Rediscovered in 2005 by B. Schafer, M. Widdowson, and R. Preston; last seen in 1892. Known only from the Montezuma Hills; all other reports have been misidentifications. Easily confused with P. acanthocarpus, P. trachycarpus, and others. Habitat between the Motezuma Hills and Elmira should be surveyed for additional occurrences. Threatened by disking, development, and non-native plants. See Contributions of the U.S. National Herbarium 22:79-113 (1920) for original description, Contributions from the Arnold Arboretum 3:5-82 (1932) for revised nomenclature, and Madroño 57(4):242-245 (2010) for discussion of rediscovery.