30.4 VEGETATIVE REPRODUCTION

Eukaryotic organisms can reproduce asexually as well as sexually (Chapters 11 and 27). Asexual reproduction results in new individuals that are genetically identical to the parent. If the new individuals can disperse by walking, swimming, or floating away, asexual reproduction allows organisms to proliferate and spread.

In sexual reproduction, plants disperse by spores and seeds. What prevents asexually produced individuals from growing so close to the parent plant that they are in direct competition for resources? In mosses and liverworts, tiny plantlets form by mitosis at the base of shallow cups. Raindrops landing in this cup can dislodge the tiny plantlets, splashing some away from the parent plant.

Most plants that reproduce asexually do so by growing to a new location and only then producing a new plant. You need look no further than a front lawn to find evidence of such vegetative reproduction. Horizontal stems allow new upright grass shoots to be produced at a distance from the site where the parent plant originally germinated. Strawberries, bamboo, and spider plants (a common houseplant) also spread vegetatively by forming horizontal stems. In many cases, the connections that were needed initially to produce a new plant become severed. When this happens, only genetic evidence can be used to determine if a plant is the result of sexual or asexual reproduction.

Vegetative reproduction also occurs in woody plants. For example, when a redwood tree falls over, new upright stems can form along the now-horizontal trunk. Perhaps the most impressive example of the ability to spread vegetatively is the quaking aspen (Populus tremuloides), a common tree of the Rocky Mountains that produces brilliant yellow foliage in autumn (Fig. 30.24). Aspens reproduce vegetatively by producing upright stems from a spreading root system. Although each shoot lives for less than 200 years, a single individual can persist for tens of thousands of years by continuing to produce new stems. The current record holder is an aspen clone in Utah, consisting of nearly 50,000 stems, that is estimated to be 80,000 years old.

Plants are able to reproduce vegetatively because of how they build their bodies. As we will see in the next chapter, growth and development occur throughout a plant’s life, allowing plants to produce new upright “individuals” from roots or horizontal stems.