Astrophytum asterias (a.k.a. Sea-Urchin Cactus or Sand Dollar) is an extremely flat barrel cactus with unique and remarkably beautiful form and no typical covering of spines, but with tiny speckled tuft of hairs less than pinhead-sized.
It produces large yellow flowers with orange throats often larger than the plant itself. The common name comes from resemblance to sea urchin without spines.