This research aimed to study the leaf anatomy of the weed species Amaranthus deflexus, Amaranthus spinosus, Alternanthera tenella and Euphorbia heterophylla, widely known in Brazil, to acquire a better understanding of the barriers each species imposes to herbicide penetration, and to other substances used for leaf spraying. Completely expanded leaves from the third to the fifth nodes were collected from spontaneous plants in the field. Three samples approximately 1cm², were removed from the medium portion of the leaves, from each species. These samples were used for structure, clarification and scanning-electron microscope observations. All species were amphistomatic. The potential major leaf barriers to herbicide penetration in A. deflexus and A. spinosus were, respectively, high cuticle thickness in the adaxial side and high cuticle thickness in both sides, respectively, whereas in A. tenella, high cuticle thickness on both sides, high content of epicuticular wax and high trichome density were the major potential barriers observed. E. heterophylla showed high content of the epicuticular wax, high latex glandular density and high cuticle thickness in the adaxial side as possible major barriers to herbicide penetration.
cuticle; epicuticular wax; stomata; trichome; vascular bunches
