam.; anthers 0.6–0.8 x 0.4–0.7 mm., often smaller and relatively broader than in C. demersum.
Female perianth lobes (1.5) 1.8–2 x 0.1–0.3 mm., relatively narrower and usually longer than in C. demersum.
Mature fruit with apical spine less than 1 up to 9 mm.; surface sometimes with few large warts or spines.
Female perianth-segments usually longer, (1.5–)1.8–2 mm. long, 0.1–0.3 mm. wide, and relatively narrower (length (5–)7–10 times width).
Male flowers up to 2 mm. in diameter; mature anthers 0.6–0.8 mm. long, 0.4–0.7 mm. wide (length 1–1.5 times width).
Leaves usually lighter green, 2–4 cm. long, branched dichotomously 3–4 times, sometimes one part of leaf branched more than another, rarely a few leaves of whorl only twice branched, usually rather fine, 0.1–0.3 mm. in diameter, but lower 1–2 segments sometimes swollen and up to 2.5 mm. across, marginal spiny teeth always minute, less than 0.1 or 0.2 mm., on lower 2 segments few or absent, few or more rarely numerous on final 2 segments.