四叶杉叶藻 si ye shan ye zao

Stems 10-50 cm. Leaves (2-)4(-6)-whorled, ovate, elliptic, or lanceolate, 0.4-1.2 × 0.5-0.7 cm, fleshy, margin entire, apex subacute; submerged leaves shorter than emergent leaves. Flowers purplish. Stamens ca. 1 mm. Achene ovoid. Fl. and fr. Aug.

Bogs, salt marshes. NE Nei Mongol (Mangui) [Japan; Europe, North America].

This species is very similar to Hippuris vulgaris but is traditionally separated by its shorter, 4-whorled leaves. These characters are to some extent under environmental control, being present at low temperatures or high salinity. Hippuris tetraphylla is commonly recognized in Europe and North America but less so in Asia.