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

H.A. Weddell

Brazilian Watermeal

Ann. Sci. Nat. 12: 170; 1849.


Roots: None.

Shape of Plant Body: Ovoid-ellipsoid (longer than wide) with flattened, dark green dorsal surface (pitted with numerous stomata) containing a conical central papule (the papule may vary from a tiny raised point to a prominent volcano-like cone covering the upper surface); apex rounded (not acute); 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, ponds, sloughs and marshes, often mixed with other Lemnaceae and aquatic plants.

Range: Widely disjunct populations in ponds and marshlands of California (Sacramento Valley), Oregon (Willamette Valley) and Washington (Thurston County); since this tropical species was previously unknown in these locations prior to 1988, it may be a recent introduction; more commonly distributed in southern and southeastern United States, extending southward into Mexico, Central and South America.

Other Information:

May be distinguished from the similar and closely related W. borealis (Hegelm.) Landolt & Wildi by its conical central papule on dorsal surface, slightly wider body and rounded apex (not pointed and slightly upturned as in W. borealis); the brown pigment cells on dead plants distinguish this sp. from all other North American Wolffia spp. (with the exception of W. borealis); 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:

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