Calyces of c. 410 species representing 182 out of the 236 genera of Lamiaceae have been studied with particular emphasis on the amount of fibres and crystals. A characteristic calyx tissue called "mesophyll fibres", reported by earlier authors, is found to belong to the xylem. Most species of the subfamilies Lamioideae and Scutellarioideae differ from most other labiates, and particularly from Nepetoideae, in having much larger amounts of fibres and similar xylem cells in the calyx tube. The new data contributes to the knowledge about the phylogeny within Lamioideae. Many members of the subfamily Nepetoideae are found to have prismatic crystals in the inner epidermis, while this type of crystals lack in the other subfamilies. The amount of fibres and similar cells are found to be particularly common in closed calyces. Their position in the calyces suggests that both fibres and crystals have a protective function. Fibres are also associated to a ballistic dispersal mechanism in Scutellaria.