Campanula exigua Rattan (1886) Ravenella exigua, the chaparral bellflower, rock harebell, or Rattan campanula, is an annual flowering plant in the bellflower family Campanulaceae.

The plant is endemic to Mount Diablo, in the northern Diablo Range within Contra Costa County, in the East Bay region of northern California.

It grows amongst other Mount Diablo and regional endemic plants, all dependent on natural fire ecology conditions.

Ravenella exigua sends up several long stems filled with milky sap and bearing sparse, tiny leaves.

At the end of each stem grows a bell-shaped bright blue-violet flower.