noun, plural: phyllodia
(1) A modified petiole in some plants in which the petiole is characteristically flattened resembling and performing functions similar to a true leaf, even replacing the true leaves as major photosynthetic structure in certain plant groups.
In flowering plants, a petiole is generally slender and chiefly renders support by attaching the leaf blade to the stem. In some plants, the petioles become modified or specialized in a way that they become leaf-like in appearance (expanded) and serve not only to support the leaf but to carry out photosynthesis as well. An example is the acacia. The phyllodes of Acacia koa for instance are thick and coriaceous helping the plant in surviving stressful environment.
Word origin: from New Latin phyllodium, from Greek phullōdēs (leaflike)