The genus Tephrocactus includes the Cholla. They are jointed plants, rather than columnar or rather spherical.
This one is a bit intermediate.
I have several species in this genus, some decades old, and this (recently acquired) is the first to flower for me.The bud took weeks to develop.
Olympus EM-1 (aperture priority), Olympus 4/3 50mm f2 macro, f 13 or f11 ISO 250, hand-held.
Stereos will be uploaded tomorrow.