Mammillaria knippeliana Quehl

Solitary, eventually clustering, body globular, to 5 cm wide. Tubercles prominent. Axils woolly and bristly. Central spines lacking. Radial spines 4-6, to 30 mm, white, tips reddish-brown. Flowers yellowish, 1.5 cm long, 1 cm wide. Fruit red.

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.