The Structure of a Typical Leaf

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 Illustration shows the parts of a leaf. The petiole is the stem of the leaf. The midrib is a vessel that extends from the petiole to the leaf tip. Veins branch from the midrib. The lamina is the wide, flat part of the leaf. The margin is the edge of the leaf.
Deceptively simple in appearance, a leaf is a highly efficient structure. Source: OpenStax Biology 2e

Biology Openstax 2e

Each leaf typically has a leaf blade called the lamina, which is also the widest part of the leaf. Some leaves are attached to the plant stem by a petiole. Leaves that do not have a petiole and are directly attached to the plant stem are called sessile leaves. Small green appendages usually found at the base of the petiole are known as stipules. Most leaves have a midrib, which travels the length of the leaf and branches to each side to produce veins of vascular tissue. The edge of the leaf is called the margin. The image above shows the structure of a typical eudicot leaf.

Within each leaf, the vascular tissue forms veins. The arrangement of veins in a leaf is called the venation pattern. Monocots and dicots differ in their patterns of venation. Monocots have parallel venation; the veins run in straight lines across the length of the leaf without converging at a point. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. One extant plant, the Ginkgo biloba, has dichotomous venation where the veins fork.

 Part A photo shows the broad, sword-shaped leaves of a tulip. Parallel veins run up the leaves. Part B photo shows a teardrop-shaped linden leaf that has veins radiating out from the midrib. Smaller veins radiate out from these. Right photo shows a fan-shaped ginkgo leaf, which has veins radiating out from the petiole.
(a) Tulip (Tulipa), a monocot, has leaves with parallel venation. The netlike venation in this (b) linden (Tilia cordata) leaf distinguishes it as a dicot. The (c) Ginkgo biloba tree has dichotomous venation. (credit a photo: modification of work by “Drewboy64”/Wikimedia Commons; credit b photo: modification of work by Roger Griffith; credit c photo: modification of work by “geishaboy500″/Flickr; credit abc illustrations: modification of work by Agnieszka Kwiecień) Source: OpenStax Biology 2e

Source:

Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/details/books/biology-2e

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