Ancistrocarphus keilii is a rare species of flowering plant known by the common name Santa Ynez groundstar.

[3] Ancistrocarphus keilii grows in sandy soils in chaparral habitat adjacent to oak woodlands.

The plant is considered to be vulnerable to extinction because of its rarity, its populations are located in habitat that is likely to be disturbed or developed, and because it apparently has no effective method of biological dispersal.

The leaf blades are borne on petioles with thin, expanded bases that surround the inflorescence.

The tiny achene generally germinates directly next to its parent, so that the plants become a carpetlike layer.