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NATURAL HISTORY

COOK’S LOMATIUM } Lomatium cookii
FAMILY: Apiaceae

DESCRIPTION: The Cook's lomatium is a small, perennial plant in the parsley family that grows to be up to 1.6 feet tall. It has a slender, twisted taproot, which often branches at ground level, forming multiple stems. Leaves are smooth, finely dissected, and strictly basal. An umbel of pale yellow flowers develops boat-shaped fruits eight to 13 millimeters long. In years of good rainfall, Cook’s lomatium plants put up aboveground growth and then die back to their underground stems during the summer, fall, and winter, only to rise again when water is present. If rain is scant, the plants may not even put up aboveground growth, making them impossible to see.

HABITAT: This plant occurs only where soil types have a hard pan or clay pan layer close to the soil surface, creating seasonally wet soils and vernal pools. The Agate Desert is characterized by shallow, Agate-Winlow soils, a relative lack of trees, sparse prairie vegetation, and agate on the soil surface. Associated species in the Agate Desert include meadowfoams, Plagiobothrys bracteatus, and navarretia. Associated species at French Flat include California oatgrass, Plagiobothrys bracteatus, shaggy horkelia, the short-stemmed star tulip, and sedge-leaf buckbrush.

RANGE: This species is known from the Agate Desert near Medford, Jackson County, Oregon and French Flat in the Illinois Valley in Josephine County, Oregon.

LIFE CYCLE: Flowering usually occurs from mid-March through mid-May. The typical lifespan of the plant is currently unknown and unstudied.

THREATS: The Cook’s lomatium has declined because of industrial, commercial, and residential development; road and power-line construction and maintenance; hydrological alteration; livestock grazing; agricultural conversion; weed competition; mowing; and roadside spraying. In Josephine County, Cook's lomatium is also threatened by gold mining, logging, fire suppression, and uncontrolled off-road vehicle use.

POPULATION TREND: By 2002, while some populations had shown local increases in abundance, the plant’s overall Agate Desert range had declined by roughly 50 percent. As of 2006, the Cook’s lomatium was reduced to 13 populations and about 34,000 total plants in the Agate Desert. About 24 populations were still found in the French Flat area.

Photo © Ian Silvernail, Oregon Department of Agriculture