Hieracium piloselloides is an erect perennial, with a milky sap that can grow from 8-40 in. (20.3-101.6 cm) tall.
Foliage
Leaves are mostly basal, pale green to whitish with soft hairs. The smooth stems are mostly leafless or with 1-2 small leaves.
Flowers
Flower heads are clustered, yellow, 0.5 in. (1.3 cm) wide, and number up to 30 per plant. This plant blooms June-September.
Fruits
The fruit is a dark brown that is flattened with clusters. It is very hairy.
Ecological Threat
Hieracium piloselloides produces mats of rosettes that dominate sites by out-competing other species for water and nutrients and by releasing alleopathic compounds from their own decaying leaves. They grow well in moist sunny grassy areas, but can tolerate some shade. They are becoming troublesome weeds in native meadows, prairies, pastures and lawns. Wilderness areas in the Pacific Northwest are at risk of invasion.