Myrtillocalycium 'Polyp'.  a graft chimera between Myrtillocactus geometrizans and Gymnocalycium cv. Red Hibotan

Cactus Guide.com provides an interesting definition of chimera - 

Chimera (pl. chimaera) A plant that contains a mixture of tissues from two or more genetically different cells or tissues in the same part of a plant. These can be spontaneously mutated cells of the host organism or cells from a different organism or species produced as a result of organ transplant, grafting (Graft chimera), and artificial fusion of unlike tissues or genetic engineering. The name chimera derives from the Old French, from Latin "chimaera", from Greek "khimaira", which means chimera, she-goat. From Indo-European Root "ghei-" Chimera is a Greek mythological character a fire-breathing she-monster made up of the front parts of a lion, the middle parts of a goat, and the tail of a snake she is the daughter of Typhon.