Philodendron tenue K. Koch & Augustin,
in A. Braun et al.. Append, gen. sp. Hort. berol. 1854: 7. 1854-1855. TYPE: Cultivated at Berlin, origin unknown (holotype, B? lost); Schott ic. 2465 and 2466 (neotype, here designated, W). Figures 404-407, 413, 414.
Philodendron gracile Schott, Prod. syst. Aroid. 244. I860. TYPE: Costa Rica. Wendland s.n., not seen (holotype, W? now lost; impression of type is at K); Schott ic. 2687-2688 (neotype, here designated).
Philodendron ecuadorense Engl., Hot. Jahrb. Syst. 26: 531. 1899. TYPE: Ecuador. Manabi, Eggers 15221 (holotype, B; isotype, F).
Philodendron sodiroanurn Engl., Bol. Jahrb. Syst. 26: 531. 1899. TYPE: Ecuador. Pichincha: Nanegal, Sodiro 47 (holotype, B).
Usually hemiepiphytic, rarely terrestrial or epilithic; stem usually appressed-climbing, thick, short, leaf scars inconspicuous; internodes striate, 2-3.5 cm long, 1-2.5 cm diam., about as long as broad, dark green to olive-green; roots drying tan to brownish red to blackish, smooth, elongate, 7÷ 28 cm long, 0.2÷0.5 cm diam., usually few per node, rarely numerous per node, dense, spreading at the nodes, epidermis peeling; cataphylls membranous, 28÷31 cm long, 8 cm broad at base, usually unribbed, sometimes bluntly or sharply 1-ribbed to sharply 2-ribbed, green, red or purplish green, pale white-striate, drying brownish to reddish brown, persisting intact, eventually fibrous.
LEAVES ± erect; petioles 29-107 cm long, 2-11 mm diam., erect, ± terete, stiff, firm, dark green, sometimes somewhat flattened with a low medial rib adaxially, surface weakly semiglossy, weakly light green striate with many small, fine ridges; geniculum thicker than petiole, 3÷4 cm long, scurfy, slightly paler than petiole; blades ovate to ovate-triangular with prominent posterior lobes, chartaceous to subcoriaceous, moderately bicolorous, narrowly acuminate, sometimes long-acuminate at apex (the acumen inrolled, 1-4 mm long), cordate at base, 31-78 cm long, 16-52 cm wide (1.2-3.1 times longer than wide), (0.6÷1.4 times longer than petiole), margins weakly undulate, upper surface gray-green to dark green, glossy, lower surface semiglossy, paler; anterior lobe 30.5÷60 cm long, 14÷ 34 cm wide (1.5÷3.8 times longer than posterior lobes), broadest at point of petiole attachment; posterior lobes 10÷29.5 cm long, 6÷16.5 cm wide, broadest at or near the middle, directed downward and outward, sometimes inward, obtuse to sub-rounded to bluntly acute; sinus triangular, acute to almost obtuse, sometimes closed, 4.5÷17 cm deep; midrib flat to sunken, concolorous to slightly paler than surface above, raised, concolorous, drying somewhat paler than surface below; basal veins 5÷ 7 per side, with 0(1) free to base, part of the remainder coalesced 2÷10.5 cm; posterior rib not naked; primary lateral veins (6)8÷14(20) per side, departing midrib at a 65-90¡ angle, ± straight or weakly arcuate to the margins, prominently to narrowly sunken above, raised to convex below; inter-primary veins as conspicuous as primary lateral veins, weakly sunken and concolorous above, weakly raised and concolorous below; minor veins moderately visible to distinct below, arising from both the midrib and primary lateral veins.
INFLORESCENCES erect, to 4 per axil; peduncle 2-11 cm long, 3÷18 mm diam., pale green, drying reddish brown, heavily white-lineate, drying longitudinally fissured; spathe erect to erect-spreading, coriaceous, acuminate at apex, 7÷14 cm long, (1.3÷ 4.4 times longer than peduncle), moderately constricted above the tube, 2.1 cm diam. at constriction, short-lineate throughout; spathe blade weakly lanceolate, greenish white, sometimes heavily tinged red outside, 4÷8 cm long, 2.1 cm diam., (opening 3.6 cm long), white to pale green inside; spathe tube ovoid, medium to dark green, usually tinged red or sometimes dark violet outside, white-striate with clear margins in front, short, pale green lineate in back outside, 3-7 cm long, 2-3.5 cm diam., white to pale green, sometimes red at base inside, sometimes sparsely white-spotted; spadix sessile; 6-12 cm long; pistillate portion yellowish green to pale green, weakly tapered upward, 2.8^4 cm long in front, 1.9÷2.2 cm long in back, 1.1÷1.6 cm diam. at middle, 1.75 cm wide at base, 0.9÷1.5 cm ca. 1 cm from apex, with 12÷14 flowers per spiral; staminate portion 5.3÷7.1 cm long; fertile staminate portion white, drying orange reddish to light reddish, 1÷1.1 cm diam. at base, 1.2÷1.5 cm diam. at middle, 7÷10 mm diam. ca. 1 cm from apex, broadest in the middle, as broad as to slightly broader than the pistillate portion, as broad as to narrower than the sterile portion, 27÷35 flowers visible per spiral; sterile staminate portion as broad as to broader than the pistillate portion, pale brown, 11÷17 mm diam.; pistils 2.7÷3.1(6.2) mm long, 1.2-1.7(3.9) mm diam.; ovary 4÷5-locular, 1.6-2(5.9) mm long, 1.2÷1.7(3.9) mm diam., with axile placentation; locules 1.6-2(4.2-5.9) mm long, 0.4÷ 0.7(1.1) mm diam.; ovules 12-14 per locule, 2-se-riate, 0.4 mm long, longer than funicle; funicle 0.2(0.5) mm long, adnate to lower part of partition, style 0.5÷0.6 mm long, 1.2÷1.7 mm diam., similar to style type B; style apex flat; stigma cupullate, ± hemispheroid, 1.1 mm diam., 0.4-0.6 mm high, covering center of or entire style apex, depressed medially with 6÷8 holes; the androecium truncate, prismatic, margins irregularly 4÷6-sided, (0.3)0.7÷ 0.9 mm long, 1.1÷1.4 mm diam. at apex; thecae oblong, 0.3-0.4 mm wide, ± parallel to one another, nearly contiguous; sterile staminate flowers irregularly 4-6-sided, mostly prismatic, sometimes clavate, blunt, 1.3÷2.5 mm long, 1.4÷2.5 mm wide.
INFRUCTESCENCE with fruits purplish.
Flowering in Philodendron tenue occurs during the dry season and early rainy season (January through August, perhaps especially April and May). Post-anthesis collections are from January to October, and immature fruits are known from April through November.
Philodendron tenue ranges from Nicaragua to southern Ecuador (El Oro) on the Pacific slope, and in Venezuela along the foothills of the Sierra de Perija (Zulia), through the Cordillera de la Costa (Yaracuy to the Distrito Federal at Cerro Naiguata) and in the foothills of the Cordillera de Merida south to Apure. In Central America it ranges from 20 to 1400 m in elevation in Premontane wet forest, rarely in Tropical moist forest. In Colombia it has been collected to 2300 m, and in Ecuador to 1930 m. Philodendron tenue is ecologically quite versatile in South America, where it occurs in Tropical thorn woodland. Premontane thorn woodland. Tropical dry forest. Tropical moist forest, and Premontane wet forest life zones.
Philodendron tenue is a member of P. sect. Philodendron subsect. Philodendron ser. Fibrosa. This species is characterized by its epiphytic habit, short internodes, persistent cataphyll fibers, more or less terete petioles (equal to or longer than the blades), and especially by its ovate to ovate-triangular blades with prominent posterior lobes often directed outward, narrow to almost closed V-shaped sinus with the posterior ribs not at all naked, and anterior lobe with numerous close primary lateral veins.
Philodendron tenue is similar and perhaps related to P. maguirei G. S. Bunting, but that species is terrestrial, has fewer primary lateral veins (typically 3÷6 vs. 8-20 for P. tenue), and petioles drying straw-yellow (vs. green to brown for P. tenue).
The species can be confused with narrow-leaved epiphytic forms of P. thalassicum in Costa Rica, but that species has a somewhat glaucous epidermis on the abaxial blade surface and also uniformly greenish spathes.
It is strange that P. tenue is found on both sides of the Andes (an unusual pattern except for the most weedy of species), but still does not extend southward from Venezuela. It should certainly be expected at least in Amazonian Colombia.