In
biology, a
tunica (plural
tunicae) is a layer, coat, sheath, or similar covering. The word came to English from the
New Latin of science and medicine. Its literal
sense is about the same as that of the word
tunic, with which it is
cognate. In biology one of its senses used to be the
taxonomic name of a
genus of plants, but the nomenclature has been revised and those plants are now included in the genus
Petrorhagia.