For all questions about leaves
Use this tag for all questions about leaves: e.g. possible diseases/symptoms, types of leaves, when they come out/fall, etc.
Leaves are the primary location for photosynthesis in almost all plants. They are usually flat and thin to maximize their surface area that is exposed to sunlight. Photosynthesis uses solar light radiation plus water (typically acquired via roots and carried by osmosis) and carbon dioxide (absorbed from the air), to produce sugars. This is used for energy but a plant also uses it to create starch and cellulose through polymerization (both are polymers of glucose).
Leaves have veins, which are the vascular tissue of the leaf:
- Xylem being water and minerals from the roots via osmosis
- Phloem move sap which carries dissolved sucrose out of the leaf
Leaf shapes can vary widely according to the plant's environment. For example, low-light conditions will tend to favor large leaves which try to catch as much light as possible. However, dry bright conditions will favor small leaves to minimize water loss.
Some leaves are edible by humans (e.g. the salads), although high cellulose content most other leaves (eg. grasses) mean special adaptations are often required in order to extract their full nutritional value (e.g. the multiple stomachs in an ungulate).
Bryophytes (mosses and liverworts) have flattened leaf-like structures but these are not considered true leaves by botanists because they are non-vascular (but still named leaves, or thallus or scale).
Ferns: the leaves are usually named frond.
On some plants, the leaves can be scales-like or needle-like.
Some plants have no leaves. Some of such plants have leaf-like stems, named cladodes (on this site we consider them as leaves), like in Ruscus aculeatus (butcher's-broom) or on asparagus.
Note: Many cacti have segments (so stems) and no foliage.