On-Line Key to the Genus Wolffia
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Lemnaceae

Genus: Wolffia

Keys To This Genus

Plant bodies minute and rootless, with granular or mealy texture when rubbed between fingers of hands; generally globoid to ovoid-ellipsoid or cylindrical (flat-topped in some species); 0.4-1.3 mm long and 0.2-1.0 mm wide, floating on or partially below water surface; veins 0; pale transparent green throughout or with dark green dorsal surface; some species punctate with brown pigment cells in epidermis (visible on dead plants of W. borealis & W. brasiliensis); solitary or with smaller daughter plant attached at basal end; single, funnel-shaped budding pouch at basal end; daughter plants produced in basal budding pouch (in most species, some daughter plants may sink to bottom and function as overwintering turions); parenchyma without druse or raphide crystals of calcium oxalate; one bisexual flower produced inside dorsal floral cavity, consisting of a single pistil and single stamen (some authorities consider this to be an inflorescence with 2 unisexual flowers); pistil situated nearest the basal budding pouch; anther unilocular and apically dehiscent along pigmented line; ovary unilocular with one orthotropous ovule; utricle globose and slightly compressed, bearing 1 globose-ovoid, smooth seed with distinct conical operculum (seed may be slightly reticulate but not longitudinally ribbed); size and shape of plant body important for species identification (ideally under 10-20X magnification); at least 9 spp. worldwide, especially warm temperate and tropical regions; J.F. Wolff, German botanist and physician, 1778-1806; Armstrong, W.P. & R.F. Thorne (1984), Madrono 31: 172-179; Armstrong, W.P. (1989), Madrono 36: 283-285; Armstrong, W.P. (1985), Fremontia 13: 11-14.

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