Stem scandent, internodes 3-5 cm long, 2-2.8 cm thick. Cataphyll linear-lanceolate, 20-25 cm long, soon deciduous. LEAVES: Petiole rather terete or occasionally levelled on the upper side, 30-45 cm long, 1.5-1.8 cm thick; blade subcoriaceous subcordate-sagittate, 40-60 cm long, 25-35 cm wide; posterior lobes broadly ovate, obtuse or very obtuse, strongly unequal-sided, the outer side 2 times wider than the inner side, 10-15 cm long and sub-equally as wide; anterior lobe gradually narrowing towards the apex, eventually cuspidate; midrib thick in the lower part, disappearing towards the apex; 5-6 basal primary lateral veins on each side, united in the posterior ribs, naked for 1.5-2 cm long in the sinus; 5-6 costal veins spreading at an obtuse angle, ascending slightly arcuately near the margin. INFLORESCENCE: Peduncle 2.5-3.5 cm long, 4-6 mm thick. Spathe tube oblong, externally yellowish green, internally dorsally purplish, 4-5 cm long, 1.6-2 cm wide; blade ovate, apex shortly apiculate, 4-4.5 cm long, 3 cm wide, externally pale greenish yellow, internally sulphur-white. Spadix cylindroid with an 8 mm long stipe; female zone 3-3.5 cm long, almost 2 times shorter than the male zone. Pistils oblong-ovoid, ca. 2.5 mm long, 10-12-locular; stigma discoid, orbicular; ovules affixed somewhat below halfway up the locule. Male flowers usually 4-androus.
The species has leaves similar to P. acutatum Schott, but differs in being a much more robust plant with shorter, thicker internodes on flowering plants and by having stouter, more numerous inflorescences (up to 6 per axil). The generally large leaf blades are much longer than broad, typically somewhat triangular with conspicuously naked posterior ribs. The species is also similar in many respects to P. barrosoanum Bunting, but in that species the leaf blade is more decidedly 3-lobed.
Philodendron grandifolium ranges from northern and western Venezuela to the Guianas, ranging from sea level in the eastern part of its range to 1,260 m in the Andes. In Venezuela, the species is known from Tachira, Merida and Yaracuy in the western Andes, throughout most of the Cordillera de la Costa (Aragua and the Distrito Federal) as well as in the Delta Amacuro.