Grusonia clavata

Genus Grusonia was created  for small North American Opuntoides that distinguish from Cylindropuntias by lack of papery spin cover - 'sheath'. They are low spreading plants, often forming mats, and easily noted for downward pointing spines. Grusonia clavata is more often than other species seen in collections, for it's compact growth and dagger-like spines.
Grusonia buds are also easily recognized for they shape with distinct long 'tube'. The plant in picture had only two mature segments a that time, and was ready to flower at the size.