Chimeras in botany are single organisms composed of two genetically different types of tissue. They occur in plants, on the same general basis as with animal chimeras. However, unlike animal chimeras, both types of tissues may have originated from the same zygote, and the difference is often due to mutation during ordinary cell division.
The best known are those chimeras cultivated for plant variegation. Generally the genetic difference is due to mutation in meristematic tissue of a normal plant. For most variegation, the mutation involved is the loss of the chloroplasts in the mutated tissue, so that part of the plant tissue has no green pigment and no photosynthetic ability. Other types of chimeras are preserved because the skin tissue lacks the thorn producing characteristic of the underlying tissue.
Another type of plant chimera is the graft-hybrid, where tissues have partially fused together following grafting. The best known example of this is + Laburnocytisus adamii, caused by a fusion of a laburnum and a broom.
Because chimeras have more than one type of genetic material, while they may produce viable offspring from seed, these will not be true to type. All propagation that preserves the variation has to be by cuttings or division. Some types of cuttings, such as root cuttings, will produce entirely new growing points, usually from the inner one of the two types of tissue, so that these cannot be used either.
