Animal DNA degrades over time (biological aging), due to shortening of telomeres, mutations, etc. But why can you take a cutting of a plant of a certain age and the cutting seemingly resets its biological clock? A cutting from a 30 year old plant will live a full lifespan, versus lifespan – 30 years.
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Plants that are cloned are generally cloned by cutting from new growth (soft or semi-softwood cuttings from plant bits that grew this year). New growth has, by definition, not had much chance to age. The new growth puts out roots, then as it ages puts out more new growth. The original growth doesn’t clone, it’s the new growth that does. So the total age of the bit of plant that you’re actually growing is never all that excessive.
That said, cloned plants do mutate. If you take cuttings from a part of the plant that likes to grow vertically, for example, the plant that is produced will grow more vertically (this is called a “sport”). Similarly, if you buy a popular plant that is an unusual color, parts of the plant will often revert to the plant’s “natural” color as the plant ages. Maybe it’s better to think of plants as “colonies” of organisms. Because they don’t have complex organs, any given bit of a plant can have its own genetics and still survive as long as there are roots below piping it water/nutrients and leaves above piping it energy.
Many plants reproduce asexually; sometimes exclusively, sometimes not.
Consider the humble potato. It grows from a tuber, then grows more tubers. In its original native environment of mountainous Peru, a landslide might just knock some potatoes down to a lower level where they can just keep growing. Mints and many grasses spread through runners (stolons) more than through seeds.
*Oxalis* (woodsorrel, sourgrass) is a funny case: some species such as *O. pes-caprae* reproduce exclusively asexually, through bulbs and runners; others, such as *O. oregana* reproduce asexually with runners and sexually with seeds.
All asexual reproduction is effectively a specialized form of cloning.
Many plants (most perennials) are functionally immortal, specifically because of this reproduction by cutting, which essentially creates a clone of the parent plant. This is similar to bacteria and other very simple organisms which simply divide themselves to reproduce.
A current theory is that clonal reproduction is the most basic way to for a species to keep itself alive. In contrast, plants and animals that reproduce sexually are more likely to age and die off, the idea being that sexual reproduction can create a more diverse descendent that may be better suited to survive Thus, the parent organism(s) should die off after reproducing to reduce competition with their own descendants.
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