Domatia and leaf blade structure of Rudgea eugenioides (Rubiaceae)

Abstract

Rudgea eugenioides is a rare woody species that grows in the understory of well-preserved Atlantic Forest of Serra dos Órgãos, in the state of Rio de Janeiro, Brazil. Leaves were collected in Reserva Ecológica de Macaé de Cima, Rio de Janeiro. The anatomical characteristics of the leaf blade were examined, especially the epidermis, using light and electron microscopy. The abaxial surface was smooth, with gap domatia between the midrib and the secondary veins and papillae. Micromorphological analyses showed epicuticular wax without any ornamentation. Leaf cross sections of R. eugenioides showed that the epidermis consisted of one-layer of cells covered with a fine cuticle and parallelocytic stomata. Light microscopy revealed that the periclinal cell walls were flat and that the anticlinal walls were predominantly straight and thicker. The leaf blade contained dorsiventral mesophyll with crystal idioblasts and collateral vascular bundles. Transmission electron microscopy allowed the arrangement of the outer periclinal cell wall to be observed. The results identified anatomical and ultrastructural characteristics that may contribute to understanding the taxonomy of this species and the survival strategies it uses in this forest environment.