Parenchyma are diverse cells and can have many different shapes and be very specialized in their function.

Cross section of plant cells.

Parenchyma cells are usually isodiametric or polyhedral in shape.

They have only a primary cell wall and retain the ability for future cell division.

Photo showing parenchyma cells.

Parenchyma cells contain a nucleus and when they are first formed, they are densely cytoplasmic and have several small vacuoles.

Photo of parenchyma cells pointing out cytoplasm and nucleus.

However, in older parenchyma cells the vacuoles merge into one large central vacuole with the cytoplasm and organelles - like these chloroplasts on the edges of the cell.

Photo of a cell pointing out the large central vacuole, with cytoplasm and chloroplasts along the edges.

Parenchyma are diverse cells and can have many different shapes and be very specialized in their function.

Based on their function specialized parenchyma cells can grouped as:

  • Ground tissue
  • Storage tissue
  • Chlorenchyma
  • Aerenchyma

Photo showing verious types of specialized cells.

The cortex and pith in stems and roots are parenchyma cells commonly referred to as the ground tissue.

The ground tissue surrounds the vascular system in the stem.

Photo of the cross-section of a plant stem, with the pith, cortex, and vascular bundles pointed out.-

Stem cross-section

There are several distinct storage tissues in plants. Three examples are:

  • Seed endosperm
  • Storage parenchyma
  • Ray parenchyma

Photo showing storage parenchyma in cotyledon.

Storage parenchyma in cotyledon.

The endosperm is designed to store food for the developing embryo and seedling.

Cross-section of a corn seed with the endosperm and embryo axis pointed out.

The endosperm is filled with lipid bodies, protein bodies and especially amyloplasts containing starch.

Photo pointing out protein bodies in legume endosperm.

Protein bodies in legume endosperm.

Photo pointing out amyloplasts in grain endosperm.

Amyloplasts in grain endosperm.

One of the major functions of parenchyma tissue is to store food reserves.

In some cases, large amounts of parenchyma are used for storage as in this beet root.

Photo of beet root cells showing parenchyma tissue.

A second major parenchyma type used for storage is ray parenchyma.

Ray parenchyma cells grow horizontal to the developing stem, sometimes deep within the non-living xylem cells.

Photo of ray parenchyma cells, pointing out rays and a dilated ray.

Ray cells are an important storage tissue to store carbohydrates and proteins over the winter in stems.

These stored materials are used to support new spring shoot and leaf growth.

Photo of plant cells pointing out ray cells.

Parenchyma cells in the leaf actively involved with photosynthesis are termed chlorenchyma.

Parenchyma cells pointing out chlorenchyma.

Chlorenchyma can be divided into the leaf palisade layer and the spongy mesophyll cells.

Cross-section photo of plant cells showing the leaf palisade layer and the mesophyll cells.

Illustration of plant material cross-section pointing out adaxial epidermis, palisade layer, mesophyll layer, and abaxial epidermis with stomate and guard cells.

The palisade layer is usually one to three cell layers deep and develops under the epidermis on the top (adaxial) side of the leaf.

Cross-section photo of plant material pointing out the palisade layer.

The spongy mesophyll cells occur below the palisade layer and are loosely packed together.

This creates air chambers that allows carbon dioxide to move from the stomata on the underside of the leaf to these chloroplast containing cells.

Cross-section photo of plant material pointing out mesophyll cells.

The leaf Palisade and Mesophyll cells contain abundant chloroplasts easily seen from the red color of chlorophyll in the leaf cross-section below.

Cross-section photo of plant cells, with chlorophyll artificially dyed red.

This electron micrograph shows a single mesophyll cell with an active nucleus and numerous chloroplasts.

Photo of a mesophyll cell with the nucleus and chloroplast pointed out.

Aerenchyma can occur in leaves, stems or roots and act as air passages.

They occur commonly in water logged roots and in aquatic plants.

Cross-section of a plant stem showing aerenchyma.

Aerenchyma is easily seen in the leaf of the floating water lily.

Air in arenchyma spaces help the leaf to float.

Leaf cross-section in Nymphaea (Water lily).

Leaf cross-section in Nymphaea (Water lily)

Aerenchyma can form from elongating cells creating large intercellular spaces or by cells disintegrating to leave a large air space.

Stem cross-section in Myriophyllum (Parrot feather).

Close up showing the aerenchyma of the Myriophyllum (Parrot feather).

Stem cross-section in Myriophyllum (Parrot feather)

Small cells form an intricate lattice structure creating aerenchyma in water hyacinth.

These air passages form pipes for air transport. However at intervals, cellular diaphragms form that allow air but not water to move through the passages.

This prevents sinking of this floating aquatic plant in case of damage that would allow water into the air passage.

Photo of plant cells pointing out lattice cells and diaphragm.

Lotus (Nelumbo) produces an edible root with large arenchyma spaces.

They help move air down into the submerged roots.

Photo of plant material with large arenchyma spaces.

Photo of sliced lotus root with large arenchyma spaces.