Origin:

• Parenchyma is derived from ground meristem
• Parenchyma present in vascular tissues is formed from procambium and vascular cambium.

It is most primitive, commonest, simplest, most abundant, unspecialized type of permanent tissue.Remaining all different types of tissue is derived from this tissue. So it also called as fundamental tissue.

Characteristic features:

• It is a living tissue.

• It is universal in presence, found in all softer and non-woody plant parts (ex, root, stem and leaf) and all plant.
• All the cells of parenchyma are thin walled, both primary and secondary walls are found generally made up of pectocellulose.
• Parenchyma is most common tissue which is morphologically and physiologically unspecialized.
• Each cell containing large central vacuole.
• Inter cellular spaces are well developed between cells. These are schizogenous in origin

Shape:

• The cells are isodiametric (all sides equal) which may be oval, round, polygonal, elongated etc.
• Each parenchymatous cell is composed by planes of 14 lateral lines. These are known as tetrakaidecahedron. This characteristic of cells is due to more flexibility.

Modifications: 

1. Prosenchyma

• The cells of this parenchyma are long, elongated fibre like structure with thick wall pointed ends. 
• This parenchyma forms pericycle of roots. 

2.Aerenchyma

• This parenchyma is made up of rounded cells.
• These cells contain the large air cavities.
• Present in hydrophyte plants and provides buoyancy to plants.

3. Stellate parenchyma:

• Air spaces are also present but they are less developed.
• Main function of this parenchyma is to provide buoyancy to plant.
  
• These tissues are found in leaf bases of Banana.
• It provide strength to leaf bases. Leaf base of Banana perform the functions of stem.
• The cells of this tissue are stellate and branched.

4. Chlroenchyma

• Abundant quantity of chloroplasts are foundin these parenchymatous cells.
  
• Two types tissue formed bychlorenchma cells are present in dorso-ventral leaves.

a. Palisade tissue:

• This lack inter cellular spaces.
  
• Their cells are tightly fitted together.
  
• They are present at adaxial/ventral/upper side of leaf.
  
• Number of chloroplasts are more in cells of palisade tissue as compare to spongy tissue.
  

b. Spongy tissue

• Spongy tissue contains large intercellular spaces.
  
• They are present at abaxial /dorsal/lower side of leaf.
  

5. Mucilage Parenchyma:

• Large vacuoles and Mucilage are found in these parenchymatous cells.
  
• Functions as storage of water and mucilage. e.g. Succulent xerophytic plants, Aloeetc

Functions of parenchyma:

1. The main function of this tissue is storage of food.
2. Some cells of parenchyma store waste materials.
3. They are called "Idioblast cells" Idioblast cells stores oils, tannin and crystal of calcium oxalates in the form of food.