Structural and Chemical Adaptations of Artemisia monosperma Delile and Limbarda crithmoides (L.) Dumort. in Response to Arid Coastal Environments along the Mediterranean Coast of Egypt

Arid coastal habitats are stressful regions subjected to the effects of biotic and abiotic factors. Vascular plants in these habitats display different responses to cope with these environmental fluctuations. This work addressed the morpho-anatomical features and chemical responses of two medicinal vascular plant species Artemisia monosperma Delile and Limbarda crithmoides (L.) Dumort., growing naturally along the Mediterranean coast of Egypt. Soil properties (physical and chemical), morpho-anatomical features and chemical constituents (secondary metabolites, antioxidant activity and essential oils) for the two species were performed. Our results displayed that both species are surviving where soils are alkaline, high saline with low moisture and organic carbon. The morphology of both species appeared woody low shrub with fleshy leaves. The most marked anatomical attributes were the thick cuticle of the epidermal layer in leaves and stems, compact palisade cells and abundant idioblasts (secretory ducts, phenolic compounds and calcium oxalate). Also, sclerenchymatous pericycle fibers in stem and glandular trichomes on the leaf had appeared in A. monosperma. Both plants exhibited a considerable content of phenolics, flavonoids, tannins, alkaloids and antioxidant activity with a higher level in A. monosperma than L. crithmoides. The leaf extracts of both plants showed higher values than the stem extracts. The sesquiterpenes group were the major identified compounds of the essential oils (EOs) in A. monosperma and L. crithmoides, and the majority were oxygenated sesquiterpenes with percentages of 42.63% and 51.49%, respectively. The second major group of EOs was monoterpenes, which were represented in A. monosperma in concentrations (34.04%) much higher than those recorded in L. crithmoides (4.97%). Exploring the local adaptation mechanism used by the target plants helps us to understand how these plants can acclimatize to harsh conditions, and this provides critical insights into the protection and survival strategy of species under extreme conditions.