Appressed-climbing hemiepiphyte; stems moderately short; leaf scars conspicuous, 2-4 cm wide; internodes 1÷1.5(3) cm long, 1.5÷3.5(4) cm diam., about as long as broad; roots moderately few per node, short, drying dark brown, matte, longitudi-nally ridged; cataphylls moderately thick, to 22 cm long, unribbed to bluntly 1-ribbed, rarely sharply 2-ribbed, drying dark brown, persisting semi-intact, eventually fibrous at upper nodes.

LEAVES erectspreading, clustered at or near stem apex; petioles 20÷75 cm long, 0.7÷1.5 cm diam., subterete, stiff, green, obtusely flattened, sulcate adaxially; sheathing 1÷2.5 cm long; geniculum scarcely thicker than petiole, 6÷7.8 cm long slightly paler than petiole; blades oblong-elliptic to narrowly ovate, moderately coriaceous, acuminate at apex (the acumen sometimes inrolled, to 2 mm long), obtuse to sub-cordate at base, 33÷67 cm long, 11.4-40 cm wide (1.2^1 times longer than wide), (0.82-2.11 times longer than petiole), broadest at the middle, margins weakly undulate, upper surface dark green, semiglossy, lower surface much paler, matte to se-miglossy, obscurely dark-punctate at 10 X magnification; midrib convex to narrowly raised, sometimes paler than surface above, convex to thicker than broad and concolorous below; basal veins 1÷ 4 per side, with all free to base; primary lateral veins 5÷18 per side, departing midrib at a 60-75¡ angle, arcuate-ascending to the margins, sunken above; minor veins arising from the midrib only; with scalariiorrn "cross-veins" weakly visible when fresh, conspicuously raised above on drying, barely visible below.

INFLORESCENCES spreading, pendent, shorter than leaves, l^l per axil; peduncle 6÷20 cm long, subterete, white-streaked near apex, spongy; spathe 16-21.5 cm long (0.6-1.4 limes longer than peduncle), pale green, acuminate at apex, obtuse at base, convolute to about the middle at anthesis; spathe blade semiglossy, white-streaked at apex outside, light green inside; spathe tube matte, white-streaked at base outside, 5÷7 cm long, 2÷3.5 cm diam., greenish white inside; spadix sessile, erect, (7.6)9÷12 cm long, broadest at the base or at the middle or below the middle; pistillate portion light green, slightly tapered above middle or toward both ends, (1.7)2.6-4.3(7.8) cm long, 0.8-1.3 cm diam. at apex, 0.8÷1.4 cm diam. at middle, 0.9÷1.4 cm wide at base; staminate portion 4.8÷8.7 cm long; fertile staminate portion (9)12 mm diam. at base, (9)12 mm diam. at middle, (6)10 mm diam. ca. 1 cm from apex, broadest at the base, slightly narrower than the pistillate portion, slightly narrower than the sterile portion; sterile staminale portion as broad as the pistillate portion, 1.2÷1.4 cm diam.; pistils (1.4)2.3-2.8(3.2) mm long, (1)1.4-1.9 mm diam.; ovary 4-6(7-8)-locular, (0.7)1.5-1.8(3) mm long, (1.1)1.5÷1.9 mm diam., with axile placenta-tion; locales (0.7)1.5-1.8(3) mm long, 0.4-0.6 mm diam.; ovules (10)12-14 per locule, 2-seriale, (0.1)0.3-0.4 mm long, longer than funicle; funicle 0.1÷0.2(0.3) mm long, adnate to lower part of partition, style 0.5(0.7) mm long, 1.1-1.4(2.2) mm diam., similar to style type B; style apex usually flat, sometimes rounded or domed, with stigma lobes over depressions (if apex is flat or domed); stigma usually lobed, sometimes subdiseoid or truncate, lobed, 0.9-1.2(1.4-1.7) mm diam., (0.1)0.2÷0.3 mm high, covering entire style apex, inserted on center of style apex, sometimes medially depressed; the androecium truncate, prismatic, sometimes weakly oblong to oblong, margins 4÷6-sided, sometimes scalloped, (0.6)0.8÷1.1 mm long, 1÷1.8 mm diam. at apex; thecae oblong, 0.3÷0.5 mm wide, ± parallel to one another, contiguous or nearly contiguous; pollen ellipsoidal, <0.1 mm long, <0.1 mm diam.; sterile staminate flowers irregularly 4÷6-sided, clavate or weakly rounded, blunt, rarely irregularly 3÷5-sided or depressed with a furrow, (0.8-1.2)1.7 mm long, 0.9-1.5(1.5-2 mm) wide.

Flowering in Philodendron scalarinerve occurs principally in the early rainy season (June through August) but also in March. Post-anthesis inflorescences have been collected primarily from June through September, but one such Costa Rican collection was made in January and one South American collection in December. Immature fruiting collections are known from July through December.

Philodendron scalarinerve ranges from Costa Rica to Ecuador, from sea level to 1325 m in Tropical wet forest. Premontane rain forest. Tropical Lower Montane rainforest, and Tropical rainforest (Colombia).

Philodendron scalarinerve is a member of P. sect. Philodendron subsect. Philodendron ser. Fibrosa. This species is distinguished by its short internodes, bluntly 1-ribbcd to unribbed cataphylls persisting as pale fibers with small fragments of thin, pale epidermis, terete to subterete petioles, narrowly ovate to oblong-ovate blades drying dark with the "cross-veins" (tertiary veins that extend between the minor veins) numerous and conspicuous on both surfaces and uniformly greenish spathes.