Mammillaria pettersonii Hildm.

Solitary, body globular, to 30 cm wide. Tubercles prominent, 3-angled. Axils woolly. Central spines 4, 10-15 mm long, whitish or yellowish-brown, tips black, lowermost to 20 mm. Radial spines 10-12, 2-9 mm long, whitish or yellowish-brown, tips black. Flowers deep pink with darker central stripe, 2.5 cm long and wide. Fruit purplish-pink.

C Mexico

Source: Thompson, A, ; Forbes, S.; Spencer, R. (1997). Cactaceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.

kingdom Plantae
phylum   Tracheophyta
class    Magnoliopsida
superorder     Caryophyllanae
order      Caryophyllales
family       Cactaceae
genus        Mammillaria Haw.