Collenchyma are simple permanent tissue. It means they are composed of only one type of cells who have lost their ability to divide and have become specialised to perform specific functions.

Some of their features are as follows:

1. They consist of living cells which are somewhat elongated and appear circular, oval or polygonal in cross section.

2. They have thin cell wall but their corners are thickened due to deposition of pectin and cellulose.

3. They lack intercellular spaces and often contain chloroplasts.

Functions:

1. The provide mechanical strength and support to the plants and leaves. 

2. They can carry out photosynthesis if they contain chloroplasts.