Calcium Oxalate Cuticular Crystals in the Epidermis of Dracaena—A Taxonomic Feature of the Genus

Abstract

The genus Dracaena has been placed in Agavaceae by most taxonomists. Recent work, however, has justified the placement in a separate family, Dracaenaceae. This study was initiated to examine the extracellular crystalline deposits in Dracaena and the possibility of this feature as a taxonomic trait of the genus. Fresh epidermal peels of five Dracaena species were observed under polarized light. Extracellular epidermal crystals were evident in all of them. The deposits were found between the cuticle and the outer primary epidermal cell wall. The crystal size varied from less than 1 μm to 5 μm along the long crystal axis. The size and quantity of the deposits varied between the species with largest and most numerous crystals in the cuticle of D. marginata and D. sanderiana. Dracaena deremensis, D. fragrans, and D. surculosa had smaller and less numerous crystals. The optical properties of the crystals were indicative of calcium oxalate monohydrate form which exhibited interference colors of second and third order. For comparison species of three members of Agavaceae were examined -Cordyline terminalis, Sansevieria trifasciata, and Yucca sp. No extracellular crystal deposits in the proximity of the epidermal wall were detected. Based on our observations, the genus Dracaena possessed an anatomical feature which could be used for identification. The existence of calcium oxalate crystals embedded in the cuticle was readily observable in fresh epidermal peels under polarized light.