Hemiepiphyte, appressed-climbing as a juvenile plant, then spreading in the canopy with ultimate branches pendent, flowering from pendent branches [description from dried material]. Juvenile plants appressed-climbing; internodes 3-3.5 cm long, drying light reddish yellow-brown and longitudinally acute-ribbed; cataphylls pinkish, 2-3.5 cm long, tightly clasping stem, drying dark brown; petioles erect, short; blades shingled, narrowly ovate, 6-9 cm long, 3-4 cm wide, narrowly long-acuminate, dark green and matte above, drying dark brown above, moderately paler and yellow-brown below; primary lateral veins weakly sunken above in 2-3 pairs, arising at 30° angle; cross-veins distinct on the upper surface. Adult plants with internodes 3.5-6.5(-8) cm long, 0.8-1 cm in diam., glossy, dark green, smooth, light yellow-brown and acutely ribbed on drying on adult stems. Cataphylls 13-18 cm long, sharply 2-low-ribbed, heavily tinged reddish when fresh, persisting semi-intact, becoming fibrous toward the base, yellowish brown at upper nodes. Petioles subterete, 17-19 cm long (averaging 18 cm), 1-1.3 cm in diam., spreading-arching laterally, medium green, weakly glossy, conspicuously constricted at apex, blackened on drying. Blades pendent, narrowly ovate, 24-27 × 9-10 cm (averaging 25 × 9.3 cm), 2.65× longer than wide, somewhat inequilateral with one side up to 0.8 cm wider, narrowly long-acuminate at apex, subcoriaceous, pinkish when young, drying matte, dark blackish brown on both surfaces, sometimes grey, weakly paler below, margins strongly undulate; major veins drying concolourous above, darker than surface below; midrib flat and concolourous above, drying flat and concolourous below; primary lateral veins 4-6 pairs per side, weakly sunken and concolourous above, convex and darker below, departing midrib at 30-40° angle; interprimary veins moderately distinct; minor veins moderately fine and close, obscure. Inflorescence 1 per axil; peduncle 1.5-2 cm long, hidden completely by the subtending petiole sheath and cataphylls (these sometimes fibrous), drying 0.3 cm in diam. midway. Spathe 8-10.5 cm long, to 1.2 cm in diam., stiffly erect at anthesis and opening broadly, rounded at apex with a short cusp, weakly constricted midway, convolute at the base, semiglossy and densely short pale-lineate throughout, yellowish along the margin outside, medium green to light green outside on tube, pale greenish white on blade outside, greenish white throughout, inside with fine light green vertical resin canals visible, these less than 1 mm wide, spaced 2-3 mm apart, the margins of the spathe brownish on both surfaces; tube 4.5-5 cm long, 2 cm in diam. (flattening to 5.7 cm wide). Spadix 7-9 cm long, yellow-white, stipitate (stipe bright red), protruding prominently forward at about 45° angle at anthesis, scarcely or not at all constricted above the sterile staminate portion, faintly pinkish red; pistillate portion 2.7-5 cm long, 1.2-1.4 cm in diam., drying 0.9-1 cm in diam.; staminate portion 6.5-10.5 cm long, 1-1.3 cm in diam.; sterile staminate portion 1 cm long, 1.5 cm in diam.; fertile staminate portion weakly constricted above the sterile staminate portion to 1.1 cm in diam., drying 0.8-0.9 cm in diam., ending abruptly at apex in an acute tip. Pistils 3.5 mm long, 5-6-locular; stigmas 1.6 mm in diam. (dried); ovules basal, 3-4 per locule, to 1.5 mm long; the funicle about as long as the ovule. – Flowering in the rainy season, beginning in November.
Planta hemiepiphytica; internodia adulta 3.5-6.5(-8) cm longa, 8-10 mm diam.; cataphylla 13-18 cm longa, 2-costata, persistentia semi-intacta; petiolus subteres, 17-19 cm longus, 1-1.3 cm diam.; lamina anguste ovata, 24-27 cm longa, 9-10 cm lata, nervis primariis lateralibus 4-6 utroque; inflorescentia solitaria, pedunculo 1.5-2 cm longo; spatha 10.5 cm longa, tubo 4.5-5 cm longo, 2 cm diam.; spadix 9 cm longus, parte pistillata 2.7 cm longa, 1.2 cm diam., pistillis 5-6-locularibus, ovulis 3-4 per loculum.
Philodendron ushanum has been collected only in the type locality in French Guiana at 10-150 m elevation, but it has also been seen at Savanne Roche la Virgenie about 6 km east of the Mataroni River. The region where the species is known to occur is probably tropical wet forest (Holdridge 1967); though no Holdridge lifezone map exists for the area, it falls within the parameters for that lifezone. The region has 4000 mm of rain per year with a weak dry season in August till the first half of November. Daytime temperatures range from 28-33 °C while night time temperatures are 21-23 °C.