Terrestrial or hemiepiphytic; internodes 1-20 cm long, 2.1-2.8 cm diam., dark green, becoming brown, glossy, somewhat flattened on one side with 2 blunt to moderately acute ribs; cataphylls 26-28 cm long, medium green, moderately soft and acutely D-shaped, the margins weakly raised, persisting semi-intact at uppermost nodes, as a few fibers lower on stem; petioles (43-)60-86 cm long (averaging 72.5 cm), 9-13 mm diam. at middle, erect to erect-spreading, acutely D-shaped near apex, bluntly so further down, medium green, weakly glossy, sparsely and inconspicuously dark-lineate; blades ovate-triangular, broadly acuminate at apex, conspicuously cordate at base, 40-56 cm long, 25-44 cm wide (averaging 47 X 34.3 cm), 1.2-1.6 times longer than broad, 0.5-0.8 times length of the petioles, broadest near point of petiole attachment; upper surface dark green with a somewhat velvety sheen, lower surface slightly to moderately paler and semiglossy; anterior lobe 31-39 cm long, moderately thin to thinly coriaceous; posterior lobes 14-22 cm long, 10-15 cm wide, directed very slightly inward; sinus spathulate, 11-16 cm deep, 4-10 cm wide; midrib broadly concave and slightly paler above, narrowly rounded and slightly paler below; basal veins 8-10 pair, first 3 free to base, others coalesced, narrowly sunken and concolorous above, round-raised and paler below; posterior rib naked for 2-3 cm; primary lateral veins 5-8 per side, departing midrib at 45°-60° angles, ascending to margin, narrowly sunken and concolorous above, round-raised and paler below; minor veins weakly raised above, moderately distinct. INFLORESCENCES 1 per axil; peduncle 6-8 cm long, 3-5 mm diam., medium green, semiglossy, sparsely short white streaked near apex; spathe tube maroon inside, dark maroon-burgundy outside, ellipsoid, 5-6 cm long, 16-21 mm diam.; spathe blade maroon inside, tinged reddish on outside, 4-7 cm long, 1.5-2.5 cm wide; spadix erect; pistillate portion tapered, 3.6-4.0 cm long, 10-14 mm diam.; staminate portion cylindroid, 3-3.9 cm long, 7-12 mm diam.; sterile staminate portion ellipsoid, 1.5-1.9 cm long, 10-11 mm diam.; staminate flowers 0.8-1.5 mm long, 1.1-1.4 mm wide; sterile staminate flowers 2.2-3.0 mm long, 1.2-1.4 mm wide; pistils 2.4-2.7 mm long, 1.4-1.8 mm wide; stigma 0.4-0.6 mm diam.; locules 5 per ovary; ovules 16-20 per locule, in 2 series, 3-5 mm long. INFRUCTESCENCES erect; peduncle to 10 cm long, 10 mm diam.; spathe tube 7 cm long, to 3.5 cm diam.
Philodendron prominulinervium is endemic to Colombia (Narino), at elevations of 1,700-1,900 m, in Premontane wetforest life zone. This species has been seen several times at La Planada, including in the regrowth forest on the trail above "La Posada and along Sendero La Rosa to Potrero de Hermogenes.