Undaria pinnatifida
Asian seaweed, Japanese kelp, wakame
(c) Javier, some rights reserved (CC BY), uploaded by Javier · licence
Family: Alariaceae · Type: Algae (Seaweed)
Conservation status: Cal-IPC Yes
Undaria pinnatifida (Asian seaweed) is a California algae (seaweed) in the Alariaceae family, recognized by Only Undaria in California (Channel Islands).
Asian seaweed is a non-native marine algae found in coastal marine environments along the Pacific Coast of California. Reproducing through spores and vegetative fragments from March to November, this brown seaweed forms distinctive fronds with a broad, feather-like pinnate structure up to 2 meters long. Growing as an invasive species, it attaches to hard substrates like rocky coastlines, pier pilings, and boat hulls using a holdfast root-like structure. Its complex blade has a midrib with deeply cut pinnate segments that create a delicate, feather-like appearance. The seaweed can rapidly colonize marine habitats, forming dense underwater forests that can displace native marine species.
Identification and appearance
Key characters: Only Undaria in California (Channel Islands)
Conservation status
Cal-IPC Yes
How to tell it apart
Differentiators are not available at this time.
Frequently asked questions
What plant family does Undaria pinnatifida belong to?
Undaria pinnatifida is in the Alariaceae family, genus Undaria.
Is Undaria pinnatifida invasive in California?
Undaria pinnatifida is listed by Cal-IPC with an invasiveness rating of Yes.
More California species
This species has no close relatives in our California data — here are other species to explore.
Last updated 2026-09-30
Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Cal-IPC, and more.