The term "exotic plant" conjures up images of tropical flowers or jungle vines. But dandelions?

There are four species of dandelion in the Yukon, says Bruce Bennett of the Canadian Wildlife Service in Whitehorse, and two of them are exotics. In biologist's terms, that means they have been introduced from other areas.

It's difficult to tell exactly how many species of Yukon plants should be classified as exotics because so little is known about native Yukon plants. Bulrushes, for example, are considered an introduced species in the Yukon, but they might be native, Bennett says.

On the other hand, clover is definitely exotic. "Every species of clover we have in the Yukon is introduced," says Bennett.

The largest group of introduced plants is the grasses. Thirty-nine non-native grass species have been recorded in the Yukon, including oats, wheat, and other grains that have escaped cultivation and now grow wild.

The next largest group is the asters, including the two introduced dandelions. They are generally tough, weedy plants that grow wherever the seeds fall.

The Yukon also has 16 introduced species of borages, a group of agricultural weeds that includes stickseeds and forget-me-nots, and 14 introduced species of mustards.

Many of the exotics are associated with agriculture, Bennett says. They enter the territory in bales of hay, as burrs attached to the coats of animals, or mixed in with seed. Some are introduced deliberately as crops or, like the pea family, to improve and stabilize soil.

Others arrive on travelers -- human, animal, and mechanical. The weed that got caught in your car's bumper around Dawson Creek might drop its seeds when you stop to take photographs near Dawson City, and the Yukon will have another exotic species.

Exotics are not necessarily a problem, Bennett says. Most are annuals, which tend not to do well in the Yukon because of the poor soil and harsh climate. Some are even beneficial, at least to some Yukoners. The clovers are a popular food among bears, and redpolls and juncos feast on lamb's quarters, which is widespread in the Whitehorse area.

"We have nothing like broom that takes over everything," says Bennett. However, a few noxious exotics have been found in the territory, including Canada thistle and knapweed.

Although knapweed is a serious problem in southern Canada, Bennett says, it was reported in the Yukon for the first time only a few months ago when a patch of knapweed was identified in Haines Junction. The man who reported it pulled up the patch of weed and destroyed it. It's important to catch knapweed before it goes to seed, says Bennett.

"Its seed can remain viable in the soil for at least 10 years, and maybe longer."

Like most exotics, the knapweed probably accompanied a human traveler to the Yukon as an unnoticed hitchhiker. Exotics generally grow where the human traffic is heaviest. If the human traffic drops off, the tough northern plants tend to take back their territory.

"They found in Churchill, Manitoba, that once people leave, so do the weeds," says Bennett.

Estimates place the proportion of introduced species in the Yukon at about 13 percent of reported Yukon flora, well below the Canadian average of 27 percent.

"However, that may be because we haven't looked for them," Bennett says. "They're often considered weeds, and there's very little known about weeds in the Yukon because people don't collect them."

Bennett identified three previously unreported exotics in a Whitehorse subdivision last fall while shopping at a yard sale, and he suspects there are many more to be found.

"If anybody wants to give me some weeds, I'll be happy to identify them," he says.

For more information on exotics in the Yukon, contact the Canadian Wildlife Service, Environment Canada, in Whitehorse.