Profiles of the Headspace Volatile Organic and Essential Oil Compounds from the Tunisian Cardaria draba (L.) Desv. and Its Leaf and Stem Epidermal Micromorphology

In this work, we investigated aroma volatiles emanated by dry roots, stems, leaves, flowers, and fruits of Cardaria draba (L.) Desv. growing wild in Tunisia and its aerial part essential oils (EOs) composition. A total of 37 volatile organic compounds (96.7%–98.9%) were identified; 4 esters, 4 alcohols, 7 hydrocarbons, 12 aldehydes, 5 ketones, 1 lactone, 1 organosulfur compound, 2 organonitrogen compounds, and 1 acid. The hydrocarbons form the main group, representing 49.5%–84.6% of the total detected volatiles. The main constituent was 2,2,4,6,6-pentamethylheptane (44.5%–76.2%) reaching the highest relative percentages. Forty-two compounds were determined in the two fractions of EOs, representing 98.8% and 97.2% of the total oil composition, respectively. The principal components were hexadecanoic acid (34.6%), 6-methyl-5-hepten-2-one (18.3%), decanal (15.0%), 6,10,14-trimethyl-2-pentadecanone (13.2%), and n-pentacosane (13%). Micromorphological details of the leaf and stem epidermis using light microscopy revealed polygonal cells with sinuous walls in the adaxial and abaxial leaf surfaces and nearly rectangular and long ones with linear and thick walls for the stem epidermis. The stomata complexes were anisocytic in the leaf epidermis and mainly anisocytic and rarely paracytic in the stem epidermis. Non-glandular trichomes were unbranched and long with an acute apex or short with a convex apex. The glandular ones were identified for the first time in this species. They were short-stalked with a large secretory head. The highest stomatal index (17.02%) was recorded in the abaxial leaf surface. The identification of headspace volatiles and essential oil compounds can be used to characterize this species, and the various epidermis micromorphological features are very useful for biosystematics taxonomic studies within Brassicaceae.