Morphoanatomical and histochemical characteristics of the epiphytic fern Pleopeltis macrocarpa (Polypodiaceae)

Pleopeltis is a genus of the family Polypodiaceae, whose circumscription is still unresolved. The genus comprises about 90 species distributed mainly in the Neotropics. The apomorphies of the genus include the presence of persistent peltate scales and foliar nectaries. In Argentina, Pleopeltis macrocarpa (Bory ex. Willd.) Kaulf. is distributed in the Yungas ecoregion and in the Paranaense region. The aims of this work were to analyze the morphoanatomical characteristics and conduct histochemical studies of the glands present in foliar and rhizome scales to evaluate the secretion products. Samples were collected from different localities of Catamarca and Tucuman and deposited at the herbarium of Fundacion Miguel Lillo (LIL). Leaves were cleared; cross sections of the lamina, petiole, rhizome and root were made and treated with different stains. The study of the characters mentioned as apomorphic for the genus (scales and nectaries) involved histochemical techniques. The results show that Pleopeltis macrocarpa is a drought-tolerant species and that both the environment characteristics and the anatomical and morphological traits correspond to those of a xeric or semi-xeric plant. This work makes novel contributions regarding the description of glands in foliar and rhizome scales and paraphyses; the determination of chemical compounds of the glands; the description of the cellulosic thickenings in cells of the scale wings, the fimbriae at the base of rhizome scales and glandular hairs in the abaxial epidermis; and the confirmation of the presence of foliar nectaries and description of their structure.