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With a few exceptions, all plants have chloroplasts. Chloroplasts are the organelles responsible for photosynthesis in plants. Interestingly, chloroplasts have their own genome -- called a plastome -- which is separate from the nuclear genome. The genetic composition of ferns, gymnosperm, and angiosperm plastomes are remarkably similar, revealing very little change over evolutionary time. There are however a few notable exceptions to the apparent stability of the plastome. A few lineages of both angiosperm and gymnosperm show dramatically higher rates of mutation and genetic rearrangement than those of their relatives, suggesting major genome destabilization. Vittariods are a group of ferns that live on the trunks and in the branches of trees in forests. Vittariods are so unique among ferns in structure and life cycle that they have long been thought to be their own family, but recent genetic research has shown they reside within the genus Adiantum. Vittariods bear little resemblance to their closest relatives and appear to have quite rapidly diverged from them.

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