Spirodela

Spirodela is a genus of aquatic plants, one of several genera containing plants commonly called duckweed. Spirodela species are members of the Araceae under the APG II system. They were formerly members of the Lemnaceae.

Description
Spirodela species are free-floating plants that have their stem transformed into leaf-like structures called fronds; each plant is represented by a frond with roots, therefore they do not have leaves. Two to five plants may remain connected to each other.

Plants are green, but may turn red due to the presence of anthocyanin. Multiple roots (5 to 20, depending on the species) emerge from each frond. Spirodela is larger (10 mm) than Lemna (2 mm – 5 mm, with one root per frond).

Certain species of Spirodela overwinter as turions, dormant starchy shoots that lack air pockets, which sink to the bottom of the water. In spring, turions rise to the surface and germinate.

Spirodela often forms floating mats with related species (e.g. Lemna and Wolffia).

The genus is virtually cosmopolitan in distribution.

Species
There are currently 2 recognized species in this genus:
 * 1) Spirodela polyrhiza (L.) Schleid. - cosmopolitan
 * 2) Spirodela intermedia W.Koch