In Rataj's taxonomy, E. trialatus is in Section Paniculati, Subgenus Echinodorus.

Stem erect, along the whole length distinctly alate (three-winged), 30–70 cm (12–28 in) long.

Bracts longer than the pedicels with flowers, 1.5–2 cm (1–1 in) long having 19–21 distinct ribs.

Sepals about 5 mm long, with usually 18 ribs, corolla white.

Achenes 2.5–3 mm (0.098–0.118 in) long by 1–1.2 mm (0.039–0.047 in) wide, distinctly ribbed only in the lower part of the body, the upper third without ribs, lateral glands absent.