On-Line Key to the Genus Wolffiella
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Lemnaceae

Genus: Wolffiella

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Plant body thin-membranous and flattened (thalluslike), oblong, broadly lingulate to narrow-linear (sabre-shaped to falcate in W. gladiata), rootless, 3-9 (10) mm long and 0.5-5 mm wide, often with free ends curved downward (recurved); floating just below water surface, often beneath other aquatic plants (basal, upper surface of flowering plants emersed); veins 0 (except for costa in budding pouch); pale transparent green with enlarged air spaces (aerenchyma) at basal end, often punctate with brown pigment cells in epidermis; solitary or with one daughter plant attached at basal end (in some species star-shaped clusters of 8 or more remain attached); single triangular, dorsi-ventrally flattened budding pouch at basal end, with tract of elongated cells (costa) on ventral surface of pouch (between midline and edge); daughter plants produced in basal budding pouch, no turions produced (undoubtedly limiting the distribution to warmer regions); parenchyma without druse or raphide crystals of calcium oxalate; one bisexual flower produced inside dorsal floral cavity, toward basal end of plant body, lateral (right or left) to the midline, 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 1 orthotropous ovule which often becomes tilted; utricle globular-ellipsoid and slightly compressed, bearing a single, smooth, globoid-ellipsoid seed with conical operculum (seed may be slightly reticulate but not longitudinally ribbed); some species variable and difficult to identify; angle of budding pouch and position of costa appear to be the most reliable characteristics; at least 10 spp. worldwide, especially warm temperate and tropical regions; diminutive of Wolffia, an apparent misnomer (according to W.T. Stearn, Botanical Latin, 1973, the suffix ella may be used without implication of smallness); Armstrong, W.P. (1992), Fremontia 20: 15-21; Landolt, E. (1984), Ber. Geobot. Inst. ETH, Stiftung Rubel 51: 164-172.

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