Leaf Anatomy and Modifications

Pair of cells regulating stomatal opening and closure

Guard cells

Epidermal cells that assist guard cells when present

Subsidiary cells

Photosynthetic ground tissue between the upper and lower leaf epidermis

Mesophyll

Dense, elongated photosynthetic cells often beneath the upper epidermis

Palisade mesophyll

Loose photosynthetic tissue with air spaces for internal gas diffusion

Spongy mesophyll

Grass-leaf epidermal cells involved in leaf rolling under water stress

Bulliform cells

Modified leaf with a sharp protective tip, as in cactus

Leaf spine

Sharp defensive structure derived from a stem or branch, not a leaf

Thorn

Sharp outgrowth of epidermal and superficial cortical tissue

Prickle

Flattened photosynthetic petiole or rachis replacing a normal leaf blade

Phyllode

False stem of banana formed mainly from overlapping leaf sheaths

Pseudostem