Chaos Jumbles in Lassen Volcanic National Park CA, where these plants were photographed in August, is perfect habitat for shaggy hawkweed (Pilosella horridum). This member of the Sunflower Family (Asteraceae) prefers rocky slopes, granite crevices and other dry, open rocky areas from 5,000 to 10,800 feet. A perennial, shaggy hawkweed is native to California and parts of Oregon and Nevada.
All the herbage on shaggy hawkweed is covered in long, soft, white or brown hairs. Several branching stems arise from a taproot. The spatula-shaped leaves have entire margins and hair on both sides of the blade. Most leaves are at the base and lower half of the stem. When the stems or leaves are broken they exude a milky substance.
The shaggy hawkweed inflorescence contains many small flower heads. The yellow flower heads are composed entirely of ray flowers, the ligules of which are notched at the tips. Shaggy hawkweed seeds are brown achenes with white pappi.
Until recently P horridum was a member of the genus Hieracium. Pilosella, the current genus designation, comes from Latin: pilus/pilosus meaning hair/hairy. Also derived from Latin, the species name means “bristly”. Prickly hawkweed is another common name for P horridum.
The ancient Greeks believed that hawks would tear apart a plant called the hieracion (from hierax/hawk) and wet their eyes with the juice to clear their eyesight. The former genus name (Hieracium) and the common name come from this belief.