leaf
The organ of a green plant specialized for photosynthesis. For this purpose leaves have a large surface area collectively, but species vary greatly in individual leaf shape, size and orientation. Many lower plants have much simpler laminar structures loosely called leaves, while the leaves of ferns are often called fronds. The leaves of vascular plants may be modified in various ways.
This definition is abridged from A – Z of tree terms: A companion to British arboriculture.
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