Epiphytic often appressed-climbing, sometimes terrestrial; stems to more than 1 m long; internodes short, or 6-20 cm long, 1.5-5.0 cm diam., densely, minutely and irregularly transverse-ridged, yellow-brown, scurfy and brown to reddish or reddish brown, drying light brown, 6-20 cm long when juvenile; eataphylls to 32 cm long, 6.3 cm diam. at base, reddish, densely yellowish green, densely scaly, unribbed often reddish, marcescent, persisting for a time as loose fibers at upper nodes finally deciduous; petioles 35-76(-98) cm long (averaging 49 cm), 7-17 mm diam. at middle, to 1.6 times longer than blades when young, about equaling blades on adults, purplish, terete to subterete, obtusely flattened toward apex, minutely warty, densely and minutely transverse-fissured finely wrinkled transversely, with low, irregular, thin erect ridges, densely to sparsely setose-scaly throughout (the scales greenish, mostly 4-8 mm long, flattened, branched with laciniate to erose margins); blades broadly ovate to almost rounded, acuminate at apex, cordate at base, 29-72 cm long, 27-57 cm wide (averaging 50.5 x 43.7 cm), equally as broad as long to 1.3 times longer than broad, 0.9-1.3 times length of the petioles, broadest above point of petiole attachment, subcoriaceous to thinly coriaceous; upper surface solid dark green, and semiglossy to matte-subvelvety to velvety above; lower surface moderately to much paler and semiglossy, not marked with purple, drying greenish to olive-gray above, yellowish brown to yellowish green below; anterior lobe 20-51 cm long; posterior lobes 12-28 cm long, 10-23 cm wide, directed inward; sinus usually closed, 10-23 cm deep, 0.5-1 cm wide; basal veins 9-11 pair, mostly part free to the base; midrib flat and slightly paler at base above, deeply sunken toward apex, slightly paler above, convex to narrowly rounded and paler paler, matte below; primary lateral veins 6-8 pairs, departing midrib at 40°-45° angle, ascending to margin, weakly and deeply and narrowly sunken and slightly paler to concolorous above, convex to round-raised and paler or darker, matte below; interprimary veins indistinct; minor veins weakly raised, distinct, drying wrinkled toward the margins; both the primary and interprimary veins densely granular-pubemlent on lower surface; cross-veins distinct on drying, especially below. INFLORESCENCES (1-)2(-3) per axil; peduncles purple or reddish violet, becoming brick red, 9-14 (-25) cm long, 4-10 mm diam. brownish, the surface of the peduncles and lower part of the spathe tube covered with minute, more or less reniform and erose scales over surface, these interspersed with longer hairlike green scales, especially toward the apex; spathe dark green tinged reddish outside, densely scaly or setose, 12-19 cm long; spathe tube heavily tinged purplish on outside, deep maroon to dark violet-purple throughout inside, 4-6 cm long, 15-22 (-3.2) mm diam. (to 4 cm diam. post-anthesis); spathe blade lanceolate, cherry red on lower 2/3 to white at tip on inside; spadix 10-13 cm long; the pistillate portion with flowers pale green to creamy, cylindroid, 4-5 cm long, 11-14 mm diam.; staminate portion tapered, 6-7 cm long, 9-13 mm diam. just above base, tapered to 3-5 mm diam. at apex, broadest near base; sterile staminate portion constricted in the middle, to 2 cm long, 8-9 mm diam. at base, 4-6 mm diam. at middle, 6-8 mm diam. at apex; pistils 1.6 mm long, 1.0-1.1 mm diam.; stigmas 0.9-1.0 mm wide, 0.2 mm thick, about as broad as the ovary, densely papillate-bristly, ovules 9-10 per locule, affixed to the axis of the locule near the base, 0.1 mm long, about as long as the funicle. INFRUCTESCENCES considerably swollen at base, with spathe closed; fruiting spadix to 16 cm long; pistillate portion 8 cm long, 3 cm diam.
Philodendron fibrosum ranges from southern Colombia (Cauca, Narino) to central Ecuador (Carchi, Cotopaxi, Imbabura, Pichincha), at elevations of 900-2,200 m, primarily at 1,200-1,800 m, in Lower montane moist forest, Lower montane rain forest and Premontane wet forest life zones. At La Planada the species is moderately common in all areas of the Reserve.