The Tucson, Ariz.-based Center for Biological Diversity and the Utah Native Plant Society on Monday filed a federal complaint in Washington to force the Bush Administration to provide "critical habitat" for the Holmgren milkvetch and the Shivwits milkvetch - a pair of nearly extinct wildflowers found only in the Mojave Desert near the Utah-Arizona border.

The two plant species are in the path of a planned freeway interchange and roadway in St. George's south corridor that would link the city with its proposed new airport and a planned community.

"These lawsuits don't happen for no reason," said Daniel Patterson, an ecologist with the Center for Biological Diversity. "We gave over two months notice and still didn't get a response. It leaves citizens with little choice but to move in to the courts to ensure that endangered species are protected and recovered."

The two plant species were placed on the endangered list in September 2001 by the Interior Department's Fish and Wildlife Service, which is charged with recovering plant and animal species under the Endangered Species Act. But the FWS has never designated any critical habitat - areas where humans should tread lightly or not at all - for the plants.

A call to a spokeswoman with the Department of Interior's Fish and Wildlife Service was not returned Monday. Earlier this year, however, an FWS official said that the species weren't high enough on the agency's priority list to receive critical habitat dollars.

That's a violation of the law, according to Tony Frates, rare plant coordinator with the Utah Native Plant Society.

"Both of these species were listed with the critical habitat designation, but nothing has been done, and now there's a lot of stuff going on now in that area, an extreme amount of planning," he said. "Both species are threatened, but the Holmgren milkvetch is particularly threatened because it's in such terrible shape."

Frates says the value of preserving the two plant species may not be readily apparent. "But they are a piece of the larger ecosystem, a community of plants and animals that depends on each other. And when you lose them it starts a domino effect. We can't separate the natural world from our own existence."

Patterson says the lawsuit is not aimed at the proposed freeway project.

Rather, he said, it is "to obtain critical habitat for these plant species. Anywhere the freeway is located is where urban sprawl is going to occur. That's why they need to get these critical habitats in place, before the growth occurs and it's too late."

jbaird@sltrib.com