The Center for Biological Diversity and Utah Native Plant Society sued the federal agency in September, demanding it designate critical habitat to protect the Holmgren milkvetch and Shivwits milkvetch, which grow almost exclusively near St. George.

Tony Frates, a rare-plant coordinator with the Utah Native Plant Society, said both wildflowers are severely threatened by increasing development.

The Fish and Wildlife Service added the plants to the endangered species list in 2001, but no critical habitat was designated.

Such a designation would not necessarily close the land to development, but it would require consultation with the agency and possible remediation if a housing development or new road harmed the plants' habitat.

The Fish and Wildlife Service has agreed to propose critical habitat by March 17, 2006, and to finalize a proposal by Dec. 16 of that year.

There are three areas where the Holmgren milkvetch grows. One is in the path of a planned Interstate 15 freeway interchange and road in St. George's southern corridor as well as a planned community.

Washington County Commissioner Alan Gardner said steps have been taken to protect the plants. The Nature Conservancy plans to buy some state-owned land where the plants are growing for conservation. Other areas are far from development, he said.

Both desert plants grow in rocky soil and are part of the pea family.

The Holmgren milkvetch grows closer to the ground and has white-tipped purple flowers.

The Shivwits milkvetch is taller, bushier and has yellow flowers.

Daniel Patterson, desert ecologist with the Center for Biological Diversity, said, "As wildlife habitat in the Mojave Desert is lost, so is the human quality of life.

"We offer to work closely with [the Fish and Wildlife Service] to get a proposal done quickly to secure habitat for conservation and recovery.

"Too bad it took a lawsuit to get [the agency] to move."

Even if the federal government designates areas as critical habitat, many of the areas where the plant grows are actually on state land, Frates said.

"It still doesn't force the state of Utah to do a single darn thing on their land unless they apply for federal funding for a highway or something," he said.

The designation would make the state aware that the plants should be taken into account when planning development, he added.