In botany, a cortex is an outer layer of a stem or root in a

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

, lying below the epidermis but outside of the

vascular bundle A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in the stem, which exists in two forms: xylem and phloem. Both these tissues are present in a vascular bundle, which in addition will inc ...

s. The cortex is composed mostly of large thin-walled parenchyma cells of the

ground tissue The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. # Parenchyma cells have thin primary walls and usually remain alive after they beco ...

system and shows little to no structural differentiation. The outer cortical cells often acquire irregularly thickened cell walls, and are called

collenchyma The ground tissue of plants includes all tissues that are neither dermal nor vascular. It can be divided into three types based on the nature of the cell walls. # Parenchyma cells have thin primary walls and usually remain alive after they bec ...

cells.

Plants

Stems and branches

In the three dimensional structure of herbaceous stems, the epidermis, cortex and

vascular cambium The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xy ...

form concentric cylinders around the inner cylindrical core of

pith Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In eudicotyledons, pith is located in the center of the stem. In monocotyledons, it ext ...

. Some of the outer cortical cells may contain chloroplasts, giving them a green color. They can therefore produce simple carbohydrates through photosynthesis. In woody plants, the cortex is located between the

periderm Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consist ...

(bark) and the vascular tissue (

phloem Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...

, in particular). It is responsible for the transportation of materials into the central cylinder of the root through diffusion and may also be used for storage of food in the form of starch.

Roots

In the roots of vascular plants, the cortex occupies a larger portion of the organ’s volume than in herbaceous stems. The loosely packed cells of root cortex allow movement of water and oxygen in the intercellular spaces. One of the main functions of the root cortex is to serve as a storage area for reserve foods. The innermost layer of the cortex in the roots of vascular plants is the

endodermis The endodermis is the central, innermost layer of cortex in land plants. It is a cylinder of compact living cells, the radial walls of which are impregnated with hydrophobic substances (Casparian strip) to restrict apoplastic flow of water to th ...

. The endodermis is responsible for storing starch as well as regulating the transport of water, ions and plant hormones.

Lichen

On a lichen, the cortex is also the surface layer or "skin" of the nonfruiting part of the body of some lichens.What is a lichen?, Australian National Botanical Garden
/ref> It is the "

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

", or outer layer of

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

tissue, that covers the undifferentiated cells of the

medulla Medulla or Medullary may refer to: Science * Medulla oblongata, a part of the brain stem * Renal medulla, a part of the kidney * Adrenal medulla, a part of the adrenal gland * Medulla of ovary, a stroma in the center of the ovary * Medulla of t ...

Fruticose A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or ...

lichens have one cortex encircling the branches, even flattened, leaf-like forms;

foliose Foliose lichen is one of the morphological classes of lichens, which are complex organisms that arise from the symbiotic relationship between fungi and a photosynthetic partner, typically algae. This partnership allows lichen to live in diverse ...

lichens have different upper and lower cortices;

crustose Crustose is a habit of some types of algae and lichens in which the organism grows tightly appressed to a substrate, forming a biological layer. ''Crustose'' adheres very closely to the substrates at all points. ''Crustose'' is found on rocks ...

, placodioid, and

squamulose A squamulose lichen is a lichen that is composed of small, often overlapping "scales" called squamules. If they are raised from the substrate and appear leafy, the lichen may appear to be a foliose lichen, but the underside does not have a "ski ...

lichens have an upper cortex but no lower cortex; and leprose lichens lack any cortex.

References

{{DEFAULTSORT:Cortex (Botany) Plant anatomy Plant physiology

Plants

Stems and branches

Roots

Lichen

See also

References