紫萍属 zi ping shu

Fronds free floating, 1-10 individuals coherent together, shiny green on upper surface, usually red on lower surface, outline usually asymmetric, flat on upper surface, rarely slightly gibbous on lower surface; 2 lateral pouches for reproducing daughter fronds and flowers present at base, bases of pouches surrounded by a small membranous scale covering bases of roots; veins 7-16(-21), splitting from node toward apex, sometimes visible on upper surface. Pigment cells present (visible in dried fronds as brown dots). Roots (5-)7-21, surrounded by a tubular sheath at base, enclosed by a rounded to pointed cap at apex. Daughter fronds connected to mother frond by a thin white stipe. Flower surrounded by a small, utricular, membranous scale with a narrow opening at apex; stamens 2, 4-locular. Seeds 1-3, ribbed longitudinally.

Two species: one species worldwide, the other restricted to Central and South America; one species in China.

Lower Taxon

• Spirodela polyrhiza (Linnaeus) Schleiden