  
 
Mammillaria is arguably the most popular cactus genus in cultivation. Mammillarias have extremely variable spination from species to species, and eye-catching flowers, making them specifically attractive for cactus hobbyists. Most Mammillaria plants are considered easy to cultivate. The genus Mammillaria is one of the largest in the Cactaceae family, with currently over 200 known species and varieties recognized. Mammillarias are native to Mexico, southwest USA, the Caribbean, Colombia, Venezuela, Guatemala and Honduras. The first was described by Carolus Linnaeus as Cactus mammillaris in 1753, deriving its name from Latin mammilla, "nipple", referring to the tubercles that are one of the plant's specific features.   
  In 1812, the cactus specialist Adrian Haworth described the genus Mammillaria to contain this and related species. Numerous species are commonly known as nipple cactus, fishhook cactus or pincushion though such terms may also be used for related taxa such as Escobaria. Mammillaria species can be grown as pot plants and make interesting features on a sunny veranda or windowsill. They also make an attractive addition to a rockery or water-wise garden.
 The variation in spines is a novel selling feature and often, these plants fit the stereotypical expectations that most people have for a cactus plant, although some species are only going to be found among highly-dedicated cactus growers. The popularity of this genus has led to a good deal of study and consequent literature on both growing and identifying Mammillaria species.
Mammillaria geminispina or Twin-spine Cactus is native to Hidalgo, Queretaro and San Luis Potosi in central Mexico occurring at altitudes of 1000 to 1859 m. They are clump forming cacti with individual stems reaching 18 cm tall and 5cm in diameter. The plants are covered in white hairy spines making clumps appear white. There are 16 to 20 needle-like radial spines about 5 to 7 mm long and 2 long erect central spines up to 40mm in length. The flowers appear in summer and autumn, and are deep pink to carmine red, followed by carmine red fruits.
  
  
  
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