Stem morphoanatomy of six species of Phoradendron Nutt. (Viscaceae)

Abstract

 In this study, we analyzed the morphology and anatomy of stems of six mistletoe species (Phoradendron, Viscaceae) in Maringá, in the state of Paraná. According to the species, the stem may present several shapes in transversal section: circular, losangular with expansions in the extremities or square. The stem is covered with a thin cuticle; epidermic cells form a papilose surface, little or very prominent depending on the species; they present external anticlinal and periclinal very thick and cutinized walls. After secondary growth, this walls and cuticle can break up, forming a cicatrization tissue marea; papilose epidermis may help in the extension growth. Cortical parenchyma is photosynthetic and presents brachysclereids, idioblasts with crystals, phenolic and lipidic substances and also accumulates lipids. Vascular bundles present secondary growth even in the first internodes, originating a compact vascular system with rays containing abundant amyloplasts. The primary phloem and xylem form fibers. The pith initially parenchymatous becomes sclerified with crystals, starch and brachysclereids groups. The shape of the stem in a cross section is the most suitable feature for taxonomic purposes, whereas the anatomical characters complement this.