Hemiepiphytic; appressed-climbing; internodes smooth, sparsely cracked but only weakly or not at all ribbed, somewhat flattened on one side (at least at the upper nodes), to 10 cm long, 3 cm diam., medium green, soon turning gray, drying light brown; cataphylls to 20 cm long, unribbed, green, deciduous; LEAVES: petioles 35-37 cm long, 1.5 cm diam., subterete, firm, drying reddish brown, obtusely flattened adaxially, surface drying finely and irregularly striate; sheathing at base, 4-5 cm long; blades ovate-cordate, subcoriaceous, semiglossy, weakly bicolorous, acuminate at apex, prominently cordate at base, 26-33 cm long, 17.5-25 cm wide, 1.3-1.6 times longer than broad, upper surface drying dark brown, lower surface drying dark yellow-brown; anterior lobe 20-23.5 cm long, margins convex; posterior lobes 9-12 cm long, directed somewhat upward at an angle to the midrib, drying directed toward the base; sinus obovate, 6.5--9 cm deep; midrib flat, pale green above, convex, paler than surface below; basal veins 4-6 per side, and with the first free to base, third and fourth veins coalesced 1.5-3.5 cm, pale green; posterior rib not at all naked or naked up to 2 cm, only weakly curved; primary lateral veins 4-5 per side, departing midrib at a 45-55º angle, weakly curved to the margins, pale green, weakly sunken above, weakly raised below, drying paler than surface, flattened, with acute margins below; interprimary veins only occasionally present; minor veins easily visible on both surfaces, arising from both the midrib and primary lateral veins, drying weak and paler than surface and usually alternating with blackened secretory ducts, surface minutely granular upon magnification. INFLORESCENCES 2-3 per axil; peduncle to 8 cm long, drying dark reddish brown, minutely striate, bent at ca. 140º angle beneath the spathe; spathe to 10 cm long, to 5 cm wide when flattened, drying dark reddish brown throughout within, spathe blade pale green outside, drying reddish brown with prominent resin canals extending from the blade well into the tube within; spathe tube green, finely striate outside; spadix bluntly pointed at apex, 9 cm long; pistillate portion 2.5-2.7 cm long in front, 1-1.1 cm long in back, 10 mm diam. at apex, 9 mm diam. at middle; staminate portion 8.2 cm long; fertile staminate portion 1 cm diam. at base, 1.2 cm diam. at middle, 9 mm diam. ca. 1 cm from apex, sterile staminate portion 9 mm diam.; pistils 2.5 mm long, 1.4 mm diam.; ovary 4-5-locular, with axile placentation; ovules 4-7 per locule, 2-seriate, 0.2 mm long, contained within transparent matrix; funicle 0.1--0.2 mm long, adnate to lower part of partition, style similar to style type B; style apex flat; stigma discoid, covering most of style apex except for center, drying irregularly 5-lobed, 0.9-1.3 mm diam.; the androecium truncate, weakly oblong, probably prismatic, margins irregularly 4-5-sided, mostly 4-sided, 1.3-1.6 mm diam. at apex; sterile staminate flowers irregularly 4-6-sided, prismatic, 1.4 mm wide. INFRUCTESCENCE with seeds 5-7 per locule, 0.4-0.5 mm long.
It is characterized by having grayish internodes being longer than broad, green, unribbed, deciduous cataphylls, obtusely flattened petioles, ovate-cordate reddish brown-drying blades with a spathulate sinus and a weakly developed posterior rib which is barely or not at all naked, and paired, green inflorescences bent somewhat at the apex of the peduncule. The species is perhaps closest to P. grayumii, which differs in having 7--8 (versus 4--5) locules per ovary and 3--4 (versus 5--7) ovules per locule. In addition, the lower leaf surface of P. grayumii dries glossy and is epunctate with dense secretory ducts at higher magnifications. In contrast, the blades of P. coloradense dry more or less matte on the lower surface and is minutely speckled with only sparse secretory ducts at higher magnification.