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Common Name: Great Duckweed
Spirodela polyrrhiza is a Perennial up to 0.01 metres tall.
It has edible and medicinal uses.
Europe, including Britain, south and east from Scandanavia to N. Africa and Asia. America, Australia
Still water in ditches and ponds[
]. Eutrophic, quiet waters, in temperate to tropical regions[
Requires a sunny position in still water that is rich in nitrates and lime[
A very small plant without differentiation into various parts such as leaf, stem etc (they are called Thalli), it is 8mm in diameter and often forming a mat on the water surface and perennating by means of buds (turions) that sink in autumn and rise to the surface in spring. The so-called rootcap (really only an apical swelling), has a higher specific gravity than any other part of the plant, righting capsized individuals[
]. The plant rarely flowers, spreading mainly by vegetative means[
The plant is sometimes used as a food[
]. No more details are given.
The whole plant is antipruritic, antipyretic, cardiotonic, carminative, diaphoretic, diuretic[
]. It stimulates the appearance of measles rash[
]. It is used in the treatment of colds, measles, oedema and difficulty in urination[
The plant divides freely in the growing season and does not need help.