Population Surveys and Viability Assessments for Coryphantha scheeri var. Robustispina, a Federally Protected Cactus of the Sonoran Desert

Coryphantha scheeri var. robustispina (Pima pineapple cactus [PPC]; Cactaceae) is a small cylindrical cactus found in semi-desert grassland and Sonoran desert-scrub in southern Arizona and northern Mexico. This species was listed as endangered in 1993 in the USA, but does not have protection in Mexico. In 2017, surveys were repeated at six PPC sites with a long monitoring history within the Altar Valley, Pima County, Arizona. Overall, PPC individuals were found at five of the six sites (i.e., 83%). Although PPC is persisting at most sites and recruitment was observed at some sites, the overall pattern was one of decline within the surveyed area. In addition, population viability analyses predict that four sites will lose more than half of their individuals within 20 y, and five sites within 50 y. The information presented in this study should be useful for making decisions regarding federal protection for Coryphantha scheeri var. robustispina.