Azolla microphylla
Mexican mosquito fern
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Family: Azollaceae · Type: Herb · Native
Conservation status: CNPS 4.2
Azolla microphylla (Mexican mosquito fern) is a native California herb in the Azollaceae family.
Mexican mosquito fern is a California native aquatic fern found in northern Sierra Nevada, Great Valley, Central Coast, San Francisco Bay, San Bernardan, and northeastern Sierra Nevada regions in ponds and slow streams at elevations below 1,200 meters. Its color ranges from green to blue-green and can turn dark red, with distinctive tiny surface papillae on its upper leaf lobes. Growing prostrate with stems generally 1 to 1.3 centimeters long and extremely short internodes less than 1 millimeter, this tiny fern creates delicate mat-like formations in quiet water environments. Its leaves feature conspicuous papillae on the upper surface, giving the plant a textured, almost fuzzy appearance. The plant develops both male and female sporangium cases, often with an equatorial girdle and a surface that ranges from smooth to subtly pitted.
Identification and appearance
Key characters: 1 sympatric species. Key differentiator is conspicuous vs. inconspicuous papillae and prostrate habit.
Habitat and range
Habitat: Ponds, slow streams
Elevation: < 1200 m
Outside California: to British Columbia, central United States, South America
Conservation status
CNPS 4.2
How to tell it apart
vs Lemna: Lemna has smooth round pads; Azolla has branching stems with minute scale-like leaves.; vs Spirodela: Spirodela has flat green fronds; Azolla has tiny overlapping scales creating fuzzy texture.; vs Eichhornia: Eichhornia has large inflated leaf stalks; Azolla is minuscule at under 3 cm.; vs Pistia: Pistia forms 10+ cm rosettes; Azolla is tiny at under 3 cm with branching stems.; vs Salvinia: Salvinia leaves are fingernail-sized (5+ mm); Azolla leaves are pinhead-sized (under 2 mm).
Frequently asked questions
Is Azolla microphylla native to California?
Yes. Azolla microphylla is native to California (recorded as native).
What plant family does Azolla microphylla belong to?
Azolla microphylla is in the Azollaceae family, genus Azolla.
Is Azolla microphylla rare or endangered?
Azolla microphylla carries California Rare Plant Rank 4.2, state rank S4.
What habitat does Azolla microphylla grow in?
Azolla microphylla grows in Ponds, slow streams.
Related species
Other California species in the same genus, family, or bioregion.
Sources: Jepson eFlora · CNPS Rare Plant Inventory · Index of California Plant Names · CalPhotos · CDFW CNDDB
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.