Wolffia borealis

(Engelmann ex Hegelmaier) Landolt ex Landolt & O. Wildi

Northern Watermeal

Ber. Geobot. Inst. ETH, Stiftung Rubel 44: 137; 1977.

Description:

Shape of Plant Body: Ovoid-ellipsoid (longer than wide) with distinctly flattened, dark green dorsal surface (pitted with numerous stomata); apex more or less pointed (acute) and slightly upturned, floating with entire dorsal surface above water; lower submersed plant body is transparent green; brownish epidermal pigment cells (punctae) visible on dead or chlorotic plants; the pigment is a phlobaphene-like substance formed by oxidation and polymerization of phenolic compounds when the plant dies (like a freshly cut apple slice turning brown).

Size: 0.7-1.2 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: Occurring in widely separated disjunct populations throughout the Pacific, midwestern and Eastern United States, and southern Canada (Ontario and British Columbia); possibly introduced by migratory waterfowl into southern California (San Diego County).

Other Information:

See group comparison photo with Wolffia 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.

Selected Images:

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