Wikipedia
Acanthocalycium
Acanthocalycium is a genus of cactus consisting of several species from Argentina. The taxon name comes from Greek akantha (meaning prickly) and kalyx (meaning buds), which refers to the spines on the floral tubes.
These plants are globose to elongate, with numerous ribs on the spiny stems. Flowers range from white to pink to red and open during the day.