Philodendron opacum Croat & Grayum

Appressed-climbing vines in understory, generally fertile 2-5 m above ground; at least the juveniles often terrestrial. Internodes 2.2-9.7 (-15?) cm long, 0.4-1.5 cm wide, medium to dark green becoming grayish, matte to glossy, cracking transversely, slightly flattened on one side, drying tan or yellowish brown, coarsely sulcate; roots typically present at distal nodes, to 2 mm thick. LEAVES: Petiole 16.6-29.5 (-35.2) cm long, P/L=0.68-0.89 (-0.94), semiglossy, sheathed (55-) 62-81%, the sheath erect or involute toward apex, adnate distally or with the free portion pro- longed to ca. 1.5 mm; unsheathed portion of petiole 3.5-10.7 cm long, D-shaped or subterete, flattened above and weakly canaliculate at least distally, the margins rounded to obtuse. Lamina 17.7-43.4 cm long, 7.8-18.8 cm wide, L/W= (1.66-) 2.00-2.55 (-3.08), IQI=(0-) 2-5 (-6), thinly coriaceous to subcoriaceous, matte or velvety to semiglossy above, matte to semiglossy below, weakly to conspicuously bicolored (dark green or gray-green above, yellow-green below), narrowly to broadly ovate, broadly or ± narrowly lanceolate, elliptic, oblong or broadly oblanceolate (usually broadest below the middle), abruptly to ± gradually acuminate apically (the acumen 0.9-2.1 cm long), cuneate, truncate or rounded (very rarely obscurely subcordate by ca. 2 mm) basally, often slightly inequilateral at the petiole apex; midrib sunken and sometimes paler above, narrowly convex and paler below (but often with a dark medial band); primary lateral veins 5-9 per side, usually with interprimaries, (0.6-) 1.4-5.3 cm apart, weakly sunken above, weakly convex be- low; minor veins obscure to slightly visible below, darker; abaxial laminar surface drying moderately to densely and evenly granular or low-granular, with reticulate veins scarcely evident even peripherally; no white stitching; resin canals occasionally visible; adaxial surface virtually featureless (very obscurely and/or patchily verruculate), minutely and uniformly alveolate to (rarely) granular. INFLORESCENCES usually solitary, occasionally paired; cataphylls commonly present, 6.0-10.0 cm long, 0.4-1.8 cm wide, linear-lanceolate to broadly lanceolate, sharply z-keeled; peduncle 3.7-5.8 (-7.7) cm long (to 9.0+ cm post-anthesis), P/S=(0.33-) 0.38-0.55(-0.65), flattened on one side with the margins rounded, weakly striate distally; spathe at anthesis 12.6-17.7 cm long (to 21.6+ cm post anthesis), 1.8-3.9 cm wide, externally matte, medium green, becoming paler distally, internally pale green, disintegrating in fruit; spathe drying densely to very densely and evenly granular externally, internally densely and evenly granular, with longitudinal secretory striations about halfway to apex; acumen of spathe (0.3-) 0.8-1.1cm long. Stipe of spadix 0.3-1.7 (-3.0) cm long; spadix (5.2-) 9.0-12.8 (-14.8) cm long, the fertile male portion 0.80-1.45 cm wide, cream-white; sterile male zone 0.6-1.6 cm long, generally the thickest part of spadix; female portion of spadix 2.3-5.7 cm long (to 6.1+ cm toward fruit), F/S=(0.23-) 0.30-0.36 (-0.40), 0.9-1.6 cm wide (to 3.0+ cm toward fruit), pale green; fertile male flowers 1.0-1.8 mm long, 0.6-1.9 mm wide, irregularly polygonal; sterile male flowers 1.4-3.1 mm long, 1.0-2.6 mm wide, anvil- shaped and ± laterally compressed, drying with texture of beeswax; female flowers 2.2-2.8 mm long, 0.6-1.0 mm wide, the stylar canals (4-) 5 (-6). INFRUCTESCENCE: Ripe fruits translucent-whitish. Seeds 0.6-0.8 (-1.0) mm long, 0.15-0.25 (-0.30) mm wide, variously described as purple, purplish violet or lavender, straight to somewhat spindled or slightly curved, finely striate with the striae minutely and obscurely cancellate, drying light to purplish brown and semiglossy.