Glandular Trichomes of Fagonia L. (Zygophyllaceae) Species: Structure, Development and Secreted Materials

The glandular trichomes of Fagonia consist of one secretory cell and a multicellular stalk, which develops by division, elongation and elevation of epidermal cells. The latter become seperated from the mesophyll and a subepidermal chamber is formed. The length of the stalk, which differs in the various species or varieties is determined by the number of cell divisions and /or the extent of cell elongation. Although the basic morphology and development of the trichomes of the species and varieties examined are similar, two types of mature trichomes can be distinguished: one occurs in the two examined varieties of F. mollis and the second in F. glutinosa and F. arabica . The secretory cells of the second type possess a very thick wall and bear a porous cupule on their top. Histochemical tests revealed that the sticky substance secreted by the secretory cells contains mainly polysaccharides and lipophilic compounds. The secreted material exhibits autofluorescence. In F. mollis var. hispida changes in the amount and shape of the fluorescent material inside the secretory cell, during the course of development, have been observed. The contribution of the glandular trichomes in Fagonia species to survival in hot desert conditions is discussed.