Wayne Armstrong's On-line Description of Wolffia columbiana (Lemnaceae)
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Wolffia columbiana


Colombia Watermeal

Bot. Unters. 1: 103; 1865


Roots: None.

Shape of Plant Body: Ovoid or nearly spheric and transparent green throughout, dorsal surface mostly rounded (with flattened area in center); floating with only the central portion of dorsal surface above water, the rest of plant body submersed; 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: Generally at low elevations in Pacific, midwestern and eastern United States, Canada (Manitoba, Ontario and Quebec), extending sporadically south in Mexico, Central and South America.

Other Information:

May be distinguished by its larger, spheroid, transparent green plant body with a dorsal surface that is mostly rounded with a flat spot in the center; smaller individuals may be confused with W. globosa (Roxb.) Hartog & Plas which has a more cylindrical and flat-topped transparent green body; the very similar and closely related W. arrhiza (L.) Wimmer has a more conspicuously flattened, dark green dorsal surface which appears darker when viewed from above with substage illumination only; in addition, the dorsal surface of W. columbiana has 1-10 (15) stomata, while W. arrhiza has 15-100 stomata.

See a comparison photo with Wolffia columbiana (3) and W. globosa (2) next to each other. These transparent green species without dark green dorsal surface appear darker because of the above-stage illumination. Species with dark green dorsal surface appear lighter with above-stage illumination, including W. brasiliensis (4), W. borealis (5), and W. arrhiza (6). 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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