Linnaea 13: 391. 1839.

Common names: Duck-meal
Etymology: Greek speira, winding, and delos, distinct
Treatment appears in FNA Volume 22. Treatment on page 145.

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.


Nearly worldwide.


Species 3 (2 in the flora).

Selected References



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