In plant
terminology, a petiole is the base of the leaf, which connects the '
blade' (the 'leafy' part) to the stem. The petiole is considered to be part of the
leaf. Petioles come in many forms - some are almost absent, others are quite large. In a
compound leaf, the petiole may branch and bear many leaf blades. In some cases, it is quite hard to tell a petiole from a stem. Generally, they are flatter than regular stems, and green, but this is not always true. Also, in
deciduous plants, the petiole falls off along with the blade of the leaf. But the only sure sign of where a petiole ends and a leaf begins is the small axial bud which is found at the base of a petiole, above it on the stem. Junctions of 'stems' adjacent to the leaf which lack this are probably just forks in the petiole.
One example of a plant with dominant petioles which look like leaves is heavenly bamboo. In the case of this plant, most of the 'stems' other than the main stems are petioles.