Vegetative reproduction

Vegetative reproduction (vegetative propagation, vegetative multiplication, vegetative cloning) is a form of asexual reproduction in plants. It is a process by which new organisms arise without production of seeds or spores. It can occur naturally or be induced by horticulturists.

Although most plants normally reproduce sexually, many have the ability for vegetative propagation, or can be vegetatively propagated if small pieces are subjected to chemical (hormonal) treatments. This is because meristematic cells capable of cellular differentiation are present in many plant tissues. Horticulturalists are interested in understanding how meristematic cells can be induced to reproduce an entire plant.

Success rates and difficulty of propagation vary greatly. For example, willow and coleus can be propagated merely by inserting a stem in water or moist soil. On the other hand, monocotyledons, unlike dicotyledons, typically lack a vascular cambium and therefore are harder to propagate.

In a wide sense, methods of vegetative propagation include cutting, vegetative apomixis, layering, division, budding, grafting and tissue culture. Cutting is the most common artificial vegetative propagation method, where pieces of the "parent" plant are removed and placed in a suitable environment so that they can grow into a whole new plant, the "clone", which is genetically identical to the parent. Cutting exploits the ability of plants to grow adventitious roots (i.e. root material that can generate from a location other than the existing or primary root system, as in from a leaf or cut stem) under certain conditions. Vegetative propagation is usually considered a cloning method. However, there are several cases where vegetatively propagated plants are not genetically identical. Root cuttings of thornless blackberries will revert to thorny type because the adventitious shoot develops from a cell that is genetically thorny. Thornless blackberry is a chimera, with the epidermal layers genetically thornless but the tissue beneath it genetically thorny. Similarly, leaf cutting propagation of certain chimeral variegated plants, such as snake plant (Sansevieria trifasciata), will produce mainly nonvariegated plants. Grafting is often not a complete cloning method because seedlings are used as rootstocks. In that case only the top of the plant is clonal. In some crops, particularly apples, the rootstocks are vegetatively propagated so the entire graft can be clonal if the scion and rootstock are both clones. Apomixis (including apospory and diplospory) is a type of reproduction that does not involve fertilisation. In flowering plants, unfertilized seeds are involved, or plantlets that grow instead of flowers. Hawkweed (Hieracium), dandelion (Taraxacum), some citrus (Citrus) and many grasses such as Kentucky blue grass (Poa pratensis) all use this form of asexual reproduction. Bulbils are sometimes formed instead of the flowers of garlic.

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