Cork-warts on the leaf epidermis of four genera of Celastroidea-Celastraceae

The presence of cork-warts on foliar lamina was first described at end of the 19th century, and since then these warts have been considered an additional taxonomic character for different taxa. In Celastraceae cork-warts have been reported so far only for the genus Euonymus. The objective of this study was to document the presence and morphology of cork-warts in Celastroideae-Celastraceae. The occurrence of cork-warts was investigated by paradermal and transversal views of the leaf epidermis of 15 species from five genera of the Celastroideae subfamily, using histological techniques and optical and scanning electron microscopy. The structures observed in paradermal view are characterized by suberin-incrusted areas forming layers of juxtaposed rectangular cells that originate through tangential divisions and form concentric structures. These structures were classified as either ordinary or stomatal cork-warts. Cork-warts are reported for the first time on Celastrus, Goniodiscus, Maytenus and Plenckia. Among the studied genera, only Fraunhofera lacked cork-warts.