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Rare, native plant flourishes in Swan Creek Park

February 2, 2016


A delicate, flowering vine once believed to have vanished from the Washington landscape thrives in scattered patches along the Swan Creek canyon.

Torrey’s peavine, also known by the scientific name of Lathyrus torreyi, is one of Metro Parks’ little-recognized natural treasures.

This elusive plant, typically identifiable only from April through July, was first discovered in the woods near Swan Creek in the late 1990s by rare plant enthusiast Richard D. Van Deman, of Lakewood. At the time, Van Deman was active in the Washington Native Plant Society and found the peavine in bloom during a year-long plant survey he conducted in 1997 and 1998.

He’d seen the plant previously along a horse trail in what is now Joint Base Lewis-McChord, where it had been discovered in 1994. Before that, Van Deman’s attention was drawn to the plant during a lecture by a state native plant expert who said Torrey’s peavine no longer grew in Pierce County even though it was found historically here. “It was always in the back of my mind,” Van Deman said recently. “I just happened to stumble across it.”

Swan Creek Park is the northernmost site in the range of Torrey’s peavine, which also grows as far south as Santa Cruz, California, and is sometimes called the redwood pea. In Washington, it is officially listed as threatened with extinction. The U.S. Fish and Wildlife Service has identified Torrey’s peavine as a federal species of concern.

Relative to other vetches or wild members of the pea family, Torrey’s peavine is not particularly showy or aggressive. Lacking tendrils, Torrey’s peavine doesn’t climb; it typically hugs the ground. Unlike the luxurious blooms of other colorful vetches commonly seen along roadsides and elsewhere, Torrey’s peavine blossoms are few. Plants produce only one, two or -- at most -- three, dainty, blue-violet flowers in the spring. The blossoms don’t last long and the plants typically die back in mid-summer.

Perhaps one of the reasons Torrey’s peavine has persisted in Swan Creek Park is because the plant thrives along the edges of Douglas fir stands, where light filters through the tree canopy, said Mary Anderson, natural resources coordinator for Metro Parks. In some parts of the Swan Creek forest, trees have died – victims of laminated root rot, a fungal disease – and created openings that benefit the peavine’s spread, she said.

Torrey’s peavine may not dominate its surroundings, but it can carpet the ground if unmolested. So in the years since the rare plant was found in Swan Creek Park, native plant enthusiasts and park managers have guarded the plant’s habitat. For example, Anderson consults with Evergreen Mountain Bike Alliance volunteers to ensure that the bicycle trails that weave through Swan Creek’s 50-acre woodland do not disturb Torrey’s peavine.

Early on, conservation advocates recognized the menace posed by invasive species, which are non-native plants that crowd out others. Members of the Washington Native Plant Society, the Tahoma Audubon Society and others organized work parties to pull out English ivy, Scotch broom and Herb Robert, also known as geranium robertianum, a particular peril in shady areas.

If you’d like to volunteer to conserve Swan Creek’s natural areas, contact CHIP-in! Citizens Helping Improve Parks at chipin@tacomaparks.com, or Richard Madison, Metro Parks community outreach and special projects coordinator, at (253) 202-5978 or richardm@tacomaparks.com.

Learn more about Swan Creek Park.

Learn more about CHIP-in!