Fragmentation or clonal fragmentation in multicellular or colonial organisms is a form of asexual reproduction or cloning in which an organism is split into fragments. Each of these fragments develop into mature, fully grown individuals that are clones of the original organism.
The splitting may or may not be "intentional"- it may occur due to man-made or natural damage by the environment or predators. This kind of organism may develop specific organs or zones that may be shed or easily broken off. If the splitting occurs without the prior preparation of the organism, both fragments must be able to regenerate the complete organism for it to function as reproduction.
Fragmentation as a method of reproduction is seen in many organisms such as filamentous cyanobacteria, molds, lichens, many plants, and animals like sponges, acoel flatworms, some annelid worms, and sea stars.
Moulds, yeasts, and mushrooms, all of which are part of the Fungi kingdom, produce tiny filaments called hyphae. These hyphae obtain food and nutrients from the body of other organisms to grow and fertilize. Then a piece of hyphae breaks off and grows into a new individual and the cycle continues.
Many lichens produce specialised structures that can easily break away and disperse. These structures contain both the hyphae of the mycobiont and the algae(phycobiont) (see soredia and isidia. Larger fragments of the thallus may break away when the lichen dries or due to mechanical disturbances(see the section on reproduction in lichens).
Fragmentation is a very common type of vegetative reproduction in plants. Many trees, shrubs, nonwoody perennials, and ferns form clonal colonies by producing new rooted shoots by rhizomes or stolons, which increases the diameter of the colony. If a rooted shoot becomes detached from the colony, then fragmentation has occurred. There are several other mechanisms of natural fragmentation in plants.
When the splitting occurs due to specific developmental changes, the terms architomy, paratomy and budding are used. In architomy the animal splits at a particular point and the two fragments regenerate the missing organs and tissues. The splitting is not preceded by the development of the tissues to be lost. Prior to splitting, the animal may develop furrows at the zone of splitting. The headless fragment has to regenerate a complete head.
In paratomy, the split occurs perpendicular to the antero-posterior axis and the split is preceded by the "pregeneration" of the anterior structures in the posterior portion. The two organisms have their body axis aligned i.e. they develop in a head to tail fashion. Budding can be considered to be similar to paratomy except that the body axes need not be aligned: the new head may grow toward the side or even point backward (e.g. Convolutriloba retrogemma an acoel flat worm).
Many types of coral colonies can increase in number by fragmentation that occurs naturally or artificially. Within the reef aquarium hobby, enthusiasts regularly fragment corals for a multitude of purposes including shape control; selling to, trading with, or sharing with others; regrowth experiments; and minimizing damage to natural coral reefs. Both hard and soft corals can be fragmented, with the level of success depending on the skill of the aquarist, method used, tolerance of the specific species, and conditions of care. Genera that have shown to be highly tolerant of fragmentation include Acropora, Montipora, Pocillopora, Euphyllia, and Caulastraea among many others.
In echinoderms, the process is usually known as fissiparity (a term also used infrequently for fission in general). Some species can intentionally reproduce in this manner through autotomy. This method is more common during the larval stages.
As this process is a form of asexual reproduction, it does not produce genetic diversity in the offspring. Therefore, these are more vulnerable to changing environments.