Eriogonum umbellatum

Eriogonum umbellatum is a species of wild buckwheat known by the common name sulphurflower buckwheat, or simply sulphur flower.

Description
It is an extremely variable plant and hard to identify because individuals can look very different from one another. Also, there are many varieties. It may be a perennial herb blooming by summer with stems 10 cm tall and two to six clusters of flowers, with a whorl of leaves below the stems, or a sprawling shrub approaching 2 m high and wide. The leaves are usually woolly and low on the plant, and the flowers come in many colors from white to bright yellow to purple.

Varieties

 * E. u. var. argus - often nearly hairless leaves and bright yellow flowers; limited to the Klamath Mountains
 * E. u. var. dichrocephalum - found throughout much of the western United States
 * E. u. var. furcosum - a low shrub native to the Sierra Nevada
 * E. u. var. glaberrimum - (green buckwheat) - a nearly hairless, white-flowered species
 * E. u. var. humistratum - (Mt. Eddy buckwheat) - a rare northern California endemic
 * E. u. var. juniporinum - (juniper buckwheat) - an uncommon plant of eastern California and western Nevada
 * E. u. var. subalpinum - (sulfur buckwheat) - similar to Eriogonum eriogonum but has wider and more spoon-shaped leaves
 * E. u. var. torreyanum - (Donner Pass buckwheat) - known from fewer than 10 occurrences near the Donner Pass
 * E. u. var. versicolor - bears pinkish-brown flowers with bright stripes

Distribution and habitat
It is native to western North America from California to Colorado to central Canada, where it is abundant and found in many habitats, including the sagebrush steppe and alpine areas.

Ecology
It is a popular larval host, feeding the bramble hairstreak, desert green hairstreak, lupine blue, Mormon metalmark, Rocky Mountain dotted blue, Sheridan's hairstreak, Sonoran metalmark, and western green hairstreak. Additionally, goats and domestic sheep feed on the plant.

Cultivation
The wildflower gardening author Claude A. Barr complemented sulphurflower buckwheat as a "treasure in appearance and in adaptation in my garden." It is valued for its very low water usage for xeriscaping. The cultivar "Kannah Creek", a selection of Eriogonum umbellatum var. aureum, has been introduced to the garden trade by the Plant Select cooperative sponsored by Colorado State University and Denver Botanic Gardens. It grows in USDA zones 4–8.