A caudex (plural: caudices) of a plant is a stem, but the term is also used to mean a rootstock and particularly a basal stem structure from which new growth arises.
The caudex of a tree fern resembles the trunk of a woody plant
, but has a different structure.
In the strict sense of the term, meaning a stem, "caudex" is most often used with plants that have a different stem morphology from the typical angiosperm dicotyledon stem: examples of this include palms, ferns, and cycads.
The related term caudiciform, literally meaning stem-like, is sometimes used to mean pachycaul, thick-stemmed.