Echinocactus horizonthalonius var. nicholii
The Nichol Turk's head cactus ranges from blue-green to yellow-green. It is a barrel cactus, reaching a maximum height of 18 inches and diameter of eight inches. It has eight ribs which spiral on the trunk. Spines are found on the ridges of the plant, with three central spines and five radial spines. The flowers are pink-magenta and bloom from April to May. The fruits are covered with white, wooly hairs. This cactus is very slow-growing, taking ten years to reach a height of two inches. It is a federally endangered species.
Occurs in semi-arid Sonoran desert scrub. It persists on limestone outcroppings and limestone derived soils in incline terraces, saddles, and alluvial fans at elevations from 2,400 to 4,100 feet (732-1250 m).
This cactus was seen at the Arizona-Sonora Desert Museum as part of their botanical collection. We were there in October and were lucky to see the late bloom on this cactus.