In leaves, the ground tissue is called mesophyll.

• Mesophyll is the tissue between the upper and lower epidermis of a leaf.
• It is primarily composed of parenchyma cells, which are responsible for photosynthesis.
• There are two types of mesophyll cells:
  • Palisade mesophyll: These are elongated cells located directly below the upper epidermis, containing many chloroplasts for efficient light capture.
  • Spongy mesophyll: These are irregularly shaped cells with large air spaces between them, which facilitate gas exchange (CO2 uptake and O2 release).

Source: BioLibreTexts - Leaf Mesophyll