Philodendron scalarinerve Croat & Grayum

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, longitudinally 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 erect-spreading, 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 subcordate at base, 33–67 cm long, 11.4–40 cm wide (1.2–4 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 semiglossy, obscurely dark-punctate at 10x 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 degree angle, arcuate-ascending to the margins, sunken above; minor veins arising from the midrib only; with scalariform "cross-veins" weakly visible when fresh, conspicuously raised above on drying, barely visible below. Inflorescences spreading, pendent, shorter than leaves, 1–4 per axil; peduncle 6–20 cm long, subterete, white-streaked near apex, spongy; spathe 16–21.5 cm long (0.6–1.4 times 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 staminate 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 placentation; locules (0.7)1.5–1.8(3) mm long, 0.4–0.6 mm diam.; ovules (10)12–14 per locule, arranged in series of 2, (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 subdiscoid, truncate 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, more or less 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, rare 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 forest , tropical lower montane forest, and tropical forest (Colombia). Philodendron scalarinerve is a member of P. sect. Philodendron subsect. Philodendron ser. Fibrosa. This species is distinguished by its short internodes, bluntly 1﷓ribbed to unribbed cataphylls which persist 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 which extend between the minor veins) numerous and conspicuous on both surfaces and uniformly greenish spathes. The collection from Ecuador (Thompson & Rawlins 761) differs from Colombian material in having the blades obtuse at the base, however this feature is common in plants from Panama. An apparently closely related species occurs in the Amazonian basin in Colombia (Schultes & Smith 3008 in Putumayo Department), Ecuador (Cerón & Neill 2526 and Hurtado & Alvarado 1073 in Napo Province), and Peru (Rimbachi 326 in Loreto Department). These specimens differ in lacking the minute dark punctations typically visible on the dried lower leaf surface of P. scalarinerve, and in lacking the conspicuous "cross﷓veins" typically visible on the dried upper blade surface. Instead, they have conspicuous "cross﷓veins" on the lower blade surface.