Hemiepiphytic scandent creeper up to 15 m high, rarely terrestrial; internodes (2-)7-20 cm long, 1-3 cm in diam., greyish green and semiglossy, turning light brown to light yellowish with brown transverse fissures, epidermis commonly flaking when dry; aerial roots with epidermis tan to reddish brown, arising just below the nodes, 1-4 at the apical nodes, up to 8 at lower nodes, up to 3 mm in diam. and up to 8 m long. Cataphylls sharply 2-ribbed (the ribs slender, 3-5 mm high), 11-13(-15) cm long, succulent, whitish to greenish, sometimes tinged red-purple with scattered purple spots, most of them at the middle, deciduous intact. Leaves erect-spreading, distributed along the stem; petioles (20-)25-35(-51) cm long, 0.5-0.8 cm in diam., terete to U-shaped (thicker than broad) in cross section, obtusely and weakly flattened adaxially, light green, faintly streaked with darker lines, sometimes with a purplish apical ring at apex; blades ovate-cordate to narrowly sagittate to oblong-cordate; gradually long-acuminate at apex, cordate at base, 20-47 × 11-26 cm, 1.7-3.7 times longer than broad, semiglossy, dark green above, moderately paler below, drying dark brown to reddish brown above, paler and sometimes greenish brown below; posterior lobes 4.5-12.5 cm long, 4-9 cm wide; sinus 4-8 cm deep, subhippocrepiform to parabolic, sometimes triangular; midrib flat and moderately paler, with short intermittent lines; basal veins (3-)4-5, 3-5 close together at base but never forming a posterior rib; the 1st pair free to the base; primary lateral veins 7-10 per side arising at 65-75° angle, sunken above; interprimary veins usually present; minor veins moderately obscure. Inflorescences 1-2 per axil; peduncle 2.5-5(-6.5) cm long, 0.5-1.2 cm in diam., pale green; spathe 8-16 cm long; green to yellowish green at the blade, reddish at the tube outside, greenish at the apex and bright reddish purple at the tube inside, weakly constricted at the middle; spadix slightly protruding at anthesis 7.9-12.8 cm long, pistillate portion 4.5-5.8 cm long, 0.5-0.7 cm in diam. at base, 0.8-1 cm in diam. midway and at apex; staminate portion 3.4-7.3 cm long, 1-1.2 cm in diam. on sterile portion at base, 0.8-1 cm in diam. at constricted portion, 1.2-1.4 cm in diam. in upper 2/3, narrowly rounded at apex; the staminate and pistillate portions often of the same length; sterile staminate portion 0.6-0.8 mm long; pistils 1.7-1.8 mm long; ovary broadly elliptic; stigma 1-1.2 mm in diam. at apex, weakly concave with the margins somewhat raised and with a weak central dome; ovary 6-8-locular, c. 1 mm long; ovules 1-2 per locule, 0.2 mm long, funicle 0.1 mm long; berries not seen.
Planta hemiepiphytica; internodia adulta (2-)7-20 cm longa, 1-3 cm diam., caulis cum fissuris tenuibus transversalis; cataphylla 2-costata, 11-13(-15) cm longa, decidua; petioli (20-)25-35(-51) cm longi, 0.5-0.8 cm diam., teretes vel U-formati; laminae ovato-cordatae vel anguste sagittatae vel oblongo-cordatae, 20-47 × 11-26 cm; venas basales (3-)4-5 utroque; nervis primariis lateralibus 7-10 utroque; inflorescentiae 1-2 in quoque axilla; pedunculus 2.5-5(-6.5) cm longus; spatha 8-16 cm longa, viridis, flavovirescens vel rubra, tubus rubellus extus, rubri-purpureus intus; spadix 7.9-12.8 cm longus; parte pistillata 4.5-5.8 cm longa.
Philodendron longirrhizum is known from the Western, Central and Eastern Cordillera of Colombia and from the Cordillera de Mérida in Venezuela, occurring at 1650 to 2500 m elevation in montane tropical forests (Holdridge 1967). Philodendron longirrhizum has been collected in flower in October to March and in fruit in May.