Philodendron scalarinerve Croat & Grayum, Ann. Missouri Bot. Gard. 84(3): 521–523. 1997.
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.
Type: Panama. Panamá: road past and 3--3.5 mi. NE of Altos de Pacora, 7.8--8.2 mi. above PanAmerican Hwy., 11.1--11.6 mi. beyond Lago Cerro Azul, 700--750 m, 9°15'N, 79°25'W, Croat
68692 (holotype, MO-3585744; isotypes, B, CAS, COL, CR, F, K, NY, PMA, US).
Carchi: Chical, 1200--1250 m, 0°56'N, 78°11'W, Thompson & Rawlins 761 (CM, MO); Parroquia Tobar Donoso, Reserva Indígena Awá, Centro El Baboso, 1800 m, 0°53'N, 78°25'W, Tipaz et al. 1697 (MO). Napo: Along road between Coca and the main Baeza-Tena Road, via Loreto and Hollín; 6.7 km W of Loreto, 109.7 km W of Río Payamino, 26.3 km E of main Baeza-Tena Road, 1050 m, 0°48'S, 77°32'W, Croat 72650 (MO). Pastaza: Canton Puyo, Parque Pedagogico Etnobotanico OMAAERE, 900 m, 1°27'S, 77°58'W, Cerón 31102 (QAP); Hacienda San Antonio de Barón von Humboldt, 2 km NE of Mera, 1100 m, 1°27'S, 78°6'W, Zaruma, et. al 7 (MO). Morona-Santiago: along road between Macas and Puyo, 31 km N of Macas, 28.5 km N of bridge over Río Upano, 1125 m, 2°1'S, 77°56'W, Croat 72795 (COL, HUA, MO, US). Río Amundaló, Colonia Tarqui, 970 m, 1°41'S, 78°1'W, Cerón et al. 35628, 35663 (QAP).