Plant Life Cycles and Reproduction

Asexual Plant Reproduction

Asexual reproduction produces offspring plants that are genetically identical to the parent plant.

Asexual reproduction is a process of producing offspring that does not involve either meiotic cell division or syngamy, which is the fusion of two cells for reproduction. Asexual reproduction may occur when a plant is in the sporophyte stage (with two sets of chromosomes) or the gametophyte stage (with one set of chromosomes). The parent plants and daughter plants of asexual reproduction are genetically identical; the daughters are clones of the parent. Some plants, such as dandelions, reproduce seeds without undergoing meiosis. This process, called apomixis, is reproduction in which sexual organs take part but seeds form without union of gametes. Both flower-producing and nonflowering plants may reproduce asexually. Asexual reproduction occurs through a variety of mechanisms. The most common include vegetative propagation and apomixis. These mechanisms include stolons, rhizomes (underground horizontal roots), tubers, bulbs, or corms. A stolon is a shoot that grows along the ground and sends out roots from shoot nodes. A rhizome is an underground stem growing horizontally that sends roots down and plant shoots upward from a primary plant. Asexual reproduction in plants, such as stolons or by tubers, is called vegetative propagation.

Some plants reproduce by bulbs or corms. True bulb plants, such as daffodils and tulips, have a papery skin protecting the outer bulb. True bulbs are somewhat pear-shaped with internal layers of developing leaves and flowers that grow out of the top of the bulb. The bulb has a basal plate from which roots grow. A smaller offset bulb grows from the base and produces offspring through these daughter bulbs. Removed from the parent bulb, the offset bulb will grow a new daughter plant.

Corms are similar in shape to bulbs but have no layers inside. Corm tissue grows into stem, and the corm has a basal plate from which roots sprout. New corms, called cormels, form and grow to replace the parent plant. Cormels are the reproductive offspring of a corm. Crocus and gladiolus are corms and reproduce in this fashion.

Tubers are storage containers for plant carbohydrates. Potatoes and begonias are tubers, which produce roots that grow off a base root. With potatoes, each "eye" on a potato forms its own roots, the basis of the new potato plant.

Rhizomes are combinations of stem tissue and leaf tissue that may grow horizontally just beneath surface soil. Rhizomes send out shoots underground, and stems emerge as individual plants. This type of reproduction occurs with ginger, bamboo, poison oaks, and Bermuda grass. Aspen trees produce seeds and also reproduce by sending out rhizomes; an entire stand of aspens may all have been produced by a single parent tree.

Stolons, roots that spread out along the soil surface to produce new plants, are very similar to rhizomes. Often called runners, stolons have nodes and internodes. Each node produces a new plant; this means of propagating is common to spider plants and strawberries.

Apomixis in flowering plants occurs when the plant forms seeds in the ovule without undergoing meiosis and fertilization. Plants known to reproduce by apomixis include members of the aster family (asters, daisies, and sunflowers, among others), rosaceae (roses, blackberries, hawthorns, and apricots, among others), and poaceae (barley, grasses, millet, rye, and rice, among others). There are two main types of apomixes: gametophytic and sporophytic. With gametophytic apomixis, the seed originates in the mother cell (a megaspore) or begins from tissues in the egg cell. Sporophytic apomixis produces seed directly from tissues without producing an embryo sac.
Asexual reproduction, also called vegetative propagation, is a common mode of plant reproduction. It is often used in gardening and farming. For example, a stolon (runner) is one form of vegetative propagation where a root grows on top of the soil to allow for new plants to form.