Dudley Bluffs Twinpod

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Dudley Bluffs Twinpod

Physaria obcordata

ListedFebruary 6, 1990
FamilyCruciferae (Brassicaceae)
DescriptionLow-growing perennial with hairy leaves and yellow, four-petaled flowers.
HabitatOil shale outcrops.


The Physaria obcordata (Dudley Bluffs twinpod) is a low-growing perennial in the mustard family that reaches a height of 4.8-7.2 in (12-18 cm). The hairy leaves, which are oblanceolate and untoothed, appear silvery. Plants bear small, yellow, four-petaled flowers and heart shaped fruits.


Found only in the Piceance Basin of Colorado, Dudley Bluffs twinpod grows on the slopes of barren, white oil shale outcrops. It is often found near another Threatened mustard, the Dudley Bluff bladderpod (Lesquerella congesta), which grows on level shale outcrops. The species occurs at elevations of from 5,960-7,440 ft (1,806-2,255 m). The surrounding hills and mesas support pinyon-juniper woodlands.


Dudley Bluffs twinpod was discovered in 1982 in Rio Blanco County, northwestern Colorado, during a survey of the flora of the Piceance Basin conducted by the state Natural Heritage Inventory for the Bureau of Land Management (BLM). The species has not been found outside this basin.

This twinpod is currently found at five sites in Rio Blanco County, mostly on federal land administered by BLM. There are three known populations along Piceance and Yellow creeks and two populations on Calamity Ridge. These five populations cover approximately 250 acres (101 hectares) over a 15 mi (24 km) range. The largest population, consisting of about 10,000 plants, is on BLM land at the junction of Piceance Creek and Ryan Gulch. This site also supports a similar number of the Dudley Bluffs bladderpod (Lesquerella obcordata). At the Dudley Bluffs site the species occurs on both BLM land and private land.


The main threat to the Dudley Bluffs twinpod is the mining of its habitat for rich deposits of oil shale and sodium minerals, such as nahcolite and dawsonite. While mining is not imminent, long term mining plans are clearly a threat to the species. As the federal government seeks alternative energy sources to imported petroleum, subsidy programs for oil shale development continue to be proposed in the U.S. Congress.

Yellow Creek, Dudley Bluffs, and Ryan Gulch are on oil shale deposits which could be mined by open-pit methods. A pilot project for an underground nahcolite solution mine has been established between Piceance Creek and Yellow Creek, and a commercial mine has been proposed for the area which would cover 254 acres (102 hectares). These activities could result in the destruction or modification of almost three-quarters of the entire Dudley Bluffs twinpod habitat. BLM has decided not to lease the commercial mineral rights to the area until improved mining technology is developed, but is still considering leases for noncommercial research purposes. While BLM has designated the federal portion of the Dudley Bluffs site and one of the Calamity ridge sites as "areas of critical environmental concern,' this protects only about 250 acres (101 hectares) of twinpod habitat.

Although Dudley Bluffs twinpod is locally abundant in its specialized habitat, its extremely limited range makes it vulnerable to surface disturbance. The Rio Blanco County government, as well as oil shale and nahcolite companies opposed the listing of Dudley Bluffs twinpod as a Threatened species.

Conservation and Recovery

The Fish and Wildlife Service published a Recovery Plan for the Dudley Bluffs twinpod in 1993. Most of its critical habitat is owned by the Bureau of Land Management (BLM), a federal agency. The BLM has designated a section of Dudley Bluffs as an "Area of Critical Environmental Concern," which gives protection to about 50 acres (20 hectares) of critical habitat. Other critical habitat is owned by the Colorado Division of Wildlife. Additional areas of these publicly owned habitats should be protected from threatening activities. Some critical habitat is on private land and should also be protected, either by acquisition and designation as ecological reserves, or by the negotiation of conservation easements with the owner. The populations of the Dudley Bluffs twinpod should be monitored, and research undertaken into its biology, habitat needs, and beneficial management practices.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
P.O. Box 25486
Denver Federal Center
Denver, Colorado 80225


Bureau of Land Management. 1987. "Piceance Basin Resource Management Plan Record of Decision." U.S. Government Printing Office, Washington, DC.

Colorado Native Plant Society. 1989. Rare Plants of Colorado. Colorado Native Plant Society and the Rocky Mountain Nature Association, Estes Park, Colorado.

Colorado Natural Areas Program. 1987. "Status Report for Physaria obcordata." Denver, Colorado.

U.S. Fish and Wildlife Service. 1993. "Dudley Bluffs Bladderpod and Dudley Bluffs Twinpod Recovery Plan." Denver, Colorado.