Appressed-climbing hemiepiphytic vine; internodes elongated, more than 5 cm long, 1-1.5 cm diam., drying medium yellowbrown, irregularly and sharply ridged on drying, semiglossy; cataphylls 5.2-6 cm long, green, sharply flattened on one side, deciduous. LEAVES: Petioles 25.5-31.5 cm long, less than 1 cm diam., equal to or somewhat longer than the blades, terete, drying dark yellow-brown, finely and acutely ribbed, the genicular area drying blackened, 2.5-3 cm long, sheathed 1.0-1.5 cm at the base; blades panduriforme, 26-30 × 14.5-19.5 cm, 1.5-1.8 times longer than wide, subcordate with somewhat spreading lobes at base, abruptly acuminate at apex, prominently constricted 8- 12 cm above the base; drying matte and grayish yellow above, somewhat paler and yellow-brown below; anterior lobe 24-25 cm long, the constricted area 6.5-9.5 cm wide, 9.5-14.7 cm wide in the broadest area of the anterior lobe above the constriction; posterior lobes 7.7-10.5 cm long, directed more or less outward, about as long as broad; sinus 2- 4.5 cm deep, arcuate to parabolic at apex; midrib drying +/- flattened, closely and finely ridged, darker than surface above, narrowly raised, closely and finely acute-ribbed, +/- concolorous below; primary lateral veins 3- 5 per side, arising at 65-70° angle; basal veins 3 per side, the 1st pair free to the base, spreading at 80-90° angle; major veins moderately obscure above, weakly raised and slightly paler below; minor veins moderately distinct, weakly raised below. INFLORESCENCE solitary; peduncle 6 cm long, drying blackened and finely ridged, 4 mm wide; spathe 9.5 cm long, green; spadix 9.5 cm long; pistillate spadix 2.9 cm long in front, 2.7 cm long in back, 8 mm diam. at base, 8.5 mm diam. midway, 7 mm diam. at apex; staminate portion white, 6.5 cm long; sterile portion 1 × 0.9 cm; fertile portion 1.1 cm wide in broadest portion toward the apex, bluntly tapered at the apex; pistil with stigma 0.7- 1.0 mm wide; ovary 1.8 mm long, 3-4-locular; ovules basal, 0.026 mm long; funicle 0.014 mm, the ovary borne within a translucent gelatinous envelope 0.08 mm long.
The species is characterized by long internodes, hemi-epiphytic habit, yellow-brown finely ridged dried stem, petioles about as long as the blades, and especially by the panduriform blades. Philodendron barbourii might be confused with P. panduriforme Schott, but that species has blades that are much broader and dry black. Philodendron barbourii is similar to P. nullinervium E. G. Gonç. from Brazil (Acre) and the western Amazon in having a hemiepihytic habit, long internodes, and panduriform blades. However, P. nullinervium has petioles usually longer than the blades (instead of the petioles being closer to the same length as the blades in P. barbourii). Also, P. barbourii has much shorter peduncles than P. nullinervium, and the spathe in P. barbourii is green, while the spathe in P. nullinervium is green to whitish pink outside and purple inside.