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3.4: Leaves

  • Page ID
    27737
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    Leaves are specialized organs of the shoot for performing photosynthesis. A leaf is often a relatively large, flat surface used to optimize sunlight capture. Most leaves have determinate growth, meaning that growth stops once the leaf reaches a certain size. This is in contrast to the overall plant body, which grows indeterminately. Leaves arise from the shoot apical meristem through leaf primordia.

    Usually, true leaves are easily distinguishable, but in some species, modified stems (cladophylls and phyloclades) or leaflets (parts of leaves) superficially appear like whole leaves. True leaves subtend an axillary bud in the axil and are lateral (rather than at the tip, or apex of the shoot; Figure \(\PageIndex{1}\)). New shoots and leaves do not arise from true leaves.

    A potted plant with the root system, shoot system, and organs labeled.
    Figure \(\PageIndex{1}\): Leaves are lateral structures of the shoot system. The plant here is divided into a generative shoot system, vegetative shoot system, and root system. The generative shoot system consists of the floral unit, which is supported by the pedicel. The vegetative shoot system consists of stems and leaves. Leaves attach at nodes on the main stem. Stem segments between nodes are internodes. Leaves consist of a flattened blade and stalklike petiole, and they subtend axillary buds (labeled axial bud here). Some axillary buds have developed into secondary shoots. Terminal (apical) buds are found at the end of stems. In the root system, lateral roots arise from the main root (taproot). Adventitious roots arise from the stem. At the base of the main stem, just before it transitions to the main root is the hypocotyl.

    Most leaves are usually green, due to the presence of chlorophyll in the chloroplasts of their cells. However, some leaves may have different colors, caused by other plant pigments that mask the green chlorophyll. The thickness, shape, and size of leaves are adapted to the environment. Each variation helps a plant species maximize its chances of survival in a particular habitat.

    Attributions

    Curated and authored by Melissa Ha using the following sources:

    Thumbnail image: The red petal-like structures of the poinsettia plant are actually modified leaves called bracts, which are adapted to attract pollinators. The true flowers tiny structures where the bracts meet. Image by Scott Bauer (public domain).


    This page titled 3.4: Leaves 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) .