DENVER (AP) – Seven conservation groups are planning to sue the U.S. Fish and Wildlife Service for keeping two rare species of desert flowers off the federal list of endangered species.

The Center for Biological Diversity says the groups filed a formal notice of intent Tuesday to sue over the status of White River and Graham’s beardtongues. Environmentalists have been trying for decades to win Endangered Species Act protection for the species of penstemon, which are known to grow only on oil shale outcroppings in Utah’s Uinta Basin.

The Fish and Wildlife Service formally proposed listing of the plants in August 2013. But the agency then issued a draft conservation agreement it said would better protect the plants without the economic consequences a listing could have for oil exploration in northeast Utah and northwest Colorado.

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