These beautiful golden yellow flowers belong to the Golden Barrel Cactus (Echinocactus grusonii), otherwise known as Mother-In-Law’s Cushion.
Image taken in north central Victoria, Australia.

Camera Olympus E-30, Focal length 42.0,
Shutter speed 1/800s, f/9.0, ISO 200.

Echinocactus grusonii is a well known species of cactus native to central Mexico from San Luis Potosi to Hidalgo. Described by Heinrich Hildmann in 1891, it is popularly known as the Golden Barrel Cactus, Golden Ball or, amusingly, Mother-in-Law’s Cushion. It belongs to the small genus Echinocactus, which together with the related genus Ferocactus, are commonly referred to as barrel cacti.
Despite being one of the most popular cacti in cultivation, it is rare and critically endangered in the wild.
Growing as a large roughly spherical globe, it may eventually reach over a meter in height after many years. There may be up to 35 pronounced ribs in mature plants, though they are not evident in young plants, which may have a knobbly appearance. Note: Younger Golden Barrels do not look similar to the mature ones. The sharp spines are long, straight or slightly curved, and various shades of yellow or, occasionally, white. Small yellow flowers appear in summer around the crown of the plant, but only after twenty years or so.