Wayne Armstrong's On-line Description of Wolffia borealis (Lemnaceae)
Home Keys To Genera List Of Species Search Lemna Spirodela Wolffia Wolffiella Wayne's Word

Wolffia borealis

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

Northern Watermeal

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


Roots: None.

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:

May be distinguished from other North American Wolffia spp. by its distinctly flattened dorsal surface with pointed, slightly upturned apex (and brown pigment cells on dead plants); when viewed from above with substage illumination only, live plants appear darker compared with other transparent green spp. without dark green dorsal surface.

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:

Return To The Lemnaceae Home Page
Go To Keys To The Genera Of Lemnaceae
Go To The List Of Species Of Lemnaceae
Go To The List Of .GIF Images Of Lemnaceae
Go To The WAYNE'S WORD Home Page