A flattened stem resembling and functioning as a leaf WordNet 3.0 & Open English WordNet

Phylloclades and cladodes are flattened, photosynthetic shoots, which are usually considered to be modified branches. Wikipedia

A flattened organ arising from the stem of a plant. These often replace the leaves in photosynthetic function, as leaves in such plants (for example asparagus, butchers broom) are typically reduced to scales. The term may also refer to the generally flattened shoot such as the cactus shown. Wiktionary

Flattened organ. Wiktionary (translation)

A flattened stem, a type of cladode that has unlimited extension growth and resembles a leaf. Wiktionary