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Biology LibreTexts

30.3B: Root Modifications

  • Page ID
    13751
  • Plants have a wide variety of roots for functions as diverse as structural support, food storage, and parasitism.

    LEARNING OBJECTIVES

    Explain the reasons for root modifications

    KEY TAKEAWAYS

    Key Points

    • Storage roots, which include a large number of edible vegetables such as potatoes and carrots, are some of the most commonly-known types of modified roots.
    • Aerial roots encompass a variety of shapes, yet function similarly as structural support for the plant.
    • Parasitic plants have special haustorial roots that allow the plant to absorb nutrients from a host plant.

    Key Terms

    • succulent: having fleshy leaves or other tissues that store water
    • epiphyte: a plant that grows on another, using it as a physical support but neither obtaining nutrients from it nor causing it any damage if also offering no benefit

    Root Modifications

    Plants have different root structures for specific purposes. There are many different types of specialized roots, but two of the more familiar types of roots include aerial roots and storage roots. Aerial roots grow above the ground, typically providing structural support. Storage roots (for example, taproots and tuberous roots) are modified for food storage.

    Aerial roots are found in many different kinds of plants, offering varying functions depending on the location of the plant. Epiphytic roots are a type of aerial root that enable a plant to grow on another plant in a non-parasitic manner. The banyan tree begins as an epiphyte, germinating in the branches of a host tree. Aerial prop roots develop from the branches and eventually reach the ground, providing additional support. Over time, many roots will come together to form what appears to be a trunk. The epiphytic roots of orchids develop a spongy tissue to absorb moisture and nutrients from any organic material on their roots. In screwpine, a palm-like tree that grows in sandy tropical soils, aerial roots develop to provide additional support that help the tree remain upright in shifting sand and water conditions.

    image

    Aerial roots: The (a) banyan tree, also known as the strangler fig, begins life as an epiphyte in a host tree. Aerial roots extend to the ground, supporting the growing plant, which eventually strangles the host tree. The (b) screwpine develops aerial roots that help support the plant in sandy soils.

    Storage roots, such as carrots, beets, and sweet potatoes, are examples of roots that are specially modified for storage of starch and water. They usually grow underground as protection from plant-eating animals. Some plants, however, such as leaf succulents and cacti, store energy in their leaves and stems, respectively, instead of in their roots.

    image

    Storage roots: Many vegetables, such as carrots and beets, are modified roots that store food and water.

    Other examples of modified roots are aerating roots and haustorial roots. Aerating roots, which rise above the ground, especially above water, are commonly seen in mangrove forests that grow along salt water coastlines. Haustorial roots are often seen in parasitic plants such as mistletoe. Their roots allow the plants to absorb water and nutrients from other plants.

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