Anatomy of the adventitious roots of Philodendron (Araceae) and its importance for the systematics of the genus

Abstract. The genus Philodendron Schott comprises the following three currently accepted subgenenera: P. subg. Philodendron, P. subg. Pteromischum and P. subg. Meconostigma; however, these lack a well-defined classification. In the present study, we examined anatomically samples of adventitious roots in species of the group, so as to establish aspects relevant for taxonomic purposes. The anatomical analyses emphasised the characteristics of the steles in cross-sections of the root samples from regions near the apex to the most mature zones. A species of a closely related genus Adelonema, namely A. crinipes, was included in the study to clarify the results. Our results indicated notable differences in the species of the subgenus Meconostigma, mainly in terms of the presence (and variations) of a lobed stele, whereas the cylindrical stele stood out among the common characteristics in P. subg. Philodendron, P. subg. Pteromischum and the related species A. crinipes. Moreover, the characteristics shared by P. subg. Philodendron and P. subg. Pteromischum corroborated the phylogenetic hypothesis that these two taxa were more closely related to one another than to P. subg. Meconostigma.