Its common names include purple owl's clover, escobita, and exserted Indian paintbrush.

Castilleja exserta is an annual herb about 100–450 millimetres (4–18 in) tall with a hairy stem covered in thready leaves.

Although this species is variable in appearance and easily hybridizes with other Castilleja species, it generally bears a brightly colored inflorescence of shaggy pink-purple or lavender flowers.

The thin, erect bracts are usually tipped with the same color, giving the inflorescence the appearance of a paintbrush.

[4] Varieties include: This is a crucial host plant for the Bay checkerspot butterfly (Euphydryas editha bayensis), which is a threatened species that is endemic to the San Francisco Bay region in California.