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In botany, the 'petiole' (from Latin ''peciolus'' "little foot," diminutive of ''pediculus'' "foot stalk," itself a diminutive of ''pes'' "foot") is the small stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the leaf. Clasping leaves of the Poaceae have an extra structure called the ligule.
'Phyllodes' are modified petioles. In some plants, the petioles become flattened and widened, while the leaf itself becomes reduced or vanishes altogether. Thus the phyllode comes to serve the purpose of the leaf. Phyllodes are common in the genus ''Acacia'', especially the Australian species, at one time put in ''Acacia'' subg. ''Phyllodineae''. Sometimes, especially on younger plants, partially formed phyllodes bearing reduced leaves can be seen.
The petiole allows partially submerged hydrophytes to have leaves floating at different depths. This enables photosynthesis to occur at the maximum rate.