Eriocactus (Parodia) leninghausii

Eriocactus leninghausii is a common in cultivation plant, South America native. It is easy to grow, and reaches flowering size of about 4-5 inches tall in several years from seed. Plants are often sold in garden centers.
Flower size depends on the size of the plant, and on mature plants they are at least twice larger. Nice silky texture of the flower 'petals' (strictly speaking not the proper term for cacti) makes the blooms very special.
Several plants I have blooming repeatedly over all summer, and sometimes also off  season. Common cactus culture suits them well,