Leaf

A leaf is a plant organ specialized chiefly for photosynthesis, gas exchange, and water loss. Its shape and internal tissues support these functions in diverse environments.

Mesophyll: The internal leaf tissue where most photosynthesis occurs. Its cells contain chloroplasts that capture light and fix carbon.
Leaf blade: The broad, usually flattened portion of a leaf. Its exposed surface captures light and exchanges gases.
Phyllotaxis: The arrangement of leaves around a plant stem. Leaf spacing can reduce shading and improve light interception.
Needle (botany): A narrow, often evergreen leaf characteristic of many conifers. Needles reduce exposed surface area compared with broad leaves.
Stoma: A microscopic pore in a plant surface, controlled by surrounding guard cells. Stomata admit carbon dioxide while regulating water loss.
Petiole: The stalk that connects a leaf blade to a stem. It positions the blade and joins its vascular supply to the stem.
Leaf area index: The amount of leaf area per unit of ground area in a vegetation canopy. It estimates how strongly a canopy intercepts light and exchanges gases.
Succulent leaf: A thick, water-storing leaf adapted to dry conditions. Its water storage contrasts with thin leaves that lose water rapidly.
Guard cell: A specialized epidermal cell that opens or closes a plant stoma. Guard cells adjust pore width as light, water, and carbon dioxide conditions change.
Leaf venation: The arrangement of veins within a leaf blade. Veins distribute water and collect sugars across the blade.

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