Nichol's Turk's head cactus (Echinocactus horizonthalonius var. nicholii) is one of multiple species of Echinocactus horizonthalonius. The Nichol's Turk's head cactus ranges from blue-green to yellow-green. It tends to be around 46 centimeters tall and has about a 20 centimeter diameter. It has 8 ribs that are lined with spines. The cactus blooms from April to May with a purple flower and white, hairy fruit. Like many cacti, it is rather slow growing at a rate of just 2 inches in 10 years, due to minimal nutrient input. Its habitat is located mainly in the Vekol and Waterman Mountains in Arizona and it has a population in the Sierra del Viejo Mountains of northwestern Sonora. The cactus is particularly fond of Horquilla limestone outcrops. The biggest threats to these cacti are habitat loss to new development, vehicle/off-roading damage, mining, and human collection. Among other threats, erosion from foot traffic from drug and human trafficking in the area.