1. P. ser. Macrobelia
TYPE: P. sagittifolium Liebm.
Philodendron ser. Macrobelia is the largest group of species in P. sect. Macrobelium and the one most typical of the subsection which contains P. sagittifolium, the type species for the subsection. Philodendron ser. Macrobelia is distinguished by having moderately coriaceous, cordate to sagittate blades with the basal posterior rib usually not naked or only weakly naked near its base. In addition cataphylls are usually deciduous or only briefly persistent. Most of the species in the series have a strong resemblance to the widespread P. sagittifolium. All members have type D style (see section on style type), relatively few ovules per locule, usually 1-5, rarely to 6, 7, or 8 per locule. In most cases the ovules are contained within a translucent or transparent ovule sac.
Central American representative include: P. advena, P. annulatum, P. aromaticum, P. coloradense, P. dwyeri, P. edenudatum, P. ferrugineum, P. grayumii, P. knappiae, P. mexicanum, P. platypetiolatum, P. sagittifolium, P. subincisum, P. sousae, P. verapazense, and P. zhuanum.
Philodendron platypetiolatum is unusual in having a much-flattened petiole. Perhaps it warrants separate recognition. Philodendron mexicanum, long considered a member of the group is unusual in not greatly resembling P. sagittifolium and in having blades that are sometimes more or less hastate.
It is possible that P. annulatum belongs in P. subsect. Belocardium because it sometimes has a purple annular ring at the apex of the petiole and usually has only 1-2 ovules per locule (though sometimes 4-5 ovules per locule).
5. Species incertae sedis (species with unknown features or affinities)
One species in P. subsect. Calostigma, P. cotonense, remains unclassified. It has 4-5 ovules per locule and has a strong resemblance to P. wilburii in P. ser. Ovata. Perhaps it belongs to that same group although P. subsect. Belocardium has only 1-2 ovules per locule.