Description: Herb floating at water surface, solitary or thalli connected to form groups of 2–5 (or more); roots 5–18 per thallus. Thallus symmetric or asymmetric, elliptic to obovate (broad-ovate, oblong-elliptic or slightly reniform), flat, length to breadth ratio 1–1.5, above yellow-green, lower surface usually with red or purple tinge; veins c. 7–16; dorsal and ventral scale present. Budding pouch with slit on the lower surface to the margin of the thallus.
Inflorescence of 1 female and 2 male flowers together in a membranous bract. Anther 2-locular.
Distribution and occurrence: World: 3 species, temperate & tropical regions. Australia: 1 species; WA (naturalised), NT, Qld, NSW, Vic.
The dorsal scale is present on young thalli, but not persistent in older plants. The ventral scale, which is often pigmented, covers the bases of the secondary roots or is united with the root sheaths of the primary roots. Spirodela was formerly placed in Lemnaceae.
Text by (adapted from) B.J. Conn, Flora of New South Wales Vol. 4 (1993)
Taxon concept: Australian Plant Census (accessed May 2017)
|One species in NSW: Spirodela polyrhiza|