P. subsect. Macrolonchium (Schott) Engl.,
Martius Fl. Bras. 3(2): 139. 1878.

P. grex Macrolonchium Schott, Prodr. Syst. Aroid. 269. 1860.
LectoTYPE: P. simsii (Hook.) Don (designated by Mayo, 1990, p. 64). This is a small group of species characterized by D-shaped or broadly and sharply sulcate petioles and the presence of short stems with short internodes. Leaf blades typically are ovate-triangular. Cataphylls typically persist as fibers. Ovaries are 5-10 locular with numerous ovules per locule. This group was treated by Engler (1899) and by Krause (1913) as a section based on stems with internodes shorter than broad versus scandent stems but the group is in no way warranted at the sectional level based on this or any other character.

Though neither short stems nor D-shaped petioles are unique to this group, it appears to be a natural one at the subsectional level with the exception of only two pinnately lobed species in the group, P. pinnatifidum (Jacq.) Schott and P. robustum Schott. Those species are very similar to P. fendleri K. Krause, which Engler placed in his P. sect. Polytomium. Philodendron pinnatifidum and P. robustum should probably be placed there as well. They seem to have little in common with the other simple leaved species. Philodendron melinonii Brongn., P. fragrantissimum, P. simsii Kunth, and P. roraimae K. Krause all appear to be related. The only Central American species in this subsection is P. fragrantissimum.