Stolon

  Stolons are horizontal stems which grow at the soil surface or below ground. They form new plants at the ends or at the nodes. Stolons are often called runners. Imprecisely they are stems that run atop or just under the ground; more specifically, a stolon is a horizontal shoot from a plant that grows on top of or below the soil surface with the ability to produce new clones of the same plant from buds at the tip.^[1]

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Stolons are stems

Stolons are similar to normal stems except they produce adventitious roots at the nodes and run horizontally rather than vertically. They also have long internodes with reduced leaves, with the exception of stolons in aqueous plants. Plants with stolons are called stoloniferous. A stolon is a plant propagation strategy akin to a rhizome. The complex formed by a mother plant and all its clones connected by and/or produced from stolons form a single genetic individual. Runners are aboveground stolons and are produced by many plants, for example strawberry. Stolons are different from rhizomes because they do not have the same reduced leaves that rhizomes have at the nodes but have scale-like leafs. Typically, stolons have very long internodes and form new plants at the ends which form shoots which rise to the soil surface and produce foliage and/or flowers. In contrast, rhizomes most often have short internodes with leaf-scars and thin paper-like leaves and root along the under side of the stem. Root formation does not correspond strictly to the nodes but roots can generate from areas around the scar-like nodes as well.

Morphology

  Stolons are like long branches of a tree that grow horizontal to the soil surface and produce new plants at the ends, they have nodes and internodes, leaves that are reduced to scales and buds that grow into roots and shoots. Stolons arise from the base of the plant,^[2] in strawberries the base is above the soil surface, in many bulb forming species and plants with rhizomes, the stolons arise under ground and remain underground and form shoots that rise to the surface at the ends or from the nodes. The nodes of the stolons produce roots, often all around the node and hormones produced by the roots seem to cause the stolon to initiate shoots with normal leaves.^[3] Typically after the formation of the new plant the stolon dies away^[4] in a year or two, while rhizomes persist normally for many years or for the life of the plant, adding more length each year to the ends with active growth. Rhizomes are used as storage structures for nutrients and most often are covered with thin papery leaves (normally a translucent brownish color), while stolons are not covered with reduced leaves but have scales like leaves at the nodes that are most often white in color. Stolons look and act like etiolated stems except for their orientation of growth, instead of stretching upward for light they grow laterally or downward. The horizontal growth of stolons results from the interplay of different hormones produced at the growing point and hormones from the main plant, with some studies showing that stolon and rhizome growth effected by the amount of shady light the plant receives with increased production and branching from plants exposed to mixed shade and sun, while plants in all day sun or all shade producing fewer stolons.^[5]

Often the general meaning of stolon (horizontal stems above ground) does not distinguish morphologically the differences between stolons and rhizomes but just differentiates rhizome and stolon from each other strictly by where they are found, with rhizomes being below ground. Though this generalization is imprecise with a number of plants having soil level or above ground rhizomes including Iris species and many orchid species. Because of this some botany texts now use the term underground stolon to refer to stolons that move under ground.^[6]

T. Holm (1929) restricted the term rhizome to a horizontal, usually subterranean, stem that produces roots from its lower surface and green leaves from its apex, developed directly from the plumule of the embryo. He recognized stolons as axillary, subterranean branches that do not bear green leaves but only membranaceous, scalelike ones.^[7]

Plants with stolons

  In some Cyperus species the stolons end with the growth of tubers; the tubers are swollen stolons that form new plants^[8].

Some species of crawling plants can also sprout adventitious roots, but are not considered stoloniferous: a stolon is sprouted from an existing stem and can produce a full individual. Examples of plants that extend through stolons include some species from the genera Argentina (silverweed), Cynodon, Fragaria, and Pilosella (Hawkweeds), Zoysia japonica, Ranunculus repens.

Other plants with stolons below the soil surface include many grasses, Ajuga, Mentha,^[9] and Stachys.

Lily-of-the-valley (Convallaria majalis) which has rhizomes that grow stolon-like stems called stoloniferous rhizomes or leptomorph rhizomes. A number of plants have stoloniferous rhizomes including Asters^[10] These stolon-like rhizomes are long and thin, with long internodes and indeterminate growth with lateral buds at the node that mostly remain dormant.

In potatoes, the stolons^[11] start to grow within 10 days of plants emerging above ground, with tubers usually beginning to form on the end of the stolons.^[12] The tubers are modified stolons^[13] that hold food reserves with a few buds that grow into stems. Since it is not a rhizome it does not generate roots, but the new stem growth that grows to the surface produces roots. See also BBCH-scale (potato)

Hydrilla use stolons that produce tubers to spread themselves and survive dry periods in aquatic habitats.^[14]

Erythronium commonly called Trout Lily, have white stolons growing from the bulb. Most run horizontally, either underground or along the surface of the ground under leaf litter. Flowering plants often produce no stolons.^[15] A number of bulbous forming species produce stolons with Erythronium propullans producing one stolon below the soil surface on the midway point of the stem on blooming plants that produces a new bulb. On non blooming plants 1 to 3 stolons are produce directly from the bulbs, each ending in a new clone.^[16]

Convolvulus arvensis is a weed species in agriculture that spreads by under ground stolons that produce rhizomes.^[17]

In studies on grass species, with plants that produce stolons or rhizomes and plants that produce both stolons and rhizomes; morphological and physiological differences where noticed. Stolons have longer internodes and function as means of seeking out light and were used for propagation of the plant, while rhizomes are used as storage organs for carbohydrates and the maintenance of meristem tissue to keep the parent plant alive from one year to the next.^[18]

Mycology

In mycology, a stolon is defined as an occasionally septate hyphae, which connect sporangiophores together. Rootlike structures called rhizoids may appear on the stolon as well, anchoring the hyphae to the substrate. The stolon is commonly found in bread molds, and are seen as horizontally expanding across the mold.

See also

• Root
• Vegetative reproduction

References