Description: Small herbs, floating on or near surface of the water, or completely submerged, monoecious, solitary or in groups, each consisting of a ± globose or flat and leaf-like green plant body undifferentiated into stem and leaves (a thallus); roots absent or 1–several. Reproduction is usually vegetative by new leaf-like thalli emerging from a small slit or budding pouch; pouches usually 2, 1 on each margin or sometimes 1 marginal and the other on the upper surface; the young thalli remaining attached to the 'parent' thallus for some time.
Inflorescence of 1 female and 1 or 2 male flowers in 1 of the marginal pouches , or in the pouch on the upper surface. Flowers very rare, unisexual. Perianth absent. Male flowers with 1 or 2 stamens; anther 2- or 1-locular, dehiscing by longitudinal or transverse slits. Female flowers with a 1-locular superior ovary; ovules 1–7, style short, unbranched.
Fruit a small 1–4-seeded utricle.
Distribution and occurrence: World: 6 genera, c. 40 species, cosmopolitan. Australia: 3 genera, 10 species, all States.
Angiosperm Phylogeny Website (Family: Araceae, Order: Alismatales)
The characters used in this classification of this family include the plants' responses to artificially manipulated environmental conditions. The range of these responses far exceeds the observable morphological variations. Therefore, the species of this family are difficult to identify. Several specimens in a population should be examined; the diagnostic features are easier to observe in fresh material.
Text by B. J. Conn
| ||Key to the genera|| |
|1||Roots absent and thallus more or less globose, ellipsoid or ovoid||Wolffia|
|Roots present and thallus more or less flattened (roots mostly absent in Lemna trisulca)||2|
|2||Roots 1 per thallus, rarely none; thallus with 1–5, often indistinct veins||Lemna|
|Roots 1–18; thallus with 3–15, often indistinct veins|
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