yukons flora continues to grow

Finding a new plant species requires the detective skills of a Sherlock Holmes - time, patience, and cunning. That's why Yukon biologist Bruce Bennett was excited.

by Patricia Robertson

Finding a new plant species requires the detective skills of a Sherlock Holmes – time, patience, and cunning. That’s why Yukon biologist Bruce Bennett was excited when, for the second time in his life, he was instrumental in confirming the existence of a new species of plant in North America. Not only that, but this species, a Russian native called Siberian cow parsnip (Heracleum sibiricum), was previously unknown in North America.

The story begins in the summer of 1991, when Greg Brunner of Dawson City collected a plant he identified as wild parsnip (Pastinaca sativa) near Henderson Corner, on the Klondike Highway. Wild parsnip was known to have been cultivated at one time in west Dawson, and Brunner’s find was confirmed by Bill Cody, who wrote Flora of the Yukon Territory.

“Greg showed it to me and I made a collection in 2005,” says Bennett. “Then in 2007 I got a collection from a friend in Ontario of wild parsnip, and it was a totally different plant. So immediately I knew what I had wasn’t wild parsnip, but I didn’t know what it was.”

Bennett contacted a herbarium in Ottawa, which identified it as cow parsnip (Heracleum maximum). Cow parsnip is the only Yukon member of the genus Heracleum, so named after the Greek demigod Hercules (noted for his size and strength) because of the very large size of the plant’s parts. Its juices contain a phototoxin that can cause anything from a mild rash to severe blisters.

The plant Bennett was trying to identify indeed resembles cow parsnip, except that it has a very distinctive leaf shape. “I didn’t believe it was cow parsnip,” Bennett says. “I thought it came from Siberia.” He checked the Russian plant collections at the Royal BC Museum in Victoria and the University of Alaska Fairbanks, without success.

Eventually, through his work as a reviewer for the multi-volume Flora of North America, Bennett heard of a botanist in North Carolina, Derick Poindexter of Appalachian State University, who was working on the cow parsnip group. “I sent him a photo and he immediately said, ‘I think what you’ve got is Siberian cow parsnip (Heracleum sibiricum).’”

So it turns out that Bennett’s theory about the plant’s origins were correct. But why did he think it was Siberian in the first place? “Most of the plants in the Dawson region have a Russian affinity, and many introduced plants, including May tree and caragana, have their origins in Russia.”

Bennett had also seen photos of the Siberian carrot family that resembled the unidentified plant. “But Siberian cow parsnip has many different leaf forms – it can even have different leaf forms on the same plant – so that’s why it’s a tricky one to identify.”

How did the plant get to Henderson Corner? (It’s also been found in at least three other sites in Dawson, including disturbed sites in the Bear Creek area.) “That’s what we hope the publication of this column will answer,” says Bennett. “If someone sees the photo, they may be able to tell us where it came from. It may just be a horticultural escape; we don’t know.”

Bennett sent an email with photos to all the botanists in Alaska, but so far no one has confirmed its existence there. “As far as we know, this is the only place it occurs in North America. So it’s a first for this continent.” It’s likely the plant was intentionally planted as a horticultural item or came in as an agricultural byproduct, given where it’s found growing, says Bennett. “But if this particular plant population didn’t come from somewhere else in North America, it had to come from Russia, so there must be an interesting story there.”

Siberian cow parsnip isn’t the only new plant added to Yukon’s flora this fall. A new species of Jacob’s ladder, found only in the mountainous areas of Yukon and Alaska that escaped glaciation during the last ice age, has been confirmed as well.

Jacob’s ladder is a species of flowering plant in the phlox family. Of the three species in the Yukon, tall Jacob’s ladder (Polemonium acutiflorum) grows in both low and high elevations, while showy Jacob’s ladder (Polemonium pulcherrimum) is only found in low-lying areas. The third species, northern Jacob’s ladder (Polemonium boreale), grows in the mountains around the circumpolar North.

But two botanists working on Arctic flora – Reidar Elven at the University of Oslo and David Murray at the University of Alaska Fairbanks – noticed that some of the northern Jacob’s ladder plants were a little different. The heads of these plants are covered with long brownish hairs and the flowers don’t open as widely.

“People originally thought that these were the same plant growing in different habitats,” says Bennett. But now these hairier versions of northern Jacob’s ladder have been established as a separate species, named Polemonium villosissimum.

Not only that, but the new species is unique to our area. “They’re genetically different and have different pollination schemes,” explains Bennett. “It’s an overlooked plant that grows only in the high alpine of southwest Yukon and southeast Alaska.”

Bennett checked his own herbarium and discovered that he actually had one specimen of the new species. “There’s a lot of variation in the way these plants grow, so you have to decide what is variation and what is a distinctive species,” says Bennett. “For a plant to be a distinct species, you have to have either genetic difference or else a different flower structure so that the plant can’t cross-pollinate with other members of that plant family.

“That’s what we found here. The way the anthers, or the pollen carriers at the tips of the stamens, are positioned, means that Polemonium villosissimum can’t cross-pollinate with Polemonium boreale.”

Elementary, my dear Watson.

This column is co-ordinated by the Northern Research Institute at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.

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