A cardinal organ part (PO:0025001) at the apex or base of a petiole, petiolule, leaf sheath, or branch that is differentiated from the remaining organ parts by its enlarged cross section. [source: POC:curators]
Often glandular. Often involved in movement of a plant structure in response to touch, gravity or light. In panicoid grasses a swollen region in the stem above the intercalary meristem. Such a definition would also include stems of Chloranthaceae, Acanthaceae, Carpels, Amaranthaceae, etc. [source: APweb:Glossary].