There are aliens among us and they’re reproducing at an alarming rate.

The exotic weed Cirsium palustre, better known as marsh plume thistle, is rapidly invading B.C.’s north between McBride and Prince George. With no known natural enemies to control it, marsh plume thistle threatens to occupy sites that would otherwise support a diversity of native plant species.

The consequences can be serious: These weeds degrade animal habitat and forage, reduce biodiversity, choke out riparian areas and impede the growth of desired plants.

Marsh plume thistle was first documented in Prince Rupert in 1954. It was likely introduced to the McBride area within the last 15 years.

"It can flourish in a variety of sites. We have even found it growing under forest canopy," said UNBC co-op student Kristin Maitland, working for the Prince George forest region.

This thistle is conspicuous once it reaches the stem- and flower-bearing reproductive phase. It grows to about 1.5 meters, with a distinctively unbranched, narrow stem. In the fall, each flower produces numerous, wind-dispersed seeds, which can persist in the seed bank for several years

Destroying the weed remains a puzzle. "We can’t use chemicals in riparian areas," said Perry Grilz, Range Planner with the Prince George forest region. "We are trying to devise a containment program that will stop it from spreading beyond its current range."

If you discover this plant growing beyond its known range, please call Perry at (250) 565-6774.

Editor’s Note: The Marsh Plume Thistle is classed currently in B.C. as a nuisance, rather than noxious, weed. The ministry is part of an international program working to cut populations of unwanted weeds to levels that are ecologically and economically acceptable. The program’s tools include prevention, herbicide spraying, hand-pulling, seeding, clipping and biological control—the use of parasites, predators and pathogens to attack unwanted species.

The marsh plume thistle is just one of the many problematic weeds that grow in B.C.

This Ministry of Agriculture Web site lists B.C.’s noxious weeds and provides photos of each: http://www.agf.gov.bc.ca/croplive/cropprot/weedguid/weedguid.htm

The Ministry of Forests offers a list of insects that attack problem weeds at: http://www.for.gov.bc.ca/hfp/pubs/interest/bioagent/bioagent.htm

The two ministries together published a handy, pocket-sized Field Guide to Noxious and Other Selected Weeds, updated this year and available through forest district and regional offices. If the local supply is low, offices can order more from the Forest Practices Branch in Victoria.