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13.4: Modified Leaves

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    The structure and function of a leaf can be modified over the course of evolution as a plant adapts to a particular environment. Some leaves may be converted to storage structures below ground (as with a bulb) or into plant defense structures (as with a spine). When function of the leaf blade is no longer primarily photosynthesis, some other plant part is usually modified to take its place. A phyllode is a petiole that has become flat and photosynthetic, looking much like a leaf blade.

    Examples of leaf modifications. A single leaf has been filled in on each of the four examples.
    Figure \(\PageIndex{1}\): A diagram of leaf modifications. In each plant (A-D), one leaf has been shaded with orange. In A, the blade has been modified for a trap, the petiole is flattened into a phyllode. In B, the blade is a compound leaf and the petiole is flattened into a phyllode. In C, some of the leaves are tendrils (emerging below axillary buds). In D, the basal leaves are thick and fleshy with a short stem (a bulb). Diagram by Nikki Harris, CC-BY 4.0 with labels and color added by Maria Morrow.

    Bulb

    An onion bulb cut longitudinally has a small stem and layers of thick, fleshy leaves.
    Figure \(\PageIndex{2}\): The onion bulb has a relatively small stem (tan tissue just above the roots) surrounded by thick, fleshy leaves. Image by JonRichfield (CC-BY-SA).

    Succulent

    A plant viewed from the top with succulent leaves. The leaves are thicker than normal leaves.
    Figure \(\PageIndex{3}\): Succulent leaves are thickened for water storage. This water-storing tissue is called hydrenchyma (see Figure \(\PageIndex{4}\), bottom). Photo by Simon Burchell, CC BY-SA 4.0, via Wikimedia Commons.

    Succulent leaves of Guzmania lingulata

    Sections of leaves of G. lingulata showing hydrenchyma
    Figure \(\PageIndex{4}\): Top: "(A) Plants of Guzmania lingulata in the field at La Selva biological Station, Costa Rica, and (B) a single leaf of G. lingulata labeled with the two leaf regions examined." Bottom: "Sections of leaves of G. lingulata used to measure anatomical traits. Leaf clearings of the leaf blade (A) and tank region (B) used to determine interveinal distance (Div; black arrow); scale bars in (A) and (B) = 500 μm. Cross-sections of the leaf blade (C) and tank region (D); red lines indicate pathways for water between vein and abaxial surface (red line in (C) used to calculate Dmes; black arrow indicates distance between vein and epidermis Depi); scale bars in (C) and (D) = 50 μm. Abbreviations: bundle sheath cells (bs), hydrenchyma (hyd), mesophyll (mes), stomate (sto), and trichome (tri)." Figures and caption text from Leaf Hydraulic Conductance for a Tank Bromeliad: Axial and Radial Pathways for Moving and Conserving Water, North et al. 2013. Creative Commons Attribution 3.0 Unported.

    Tendril

    Vining pea-type plants with compound leaves. A compound leaf with three long thin projections at the end instead of blades.
    Figure \(\PageIndex{5}\): Many plants in the bean family (Fabaceae) produce leaf tendrils where all or part of the leaf forms a tendril. The first image is an illustration of a plant with compound leaves, some of the leaflets forming tendrils. The second image is of Vicia villosa with the terminal leaflets forming three tendrils. First image from Elsie Garrett Rice, Public domain, via Wikimedia Commons. Second image from Harry Rose from South West Rocks, Australia, CC BY 2.0, via Wikimedia Commons.
    A wide leaf blade with a tip that extends into a tendril curling around an adjacent stem
    Figure \(\PageIndex{6}\): "Leaf tendrils: In weak-stemmed plants, leaf or a part of leaf gets modified into tendrils i.e., a green coiled threadlike structure which helps in climbing around the support. Gloriosa or Glory Lily has leaf tip modified into tendrils." Image and caption text by Krishna satya 333, CC BY-SA 4.0, via Wikimedia Commons.

    Spine

    Several spines from a cactus.
    Figure \(\PageIndex{7}\): Cactus spines are not stems, but modified leaves. These spines have a thick cuticle and stomata can be seen as darker green areas within the pale white cuticle. Photo by André Karwath aka Aka, CC BY-SA 2.5, via Wikimedia Commons.
    A branch with numerous sharp spines. At the base of each spine there is an axillary bud.
    Figure \(\PageIndex{8}\): Ocotillo leaf petioles form into spines. Note the axillary buds present in the axil of each spine. Photographed by and copyright of (c) David Corby (User:Miskatonic, uploader) 2006. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.
    Woody branches with small, newly budding leaves. Each leaf has two large, woody spikes emerging from the base.
    Figure \(\PageIndex{9}\): Stipular spines of an Acacia sp. The paired sharp armaments subtend the leaves on this woody shrub. Dr Mary Gillham Archive Project, CC BY 2.0, via Wikimedia Commons.

    Traps

    Dionaea (venus fly trap) leaf trap and phyllode, labeled Nepenthes (a pitcher plant) leaf trap, tendril, and phyllode, labeled

    Modified leaves of a Venus flytrap and pitcher plant
    Figure \(\PageIndex{10}\): The (a) Venus flytrap has modified leaves that can capture insects. When an unlucky insect touches the trigger hairs inside the leaf, the trap suddenly closes. The opening of the (b) pitcher plant is lined with a slippery wax. Insects crawling on the lip slip and fall into a pool of water in the bottom of the pitcher, where they are digested by bacteria. The plant then absorbs the smaller molecules. Top two photos by Maria Morrow, CC-BY 4.0. Last two photos credit a: modification of work by Peter Shanks; credit b: modification of work by Tim Mansfield, adapted from Botany by Algiers, Ha, and Morrow.
    Drosera (sundew) with glandular trichomes to trap insects
    Figure \(\PageIndex{11}\): The ends of sundew (Drosera sp.) leaves are covered with glandular trichomes. Each trichome has a blob of sticky fluid at the tip. Insects are attracted to the fluid, becoming trapped in it, and the plant can slowly digest their bodies for the mineral nutrients that are lacking in their environment. Photo by Maria Morrow, CC-BY 4.0.

    This page titled 13.4: Modified Leaves is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Maria Morrow (ASCCC Open Educational Resources Initiative) .

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