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

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Wolffia globosa

(Roxburgh) Den Hartog and Van der Plas

Tropical Watermeal

Blumea 18: 367; 1970

Description:

Roots: None.

Shape of Plant Body: Ovoid or ellipsoid-cylindrical (longer than wide) and transparent green throughout (some populations may contain individuals with darker green dorsal surface); dorsal surface rounded on edges with upper central portion flattened, floating with only the central portion of dorsal surface above water; without brown epidermal pigment cells.

Size: 0.4-0.9 mm long; the smallest of all known flowering plants, rivaled in minuteness only by the Australian sp. W. angusta Landolt.

Veins: None.

Budding Pouch Position: One funnel-shaped pouch at basal end; budding pouch often with distinct collar of elongate cells at junction with daughter plant.

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 confined to ponds and ditches of hot interior valleys of central and southern California at low elevations, and in sloughs along rivers draining the western slopes of the Sierra Nevada; may have been introduced into California, perhaps in rice fields of Central Valley; outside of California the only other location for this sp. in the United States is Pinellas County, Florida; worldwide distribution in tropical regions including southern Florida (Pinellas County), Africa, India, Southeast Asia, Malaysia, Philippines and Hawaiian Islands; this sp. is the edible "khai-nam" or "water eggs" of Thailand.

Other Information:

May be distinguished from the similar and closely related W. columbiana by its smaller size and more cylindrical, flat-topped plant body; this sp. sometimes appears darker green on the dorsal surface, but may be distinguished from W. borealis by its smaller size, more rounded upper surface and apex (not as distinctly flattened and pointed), and lack of brown pigment cells.

See a comparison photo with Wolffia globosa (2) and W. columbiana (3) 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.

South African populations of W. globosa (Roxb.) Hartog & Plas are now recognized as W. cylindracea Hegelm., an older name used in the literature since Hegelmaier (1868). The widespread Asian W. globosa (also from California and southern Florida) has been retained as W. globosa. Although the two species are similar morphologically, W. globosa has a translucent edge or margin (visible from above). This translucent edge is not present in W. cylindracea.

Selected Images:

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