A variety is a recognised division of a species, especially in botany; in zoology, species are divided into subspecies rather than varieties.
The pincushion cactus, Escobaria vivipara (Nutt.) Buxb., is a wide-ranging variable species occurring from Canada to Mexico, and found throughout New Mexico below about 8500 feet. Nine varieties have been described. Where the varieties of the pincushion cactus meet, they cross-breed. The Escobaria vivipara var. arizonica is from Arizona while the Escobaria vivipara var. neo-mexicana is from New Mexico.
A domesticated variety of a plant is called a cultivar, while a domesticated variety of an animal is called a breed.
A cultivar is indicated with a cv. and by putting the name between quotes, e.g. Aeonium arboreum cv. "Atropurpureum".
A strain, especially in bacteriology, is a collection of descendants of a single significant ancestor, and is sometimes used interchangeably with 'variety' but this is not strictly correct. A strain of animals is usually called a bloodline.
