Selected Invasive Plants of Alaska

pocketguide cover image

On the cover: Bull Thistle photo taken by Michael Rasy, UAF Cooperative Extension Service

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Bull thistle forms dense, spiny, stands in meadows, pastures, streamsides, and forest openings. This highly-competitive weed monopolizes water, nutrients, and growing space. Once established, stands of bull thistle can suppress the growth of conifer seedlings, reduce land values, and restrict the movement of people and animals.

When trying to identify an unknown plant, color photos often help. This pocket guide provides a selection of invasive plants found across Alaska today. This booklet is not intended to take the place of more comprehensive reference guides, but to help those unfamiliar with these species to begin to recognize them, as the first step towards taking action.

  • In recent years, well established and expanding populations of highly invasive plants have been documented in Alaska.
  • These species pose a serious threat to Alaska's agriculture, tourism, wildlife, fisheries, and subsistence resources.
  • Alaska is in an unique position to avoid the extensive invasive plant problems that plague the rest of the U.S.

Photos provided by the USDA Forest Service State & Private Forestry or the UAF Cooperative Extension Service, unless otherwise noted.

List of Logo and Partnership of USDA Forest, UAF

Invasive plants in Alaska: Addressing this situation NOW will yield benefits for years to come.

Most introduced plant species are beneficial to Alaskans. We enjoy them in our gardens and they are agricultural staples.

However, a small subset of introduced plants is “invasive.” These non-native plants aggressively spread into places where they are not wanted.

People and vehicles generally spread invasive plants from human habitation centers outwards along transportation routes (roads, airports and float ponds, trails and rivers) as they move materials and goods.

Thank you for doing your part to insure that these invasive plant species, and others like them, do not spread into Alaska's wildlands.

This document was produced by:

Michael Shephard, USDA Forest Service, State & Private Forestry
Tom Huette, USDA Forest Service, State & Private Forestry
Jamie M. Nielsen, UAF Cooperative Extension Service
Charles Lindemuth, Chugach Design Group (pdf version)

[Image] Two images, Japanese knotweed near totem pole and community member working to control purple loosestrife in a city park

In Alaska we are concentrating on prevention, early detection, and rapid response.


Keeping these invasive plant species from becoming established in Alaska is the highest priority. This booklet is a tool to help identify some of the invasive plant species of greatest concern in Alaska.

Early Detection & Rapid Response:

Not only is it important to recognize these plants, but it is imperative that we find small infestations before they become too difficult to control.

The Alaska Soil and Water Conservation Districts, and many partner organizations, are in the process of forming “Cooperative Weed Management Areas” (CWMAs) across the state, to detect, monitor and treat invasive plant populations.

For additional information about invasive plants in Alaska:

Contact your local UAF Cooperative Extension Service office or appropriate local land management agency.

Or visit:

To view or contribute to the state-wide database of exotic plants and see the ranking of invasive plants in Alaska:

orange hawkweed on the Kenai NWR

Orange hawkweed invading the Kodiak National Wildlife Refuge.