Leaf Structures of Xerohalophytes from an East Jordanian Salt Pan

Abstract

Leaves from 13 perennial halophytes growing in typical zonations along a vegetational transect were comparatively studied for their morphological-anatomical features. With SEM, curvatures of the outer epidermal cells walls, epicuticular waxes, trichomes and prickle hairs were depicted. Using light microscopy, mesophyll orientation, fortification of the outer periclinal epidermal cell walls, sunken stomata, C4-anatomy, enrolled leaves, salt glands and leaf succulence were investigated. The ultrastructure of the salt gland of Reaumuria alternifolia was analysed by TEM. On the basis of their leaf structures the species were subdivided into a xeromorphic and a mesomorphic leaf type group. In all species of the xeromorphic group marked curvatures of the outer epidermal cell walls in combination with a tight cover of waxes were observed, which did not occur in the mesomorphic group. In contrast, a tight layer of trichomes or bladders was, except for one species, only present in the mesomorphic group. Vertical leaf angles by flagging or parahelionasty were only observed amongst the mesomorphous species. Enrolled leaves only occurred in the xeromorphous Frankenia hirsuta. All leaves except the amplexicaulous ones of Tamarix passerinoides had an isobilateral mesophyll structure. In all xeromorphous species, except for one, the stomata were either deeply sunken or protected and combined with a pronounced fortification of the outer periclinal epidermal cell walls. In the mesomorphic leaf type group, the stomata are sunken in half of the species only and the outer periclinal epidermal cell walls are not at all or only slightly fortified. Three of the four C4-plants had a xeromorphous leaf structure. Seven species were crinohalophytes, three were leaf succulent euhalophytes and three could be termed as pseudohalophytes; they are all distributed among the mesomorphic as well as in the xeromorphic leaf type group. Projected on the transect, no continuous gradient of xeromorphy can be seen. In nine out of eleven zones species of the different leaf type groups coexist due to small heterogeneities of the sites.