Phil Caswell had been looking for Draba yukonensis for four years without success.

Draba yukonensis is extremely rare and, at barely 15 cm tall, easy to overlook. (photo: Gerry Mussgnug)

The amateur botanist from New York began coming to the Yukon in 2000, to look for plants on behalf of Kluane National Park and Preserve. He especially wanted to find the rarest plant in Canada -- a small member of the mustard family called Draba yukonensis, or Yukon Whitlow-grass.

"It was a quest of his," says Bruce Bennett, botanist with NatureServe Yukon in Whitehorse.

Draba yukonensis was a worthy quest. The tiny, inconspicuous plant had been seen and collected only three times, always from a specific area along the Alaska Highway in the Kluane region.

In 1944, botanist Hugh Raup and his wife spotted the little plant, noted its location, and added a specimen to Raup's extensive collection of northern plants.

In 1957, eminent Vancouver botanist Wilf Schofield and his colleague, H.A. Crum, found the plant just outside their tents. From Schofield's description of the site, Bennett suspects he was camping in the same place Raup and his wife had chosen in 1944.

Now two specimens of the rare plant existed, in two different collections, but no one had identified it as a new species.

In the early 1970s, National Museum of Canada chief botanist Erling Porsild was reviewing Draba collections and realized that the tiny plant collected twice from beside the Alaska Highway was not quite like anything else in the collections. He published a formal scientific description in 1975, naming the plant Draba yukonensis.

Not long after the description was published, says Bennett, another example of the plant was found in a collection made in 1973 from the same Alaska Highway location, but that was the end of the sightings for decades.

The Yukon still had Drabas -- at least 30 species. Draba from the Rocky Mountains and Beringia grow in the Yukon, along with a few species called "endemic" because they are found nowhere else.

"This is the Draba capital of the world," says Bennett. "Alaska has three more species, but it's also three times the size."

But no one could find Draba yukonensis. In a 2005 publication on Canadian species of global conservation concern, the little plant was listed as Historic.

"There was a dedicated effort for four years to find this, and it hadn't shown up. So that's why we listed it as Historic," says Bennett. "Historic means extinct with hope."

Hope, however, was wearing thin until the day last spring when Phil Caswell took Kluane park warden Lloyd Freese out along the Alaska Highway to show him where to look for Draba yukonensis and how to identify it.

As Bennett tells the story, Caswell was explaining that the mysterious plant would look similar to another nearby species of Draba.

"Lloyd grabbed one and said, 'Like this?' And before he knew it he had three Draba yukonensis in his hand," Bennett says.

By coincidence, just as Caswell and Freese were rediscovering Draba yukonensis, Bennett was e-mailing them a description of the location where Wilf Schofield had found the plant 50 years earlier. It was the same place.

Caswell and Bennett were sure they'd found the missing plant, but they needed confirmation. The plants didn't quite fit the formal species description published in 1975. Bennett thought that might be because the description was based on such a small number of samples.

"If you've only seen the back end of an elephant, you might not realize it has tusks," he explains.

To confirm the identification, Bennett went to Ottawa and consulted with Gerry Mulligan, Canada's mustard specialist. They concluded that it could be nothing else -- the lost plant had been found.

Unfortunately, its survival is far from assured. Caswell and Freese found 18 plants. When Bennett and a photographer went out a week or so later to take the first photographs of the species in the wild, only 8 plants remained. Not long after that, a researcher hoping to collect seeds from the plants at Bennett's request could not find a single plant.

"All the plants were gone. Arctic ground squirrels, we believe," says Bennett.

He hopes that the plants will come back in the spring, and he'll be out there looking for them before the ground squirrels start grazing on them. But the single known stand of Draba yukonensis is vulnerable to other threats as well. It's located outside the bounds of Kluane National Park, next to a busy highway.

"Most people don't realize that the rarest plant in Canada is in the Yukon, and it's under threat of extinction," Bennett says. "It would be very easy to take a grader and eliminate the known population -- completely unintentionally."

Sadly, Phil Caswell, whose quest led to the rediscovery the little plant, passed away in October 2005 after devoting many years to botany in the Yukon and Alaska.

"His dedicated efforts will be remembered," Bennett says.

For more information about Draba yukonensis and other rare Yukon species, contact Bruce Bennett at NatureServe Yukon, (867) 667-5331.