Wolffia arrhiza

(Linnaeus) Horkel ex Wimmer

Common Watermeal

Fl. Schles. 3: 140; 1857.

Description:

Shape of Plant Body: Ovoid to nearly spherical with a distinctly flattened, dark green dorsal surface (transparent below), floating with only central portion of dorsal surface above water; without brown pigment cells.

Size: 0.8-1.3 mm long.

Veins: None.

Budding Pouch Position: One funnel-shaped pouch at basal end.

Flower (Fruit) Position: Within floral cavity on dorsal surface, not enclosed by a spathe.

Arrangement of Clonal Clusters: Solitary or 2 connected.

Habitat: Floating at surface of quiet streams and ponds, often mixed with other Lemnaceae and aquatic plants.

Range: Rare in California and probably introduced, generally in mild coastal and interior valleys of central and southern California; not known north of California or elsewhere in the United States; wide distribution throughout temperate, subtropical and tropical regions of Europe, Africa, western Asia and eastern Brazil.

Other Information:

See group comparison photo with Wolffia arrhiza (6), W. brasiliensis (4) and W. borealis (5) next to each other. The transparent green species without dark green dorsal surface, W. globosa (2) and W. columbiana (3), appear darker because of the above-stage illumination. The reverse is true when viewed with substage illumination only. I.e. W. arrhiza appears darker and W. columbiana appears lighter and more translucent (see backlit image) of these latter two species.

Selected Images:

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