Roots (1–)2–21 per frond, abaxial surface at node. Fronds floating (only turions sink to bottom), 2–10, coherent in groups, each obovate-circular, flat or gibbous, 1.5–10 mm, margins entire; air spaces in tissue; reproductive pouches 2, lateral, at base from which daughter fronds and flowers originate, triangular; veins (3–)5–16(–21), from point in proximal part of frond (node); small bifid 2-cleft membranous scale (interpreted as prophyllum) enveloping base of frond, covering point of attachment of roots; anthocyanins present (especially on abaxial surface); pigment cells present (visible in dead fronds as brown dots); turions present or absent, brownish olive, circular-reniform, smaller than growing frond. Flowers 1(–2) per frond, surrounded by small utricular, membranous scale; stamens 2, 4-locular. Seeds 1–3, longitudinally ribbed. x = 10, 18, 23.

Distribution

Nearly worldwide.

Discussion

Species 3 (2 in the flora).

Selected References

None.

Lower Taxa

Spirodela polyrrhiza, Spirodela punctata

Key

1	Fronds 1–1.5 times as long as wide, with 7–16(–21) veins and 7–21 roots, 1 or 2 perforating scale	Spirodela polyrrhiza
1	Fronds 1.5–2 times, as long as wide, with (3–)5–7 veins and (1–)2–7(–12) roots, all perforating scale.	Spirodela punctata