They are one of the largest genuses and are very popular in cultivation. Mainly the range is between south-western US to Mexico, however others are found in the West Indies to northern South America. The size of some grows to less than 1" whereas others cluster growing to 1' wide. The flowers are small and in rings near the crown and often last for a few weeks. The length of the spines can be varied and also hooked or covered with hair. The name is derived from a Latin word, mammilla, which more or less means nipple and it relates to the way tubercle shape of the cacti.
Mammillaria bocasana has a common name as Powder Puff due to its white, hair spines. It is found in Mexico and can tolerate temperatures down to -7° centigrade (c. 19° fahrenheit).
I have taken a few cuttings of Mammillaria gracilis and with a bit of luck, I will have a few, which will show their yellow flowers.
As you will see by size of the pictured Mammillaria gracilis Arizona Snowcap, it is relatively young. It is a variant of M. gracilis.
I cannot say any more than this cactus is Mammillaria demispina and as shown in the picture, its got white spines.
Mammillaria elongata is commonly known as either Golden Stars or Lady Fingers. Their natural habitat is central Mexico. When it comes to temperature, the minimum they should have is 10° centigrade (c. 50° fahrenheit), which obviously means if kept in a greenhouse, a heater will be required. As seen, they clump and if they are used as cuttings, they easily grow.
This Mammillaria lahata is another cactus that has got me. All I can say is its got small white spines and clusters.
Mammillaria marksiana in wild can grow to 4" however in cultivation it can double in size. It should not be watered from above as it would ruin the fine wool.
I do not have a great deal of information on Mammillaria microhelia, but I am aware that its natural habitat is in Mexico and its temperature can drop to -4° centigrade (c. 25° fahrenheit).
A picture is to follow however Mammillaria plumosa is covered with white hair and it clusters. The flowers are yellow with them showing in the spring. They are found in Mexico and due to the location the cacti can survive if the temperature drops to minus 10° centigrade (14° fahrenheit).
Adromischus ~ Astrophytum ~ Cephalocereus ~ Cereus ~ Cyanotis ~ Echinopsis ~ Epiphyllum ~ Espostoa ~ Ferocactus ~ Frithia ~ Gymnocalycium ~ Haworthia ~ Hildewintera ~ Lithops ~ Lophocereus ~ Notocactus ~ Opuntia ~ Pilosocereus ~ Rebutia ~ Schlumbergera ~ Sedum ~ Sempervivum ~ Stenocereus ~ Sulcorebutia ~ Tephrocactus ~ Turbinicarpus ~ Weberbauerocereus