Isomeris arborea Nuttall var. angustata Parish, Muhlenbergia 3: 128. 1907; I. arborea var. insularis Jepson

Capsules not inflated, narrowly fusiform (long-attenuate at both ends).

Flowering summer. Hillsides, grasslands, desert washes and flats, roadsides; 0-1300 m; Ariz., Calif.; Mexico (Baja California, Colima, Sonora).

Variety angustata is found in the Colorado and Mojave deserts and in western and northwestern Mexico, including offshore islands (e.g., Revillagigedo Islands). Plants with particularly narrow capsules from Cedros Islands (Baja California) have been distinguished as var. insularis.