Mammillaria herrerae aka Golf's Ball Cactus

Mammillaria herrerae is a small Mexican cactus in the Cactaceae family. Its round, white body gives it the name golf ball cactus. Kew places its native range from Guanajuato to Hidalgo. LLIFLE describes a much smaller range in Querétaro. There, it grows among grasses and on sloping limestone rocks. Its habitat is open, dry scrub. Illegal collecting has caused steep losses in wild plants. LLIFLE reports its conservation status as Critically Endangered.

Most plants have one stem, though some form basal clusters. The stem starts round and may lengthen with age. Its usual height and width are 0.07–0.11 feet [0.02–0.035 metres]. Cultivated plants can slowly reach 0.26 feet [0.08 metres] tall. The stem has no milky sap. Closely packed tubercles have a cylindrical shape and blunt ends. Dense white or grey spines lie close against the body. The radial spines interlace, with 100 or more in each group. There are no central spines. This coat shades the stem and traps air near it. It helps buffer the plant against heat and cold.

Flowers open during the day in April and May. Their colour ranges from pale pink to reddish violet. Each flower measures about 0.07–0.08 feet [0.02–0.025 metres] long. They look large against the small stem. Plants start to bloom at about five to seven years old. They must also reach roughly 0.10 feet [0.03 metres] across. The small, round fruits are whitish. Their seeds are dark brown to nearly black.

In cultivation, this cactus needs a mineral mix that drains freely. LLIFLE advises a moderately acidic mix without peat or other humus. It also advises against adding limestone to the pot. Water lightly while the plant grows, then stop for winter. Avoid humid air during its winter rest. Too much water and shade can cause swollen, misshapen growth. The supplied species evidence gives no firm frost limit.

Rot is a key concern when growing this small cactus. Use a small pot with drainage holes and very porous compost. LLIFLE suggests repotting at two- to three-year intervals. During growth, it recommends feed low in nitrogen. The feed should supply more potassium and phosphorus. Its white spines and spring flowers provide its main visual interest. The supplied evidence does not establish food uses or toxicity.