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3.2.2: External Root Structure

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    Learning Objective

    Identify the types of root systems found in plants.

    There are two types of root systems. The first is a fibrous root system which has multiple big roots that branch and form a dense mass which does not have a visible primary root (“grass-like”). The other is the tap root system which has one main root that has branching into lateral roots (“carrot-like”).

    Root systems are mainly of two types (Figure \(\PageIndex{1}\)). Eudicots have a tap root system, while monocots have a fibrous root system. A tap root system has a main root that grows down vertically, and from which many smaller lateral roots arise. Dandelions are a good example; their tap roots usually break off when trying to pull these weeds, and they can regrow another shoot from the remaining root). A tap root system penetrates deep into the soil. In contrast, a fibrous root system is located closer to the soil surface, and forms a dense network of roots that also helps prevent soil erosion (lawn grasses are a good example, as are wheat, rice, and corn). Some plants have a combination of tap roots and fibrous roots. Plants that grow in dry areas often have deep root systems, whereas plants growing in areas with abundant water are likely to have shallower root systems.

    A carrots contains tap roots that have thin lateral roots extending from them. Fibrous root systems can be found beneath the soil.
    Figure \(\PageIndex{1}\): (a) Tap root systems have a main root that grows down, while (b) fibrous root systems consist of many small roots. (credit b: modification of work by “Austen Squarepants”/Flickr)

    Along with having different systems, there are primary root that originated from the root of the seedling (Figure \(\PageIndex{2a}\)) and secondary (lateral) roots originate from the primary roots, and adventitious roots originate on stems or leaves, rather than from the base of the embryo. Adventitious roots can grow if plant cuttings are placed in water (Figure \(\PageIndex{2b}\)).

    Wheat and Mung Bean seedlings, showing roots, stem, and cotyledonsJade plant cutting, showing adventitious roots growing from stem
    Figure \(\PageIndex{2}\): a) Mung bean tap root (eudicot) and wheat bean fibrous root (monocot) from sprouts. b) Jade plant cutting, showing adventitious roots growing from stem after being placed in water. Credit: Kammy Algiers (CC-BY).


    Curated and authored by Kammy Algiers using 5.5 The Root from Introduction to Botany by Alexey Shipunov (public domain)

    This page titled 3.2.2: External Root Structure is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Melissa Ha, Maria Morrow, & Kammy Algiers (ASCCC Open Educational Resources Initiative) .

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