callus

noun

(L. callus, callum, hard skin) (pl. calluses) A hard protuberance or callosity; new tissue covering a wound. A protruding mass of hardened tissue, often formed after an injury but sometimes a regular feature of the plant, e.g. on the labellum of some orchids and the axis of the spikelet of some grasses. The thickened basal extension of the lemma in many grasses.