A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants.
Typically a leaf is a thin, flattened organ borne above ground and specialized for photosynthesis, but many types of leaves are adapted in ways almost unrecognisable in those terms: some are not flat (for example many succulent leaves and conifers), some are not above ground (such as bulb scales), and some are without major photosynthetic function (consider for example cataphylls, spines, and cotyledons).
Conversely, many structures of non-vascular plants, or even of some lichens, which are not plants at all (in the sense of being members of the kingdom Plantae), do look and function much like leaves. Furthermore, several structures found in vascular plants look like leaves but are not actually leaves; they differ from leaves in their structures and origins. Examples include phyllodes, cladodes, and phylloclades.
Famous quotes containing the word leaf:
“With fairest flowers
Whilst summer lasts and I live here, Fidele,
Ill sweeten thy sad grave. Thou shalt not lack
The flower thats like thy face, pale primrose, nor
The azured harebell, like thy veins; no, nor
The leaf of eglantine, whom not to slander,
Outsweetened not thy breath.”
—William Shakespeare (15641616)
“I think that the leaf of a tree, the meanest insect on which we trample, are in themselves arguments more conclusive than any which can be adduced that some vast intellect animates Infinity.”
—Percy Bysshe Shelley (17921822)