Azolla pinnataR. Brown

An aquatic weed often contaminating aquarium and nursery plants

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Name: Azolla pinnata R. Brown
Taxonomic Position:
Plantae*: Pteridophyta: Salviniaceae
Common Names: mosquito fern; ferny azolla (Australia); water velvet (Africa, N. America); aka-ukikusa (Japan)


Azolla pinnata is a Federal Noxious Weed commonly intercepted as a contaminant in aquatic plants for the aquarium and nursery trades. This attractive "fern" is often found being illegally propagated by unwitting hobbyists and in aquatic commerce.

Issues of Concern:

Azolla pinnata forms dense mats in waterways, which impede water flow, inhibit passage, and clog irrigation pumps. In addition to contaminating shipments, subsequent propagation by people unaware of its prohibited status represents a risk of establishment in the wild. This alga is capable of both vegatative and sexual reproduction. Azolla species are generally capable of doubling their biomass in 2 to 4 days.


Asia; Australasia; Africa

Quarantines: This alga is a U.S. Federal Noxious Weed

Detection Strategies

This plant is likely to be intercepted contaminating shipments of fish or aquatic plants. In addition, it may hitch-hike on agricultural equipment.


* Placed in Protista by some workers

Azolla pinnata grows in symbiosis with cyanobacteria (Anabaena), allowing it to grow in aquatic areas deficient in nitrogen.


Holm, L.G. (1997) World Weeds: Natural Histories and Distribution. Wiley Press, NY. pp 93-102

Useful Links:
Ferns of the Canberra Region (Good photos and descriptions)
Data sheet from New Guinea
Invaders Database
Another website (with photos)

Warning: The information in this archived item was not confirmed with the appropriate National Plant Protection Organization and is provided solely for informational purposes. Please use this information with caution.