Wayne Armstrong's On-line Description of Spirodela polyrrhiza (Lemnaceae)
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Spirodela polyrrhiza

(L.) Schleiden

Greater Duckweed

Linnaea 13: 392; 1839.

Description:

Roots: 5 (7)-16 (rarely more)

Shape of Plant Body: Flattened, orbicular-ovate in outline; green above with reddish-purple ventral surface.

Size: 10 mm long.

Veins: 7-12 (15)

Budding Pouch Position: 2 lateral pouches on either side of basal end.

Flower (Fruit) Position: Within membranous, saclike spathe (open only at top) inside budding pouches.

Arrangement of Clonal Clusters: Solitary or 2-5 connected; producing smaller, rootless, dark green or brownish daughter plants (turions) during fall; the dense, starch-filled turions settle to bottom and overwinter.

Habitat: Fresh water ponds, marshes and quiet streams.

Range: Widely distributed throughout the western United States from sea level to 2500 m; widespread in North and Central America, Europe, Africa, Asia and northern Australia; in South America mostly replaced by S. intermedia W. Koch.

Other Information:

Largest of all North American duckweeds; the large (10 mm), rounded plant body with reddish-purple ventral surface and multiple roots is easily distinguished from all Lemna spp.; readily separated from Landoltia punctata by larger, more orbicular plant body and numerous roots (generally more than 5); one root (rarely 2) penetrating the scalelike (leaflike) ventral prophyllum.

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