A laterally flattened photosynthetic blade; for example, in many Australian Acacia, the expanded petiole, with the rachis and pinnae (of an otherwise bipinnate leaf) undeveloped or underdeveloped or falling early.
A leaflike petiole of a bladeless leaf, as in some Acacia.
A petiole that develops into a flattened expansion taking the place of a leaf.
A kind of leaf in which the blade has dwindled, in the evolutionary sense, to the point of being absent or almost absent, and the leaf stalk (petiole) has expanded to take over the leafs photosynthetic function. Many of the Australian species of Acacia are characterized by having phyllodes in the adult state, though their early seedling leaves are bipinnate.