Micromorphological study of leaf surfaces structures in selected Crataegus L. (Rosaceae) species using light, scanning electron, and confocal laser microscopy.

A comprehensive micromorphological analysis of leaf surfaces was conducted on three model species of the genus Crataegus L. - Crataegus monogyna Jacq., Crataegus sanguinea Pall., and Crataegus submollis Sargent. - representing three subgenera: Crataegus, section Crataegus; Sanguineae, section Sanguineae Zabel ex C. K. Schneid.; and Americanae, section Coccineae Loudon (subtribe Malinae, Rosaceae). The study encompassed developmental stages from bud to mature leaf. Previously undescribed colleters were found on leaf blades and stipules of all species, which differed in petiolar colleter presence and traits. Intensive secretion occurred during intra-bud and early extra-bud stages. Secretory products accumulated in intercellular and periplasmic spaces and were released upon rupture of cell walls and cuticle; the secretion contained a red fluorochrome (715 nm). All species exhibited anomocytic/stephanocytic stomata on the abaxial leaf surface. Stomata were largest in C. monogyna and smallest in C. sanguinea. However, rare stomata were observed on the adaxial surface of leaf blades in C. monogyna, as well as on the adaxial side of marginal teeth in C. submollis and C. sanguinea. All three species showed stomatal dimorphism, radial cuticular (lateral) folds, and an annular folding (marginal stomatal ring). However, in C. monogyna, pronounced radial folds were observed only in larger primary stomata. Prominent cuticular folding was present on the adaxial epidermis of this species, accompanied by well-developed epicuticular wax on the abaxial side. By contrast, C. submollis and C. sanguinea showed weak adaxial folding and no abaxial wax deposits. These micromorphological traits may thus serve as valuable taxonomic markers within Malinae and Maleae (Rosaceae).