Extensive investigations on the anatomy of the two leaf types in a seasonally dimorphic subshrub revealed interesting variations between summer and winter leaves. Summer leaves of Sarcopoterium spinosum possess a thick epidermis composed of tannin-containing cells and large amounts of mucilage secreted through the inner periclinal walls towards the mesophyll. A thick cuticle is also present on the surface of the leaf. In winter leaves the epidermal cells produce no mucilage while phenolics are accumulated in granular form only. Besides these, some other variations between summer and winter leaves are also discussed in respect of the ability of the plant to withstand the unfavourable Mediterranean conditions. © 1990 Annals of Botany Company.