Root System Modified Roots Function of Roots Characteristics of Roots Pictures of Roots The importance of trees Broadleaf and needleleaf trees

Most plants produce either a taproot system in which there is a single large root with smaller branch roots, or a fibrous root system in which there are many smaller roots of similar diameter. Some plants, however, have intriguing root modifications with specific functions in addition to those of anchorage and absorption. Explanation kinds of roots system. Aerial roots. Some plants, such as epiphytic orchids (orchids that are attached to tree branches and grow unconnected to the ground without being parasitic in any way) have roots that extend out into the air. Some aerial roots have an epidermis that is several cells thick, an adaptation to reduce water loss. These aerial roots may also be green and photosynthetic, as in the vanilla orchid. Some monocots, such as corn, produce thick roots from the lower parts of the stem; these prop roots grow down to the ground and brace the plants against wind. Explanation of the root system

Climbing plants such as ivy also produce roots from their stems; these anchor the stems to tree trunks or a brick wall. Any root that arises along a stem or in some place other than the root of the plant is called an adventitious root. Adventitious root formation in ivy depends on the developmental stage of the shoot. When the shoot transitions to the adult phase of development, it is no longer capable of initiating these roots. Explanation of the root system

Pneumatophores. Some plants that grow in swamps and other wet places may produce spongy outgrowths called pneumatophores from their underwater roots. The pneumatophores commonly extend several centimeters above water, facilitating the oxygen supply to the roots beneath. Explanation of the root system

Pneumatophores (foreground) are spongy outgrowths from the roots below.

Contractile roots. The roots from the bulbs of lilies and of several other plants such as dandelions contract by spiraling to pull the plant a little deeper into the soil each year until they reach an area of relatively stable temperatures. The roots may contract to a third of their original length as they spiral like a corkscrew due to cellular thickening and constricting. Explanation of the root system

Parasitic roots. The stems of certain plants that lack chlorophyll, such as dodder (Cuscuta), produce peglike roots called haustoria that penetrate the host plants around which they are twined. The haustoria establish contact with the conducting tissues of the host and effectively parasitize their host. Explanation of the root system

Food storage roots. The xylem of branch roots of sweet potatoes and similar plants produce at intervals many extra parenchyma cells that store large quantities of carbohydrates. Carrots, beets, parsnips, radishes, and turnips have combinations of stem and root that also function in food storage. Cross sections of these roots reveal multiple rings of secondary growth. Explanation of the root system

Water storage roots. Some members of the pumpkin family (Cucurbitaceae), especially those that grow in arid regions, may produce water-storage roots weighing 50 or more kilograms. Explanation of the root system

A water storage root weighing over 25 kilograms (60 pounds).

Buttress roots. Certain species of fig and other tropical trees produce huge buttress roots toward the base of the trunk, which provide considerable stability. Explanation of the root system

Buttress roots of a tropical fig tree.