Closeup of an Old Lady Cactus and its flower / 仙人掌花近攝

It's not easy to see a cactus with flowers, but when I went to the University of Michigan Matthaei Botanical Gardens (in Ann Arbor, Michigan), I saw many strange cactuses blooming in the Conservertory. The cactus in this photo is the Old Lady Cactus (Mammillaria Hahniana, Cactaceae).