Nichol's Turk's Head Cactus (Echinocactus horizonthalonius Lemaire var. nicholii L. Benson) was listed as endangered in the United States in 1979. This species occurs in a few known populations in southern Arizona and northern Mexico. Since the 1990s we have monitored a population in southern Arizona, examining growth rates, recruitment, flowering, mortality, and other aspects of this cactus related to demography and ecology. Our over-arching aim is to better understand their biology and to contribute information relevant to their protection.

Working group: Drs. Margrit McIntosh, Amy Boyd, Lucinda McDade, Robert Steidl, and Betsy Arnold, based at the University of Arizona.

For some of our recent work, please see McIntosh et al. 2019 (growth, demography), Boyd et al. 2022, and Arnold et al. 2022. Data are available online at figshare - please contact Betsy Arnold for the link.. Team members and some of our many volunteers are included in the images below. For additional information, please contact Betsy Arnold.