The plant cortex is far more than just a simple layer of cells.

Health · Published 3 October 2026 Swipe more like this →

In short: Tucked between a plant's outer skin and its internal plumbing lies the cortex, a versatile tissue that does everything from storing starch to powering photosynthesis. Far from being a passive filler, this unspecialized layer acts as a critical regulator of water, air, and energy for the plant's survival.

In vascular plants, the cortex serves as a fundamental structural component, occupying the space between the epidermis and the vascular bundles. Composed primarily of parenchyma cells, this tissue is remarkably adaptable. In herbaceous stems and succulents, cortical cells contain chloroplasts, allowing them to perform photosynthesis and convert carbon dioxide into carbohydrates. These simple sugars are often metabolized into starch, which the plant then stores within the cortex of roots, bulbs, and tubers for later use.

Beyond storage and energy production, the cortex plays a vital role in internal transport. In roots, the innermost layer of the cortex, known as the endodermis, acts as a gatekeeper. It features a specialized band called the casparian strip, which helps regulate the flow of water, ions, and hormones between the outer tissues and the plant's central vascular cylinder. In some species, the cortex can even develop into aerenchyma, a tissue characterized by air spaces that facilitate the movement of oxygen and water.

The term also extends to the world of lichens, where it describes the protective skin of the thallus. Depending on the lichen's growth form—whether fruticose, foliose, or crustose—the cortex may cover the entire body or only the upper surface, shielding the internal medulla. While the botanical cortex in plants is defined by its position relative to vascular tissues, the lichen cortex serves as a distinct morphological boundary, demonstrating how the same biological term can describe specialized protective layers across different life forms.

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