STOLON

A stolon is a specialized type of horizontal above-ground shoot, a colonizing organ that arises from an axillary bud near the base of the plant. The stolon differs from the typical vegetative shoot of that same plant in having much longer and, typically, thinner internodes, and the horizontal stolon also has a strong tendency to form adventitious roots at the nodes.

A mother plant produces stolons often in several compass directions, permitting cloning, i.e., vegetative reproduction, by producing young ramets (plantlets) around the plant. The stolon, connecting mother plant with each ramet, initially provides the pathway for a flow of nutrients and water to the new plantlet, or even some nutrients from the plantlet back to the mother plant, but that physical connection is eventually severed or becomes dysfunctional as the plantlet develops its nutritional independence. After the stolons are severed, a mother plant is encircled by satellite plantlets, which soon grow larger, filling in any space between the plants. In this way, stoloniferous species usually colonize open ground by forming a continuous ground cover, and thereby can exclude other species by crowding them out. Understandably, therefore, many species that have been domesticated as turfgrasses and ground covers are stoloniferous, forming dense clonal monocultures.

The most common textbook example of a stolon is the strawberry (Fragaria), in which the mother plant forms plantlets on stolons during spring growth. In the case of strawberry, the stolon is often termed a runner. Some authors treat a runner as a specialized form of the stolon, in which the leaves on the stolon are reduced to very small or minute scales, in contrast to the stolon, on which some leaf blade can be observed, so that the stolon is actually a photosynthetic unit. By itself, a runner is not a self-sustaining structure, merely a connector between ramet and mother plant. In both cases, the leaves of the typical vegetative shoot are different from the stoloniferous shoots, i.e., the plant is heteroblastic.

Many plants that have above-ground stolons also form horizontal, below-ground rhizomes. Good examples of this can be found among grasses, such as bermudagrass (Cynodon dactylon).

Numerous plants grow by forming stems next to the substrate. If the plant is lying on the substrate but does not form adventitious roots, the growth habit is termed procumbent. If the plant is lying on the substrate and forms adventitious roots, the growth habit is termed either repent or stoloniferous. Using the term stoloniferous generally requires that the plant must have two different types of vegetative shoots, not only one type, the creeping shoot.

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