Tritomophyllum (Schott) Engl.,
Martius, Fl. Bras. 3(2): 144. 1878.
TYPE: P. tripartitum (Jacq.) Schott (designated by Mayo (1990).
The section is distinguished by having a scandent habit, three-lobed leaf blades and 1-2 ovules per locule. The section ranges from Mexico to South America, ranging as far as Ecuador on the Pacific slope and to Venezuela, the Guianas and the Amazon basin. It is represented in Central America by six species: P. angustilobum, P. anisotomum, P. cotobrusense, P. madronoense, P. rothschuhianum, and P. tripartitum. In South America there are a number of 3-lobed species, including: P. barrosoanum, P. cataniapoense, P. effusilobum, P. holtonianum, P. hylaeae, P. levelii, P. panduriforme, and P. victoriae, all now tentatively placed in P. subsect. Bulaoanum, which might belong with P. sect. Tritomophyllum. Certainly P. hylaeae with 1-2 ovules per locule and a strong similarity with P. triphyllum would appear to be closely related to P. sect. Tritomophyllum.
Bunting (1986) placed P. cataniapoense in P. sect. Oligospermium "Gruppe" Doratophyllum (now P. subsect. Bulaoanum) but having a single ovule per locule, elongate internodes and deciduous cataphylls. The species may properly belong with P. sect. Tritomophyllum.
Some of the above mentioned South American species are doubtful since they have several ovules per locule. Philodendron levelii has 2-4 sub-basal ovules and P. barrosoanum has 4-6 ovules attached in the axils above the base. Philodendron victoriae is apparently closely related to P. barrosoanum so it probably has similar ovules. It is possible that none of these species belong to P. sect. Tritomophyllum but on the other hand they do not closely match P. bulaoanum, the type species of P. subsect. Bulaoanum either.