Amount of calyx fibres in Lamiaceae, relation to calyx structure, phylogeny and ecology

Calyces of 306 species representing 181 out of the 236 genera of Lamiaceae have been studied with particular emphasis on the amount of fibres and similar xylem cells. 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. This result supports cladistic hypotheses based on cpDNA showing that Lamioideae and Scutellarioideae are closely related and remotely related to Nepetoideae. The new data also contribute to the knowledge about the phylogeny within Lamioideae. The amount of fibres and similar cells also seems to be positively correlated with calyx size, calyx width, a ballistic dispersal mechanism in Scutellaria, and the aridity of the habitat. Possible adaptive significances of these correlations are discussed.