K. Heil

High proportion of cactus species threatened with extinction

George D. Gann, A. P. Ferreira, A. Búrquez, 2015, Nature Plants.

Vascular Flora and Vegetation of Capitol Reef National Park, Utah

J. Porter, W. H. Romme, K. Heil, 1993 .

A Preliminary Catalog of the Vascular Plants of the Chama Land and Cattle Company—Frank Sims Ranch, Rio Arriba County, New Mexico

K. Heil, 2007 .