Eucephalus glabratus is a North American species of flowering plant in the aster family known by the common name Siskiyou aster. It grows in brushland or in openings in conifer forests in the mountains of southwestern Oregon and northwestern California. Eucephalus glabratus is a perennial herb up to 60 cm (24 inches) tall, with branching rhizomes. Stems and leaves are hairless or nearly so. One plant will usually produce 3-8 flower heads per stem. Each head has 0-4 violet ray florets surrounding numerous yellow disc florets.