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 leaves:
“What is a country without rabbits and partridges? They are among the most simple and indigenous animal products; ancient and venerable families known to antiquity as to modern times; of the very hue and substance of Nature, nearest allied to leaves and to the ground,and to one another; it is either winged or it is legged. It is hardly as if you had seen a wild creature when a rabbit or a partridge bursts away, only a natural one, as much to be expected as rustling leaves.”
—Henry David Thoreau (18171862)
“Beware the politically obsessed. They are often bright and interesting, but they have something missing in their natures; there is a hole, an empty place, and they use politics to fill it up. It leaves them somehow misshapen.”
—Peggy Noonan (b. 1950)
“Gentleman. A man who buys two of the same morning paper from the doorman of his favorite nightclub when he leaves with his girl.”
—Marlene Dietrich (19041992)