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Spirodela polyrhiza (L.) Schleid.

Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

Spirodela Schleid. (ウキクサ)

Aquatic plants
S. oligorrhiza (Kurz) Hegelm. (ヒメウキクサ), Africa, Australia, southern Asia (exotic to Japan)
S. polyrrhiza (L.) Schleid.
S. punctata (G. Mey.) C. H. Thomps., South America, Central America, West Indies (syn. Landoltia punctata (G. Mey) Les et D. J. Crawford), dotted duckweed
S. sichuanensis M. G. Liu et K. M. Xie, southern China

Spirodela polyrhiza in Hokkaido

Ukikusa (ウキクサ, 浮草), great duckweed
Lifeform: annual aquatic forb
Distribution: cosmopolitan between tropical and temperate regions
Habitat: stagnant water, e.g., ponds and paddy fields
Leaf: face = green, reverse = red-brown
Root: 5-12 per thallus
Reproduction: mostly depending on vegetative reproduction, developing dormant buds by winter
Genome: analysis completed in 2014

[1-3] at a small artificial pond in the Sapporo City Nature Education Park on September 19 2016. The small leaves are Lemna minor.