Stem anatomy of Philodendron Schott (Araceae) and its contribution to the systematics of the genus

Previous morphological analysis has indicated that subgenus Meconostigma was the basal group of the genus and sister group of a clade formed by subgenera Philodendron and Pteromischum. However, recent molecular analysis suggests Pteromischum is the sister group of the clade Philodendron and Meconostigma. The objective of this work was to anatomically describe the stem of Philodendron, searching for possible synapomorphies for the three currently accepted subgenera, and thus give support to one of the two phylogenetic hypotheses, and to contribute new and updated information about characters relevant to the taxonomy of the group. Anatomical data were obtained from 14 species of Philodendron. The main conclusions of our study were recognition of a sclerified hypodermis and storied cork in Philodendron and verification of the absence of amphivasal bundles, the presence of which was previously suggested for the genus by French and Tomlinson. The presence of a branched root vascular plexus in Meconostigma and Philodendron gives support to the phylogenetic hypothesis in which those two subgenera form a monophyletic clade. The unistratified and sclerified hypodermis, only simple vascular bundles within the periphery of the central cylinder, and a connection through a fibrous sheath between them were considered apomorphic characters of Pteromischum.