Wolffia arrhiza
Spotless watermeal
(c) Christian Fischer, some rights reserved (CC BY-SA) · licence
Family: Araceae · Type: Herb · Native
Wolffia arrhiza (Spotless watermeal) is a native California herb in the Araceae family, recognized by shape, pore count, and regional distribution.
Spotless watermeal is a native perennial found in San Diego County in freshwater habitats at elevations below 200 meters. Flowering from spring to summer, this tiny aquatic plant produces nearly invisible green flowers. Growing less than 1.5 millimeters in diameter, it forms small spherical bodies that float just beneath the water's surface with only the center slightly emerging. Its plant body is dark green with a flat upper surface and transparent base, featuring between 15 to 100 stomates. This diminutive watermeal is unique among aquatic plants for its incredibly small size, essentially vanishing into the water ecosystem.
Identification and appearance
Key characters: 3 sympatric species; distinguished by shape, pore count, and regional distribution
Habitat and range
Habitat: Uncommon. Freshwater
Elevation: < 200 m
Outside California: Europe, southwestern Asia, Africa
Bloom period
Wolffia arrhiza blooms Spring-summer.
How to tell it apart
vs Lemna: Wolffia is spherical and 0.4-1.3 mm; Lemna is disc-shaped, larger, and has a root.; vs Landoltia: Wolffia is spherical, rootless, and 0.4-1.3 mm; Landoltia has 2-7 roots and is much larger.; vs Spirodela: Wolffia is spherical, rootless, and 0.4-1.3 mm; Spirodela has 7-16 roots and is much larger.; vs Wolffiella: Wolffia is spherical like caviar; Wolffiella is flat and ribbon-shaped.
Frequently asked questions
Is Wolffia arrhiza native to California?
Yes. Wolffia arrhiza is native to California (recorded as native).
When does Wolffia arrhiza bloom?
Wolffia arrhiza blooms Spring-summer.
What plant family does Wolffia arrhiza belong to?
Wolffia arrhiza is in the Araceae family, genus Wolffia.
What habitat does Wolffia arrhiza grow in?
Wolffia arrhiza grows in Uncommon. Freshwater.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CalPhotos
Last updated 2026-10-07
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.