I read in my biology textbook that ground tissue is constituted by parenchyma, collenchyma and sclerenchyma.It was also mentioned that, in leaves the ground tissue was made up of thin walled chloroplast containing cells called mesophyll cells.
Despite countless sites and other resources saying otherwise, Mesophyll is not a tissue technically speaking. It's just a place, a specific area. Or you can even think of it as the set of all tissues in a given area.
And that given area is easy to define: the "filling" of the leaf, between the upper and lower epidermis. According to Mauseth (2012), that with Raven is my favourite book on Botany:
Mesophyll: All tissues of a leaf except the epidermis.
Actually, this is easy to see if you understand the Greek origin of the term: μέσος, meaning "in the middle", and φύλλον, meaning "leaf". Therefore, mesophyll means "in the middle of the leaf".
In a common, regular leaf, most of the mesophyll is made of parenchyma, be it palisade or spongy. As I said before several sources treat these terms (mesophyll and parenchyma) as synonyms, but they are not.
Just for completeness, this is a very simple list of the plant tissues. You'll see that mesophyll is not on it:
- Dermal tissues
- Ground tissues
- Vascular tissues
Source: Mauseth, J. (2012). Botany. Sudbury: Jones & Bartlett Learning.