Parenchyma is not much differentiated and is composed of cells with a thin primary cellulosic wall. Intercellular spaces are observed varying in size from small to large (lacuna) according to the kind of parenchyma. Parenchyma cells are often polyhedral or elongate. The form, the volume and the thickness of an organ (during its primary growth) generally results from the development of parenchyma. Parenchyma is present in all plant organs and have important functions: photosynthesis (leaves and stems), storage of different molecules (seeds, roots, tubers), perception of gravity (root and stem), adaptation to environments.
Mature parenchyma cells of stem and root may resume division and undergo partial dedifferentiation to form lateral meristems. They can regenerate parts of the plant or the entire plant in appropriate conditions. This property called “totipotency” is exploited in in vitro propagation of plants.
Based on their function 4 different types of parenchyma can be distinguished. Micrographs are shown on this website to illustrate the different types:
1/ Photosynthetic parenchyma also called chlorenchyma Example: leaves and stems in Arabidopsis thaliana. See also :leaf anatomy.
2/ Storage parenchyma which synthetize and store different substances. The most frequent storage molecule is starch. Example: starch parenchyma in potato chair and in endosperm of mays caryopsis.
3/ “Aquiferous” parenchyma typical of plants that live in dry environments, plants known as xerophytes (sclerophytes and succulent). They store water in their vacuoles. Example: Aloe arborescens.
4/ “Aeriferous” parenchyma called “aerenchyma”, a well-developed tissue in plants living in wet or aquatic environments, plants known as hydrophytes. The aerenchyma is characterized by large interconnected empty intercellular spaces, where gases can diffuse and aerate the organ. We find it in the different organs : leaves (Examples: Eichornia crassipes, Typhonodorum lindleyanum); petioles; in stems and in roots such as Ranunculus and Nymphea
In plants living in particular conditions such as border of ocean, parenchyma is mostly lignified. Example: Psamma arenaria leaf, a xerophyte.
The central part of root cap, the columella region, consists of parenchyma, with cells called statocyst that contain statoliths responsible for gravity perception of roots.