Spirodela is a small genus of free-floating aquatic plants belonging to the family Araceae (order Alismatales). Together with the closely related genera Lemna, Wolffia, and Landoltia, its members are collectively known as duckweeds — among the smallest and simplest flowering plants on Earth. The genus was formerly placed in the family Lemnaceae, which is now subsumed within Araceae under the APG classification system.
Plants in Spirodela lack conventional leaves and stems. Instead, the plant body is reduced to a flattened, leaf-like structure called a frond, typically around 10 mm across — noticeably larger than Lemna fronds, which range from 2–5 mm. Each frond bears multiple roots (between 5 and 20 depending on species), a key distinguishing feature from Lemna, which has only a single root per frond. Between two and five fronds may remain connected, forming small colonies on the water surface.
Fronds are typically green but may take on a reddish hue due to anthocyanin pigmentation. Certain species produce turions — dormant, starch-filled, root-free bodies that sink to the bottom of ponds or lakes during cold months and rise to the surface in spring to germinate, enabling the plant to survive winter conditions in temperate climates.
Spirodela is cosmopolitan, occurring on every inhabited continent. It frequently forms dense floating mats alongside related duckweed genera such as Lemna and Wolffia. As of late 2025, Plants of the World Online recognises four accepted species in the genus: S. polyrhiza, S. punctata, S. oligorrhiza, and S. sichuanensis.
Distribution
Spirodela has a cosmopolitan distribution, occurring on every inhabited continent in still or slow-moving freshwater habitats such as ponds, lakes, and ditches. It frequently co-occurs with other duckweed genera including Lemna and Wolffia.
Ecology
Spirodela species are free-floating aquatic plants that form dense surface mats in calm freshwater. Some species produce turions — dense, starchy, dormant propagules that sink to the bottom in autumn and overwinter there, rising and germinating in spring when temperatures warm. These plants often grow together with Lemna and Wolffia, collectively covering water surfaces and influencing light penetration and nutrient dynamics in their habitats.
Taxonomy Notes
Spirodela was traditionally placed in the family Lemnaceae alongside the other duckweed genera. Under the APG II (and subsequent APG) classification systems, Lemnaceae has been sunk into Araceae, so Spirodela is now classified within that family, in the order Alismatales. The genus is distinguished from Lemna primarily by its larger frond size and multiple roots per frond (5–20 versus one in Lemna).
