Mammillaria sp.

Life and Mathematics. Logarithmic spiral. 13 left hand spirals and 8 right hand spirals: two consecutive terms of the Fibonacci series: 1,1,2,3,5,8,13,21,34, 55, 89, ...
Mammillarias have extremely variable spination from species to species, and attractive flowers, making them specifically attractive for cactus hobbyists. Most mammillarias plants are considered easy to cultivate, though some species are among the hardest cacti to grow. Several taxa are threatened with extinction at least in the wild, due to habitat destruction and especially overcollecting for the pot plant trade. Cactus fanciers can assist conservation of these rare plants by choosing nursery-bred specimens (wild-collected ones are illegal to possess for the rarest species anyway). Besides helping to preserve rare plants, one can gain experience in growing and breeding cacti in general with nursery-bred rare mammillarias: several mammillarias are quite easy (for cacti) to grow from seeds.