Hemiepiphytic, usually scandent or appressed-climbing or sometimes epiphytic, sometimes occurring high into canopy, rarely terrestrial; stem appressed-climbing or scandent (flowering stems often loose, semi-erect or spreading), green, sometimes with white, waxy coating; leaf scars conspicuous, 1.5--2 cm long, 1--1.8(3) cm wide; internodes sometimes weakly flattened on one side, (1)3--9(20) cm long, 0.5--3 cm diam., usually longer than broad, medium to dark green or gray-green to brownish, weakly glossy, drying gray-green to pale yellow-brown, sometimes irregularly ridged or cracked, sometimes closely tranverse-fissured; epidermis peeling, bubbling or with loose flakes; roots several per node, 15--45 cm long, drying 1--2 mm diam.; cataphylls usually sharply 2-ribbed, sometimes weakly and bluntly 1--2-ribbed, sometimes sharply D-shaped with adaxial margins winged to 6 mm high, 14--19 cm long, sharply flattened, with obtuse medial rib, green to whitish, sometimes tinged reddish, densely dark-lineate, sometimes densely dark-speckled, deciduous intact, margins minutely undulate; petioles (7)20--38 cm long, 5--15 mm diam., subterete to obtusely flattened, rarely D-shaped, sometimes with a thin, medial rib toward apex, sometimes with adaxial margins winged to 6 mm high, spongy but brittle (fresh), medium to dark green, obtusely to sharply flattened to sulcate adaxially, the margins at least sometimes acute, broadly rounded abaxially, surface matte to semiglossy, densely short dark green lineate or speckled, with a deep maroon to purple ring around apex; sheath flattened, unopened, to 3--10 cm long, for up to half the length of the petiole; blades oblong-elliptic to narrowly ovate or narrowly oblanceolate-elliptic, subcoriaceous, weakly to moderately bicolorous, acuminate to long-acuminate at apex (the acumen inrolled or apiculate and sometimes downturned, 1--4 mm long), subcordate, obtuse to narrowly rounded or weakly cordate at base, (14)18--61 cm long, 8--19 cm wide (1.57--5.4 times longer than wide), (1.1--3.89(6.3) times longer than petiole), margins weakly undulate; upper surface dark green, semiglossy to moderately glossy, drying blackish brown to dark grayish or grayish brown, lower surface moderately paler, matte to weakly glossy, mottled violet-purple or maroon, drying dark olive-green to yellow-brown, dark olive-brown or dark brownish black; posterior lobes, when present, rounded to narrowly rounded, about as broad as long, 4--5 cm long, 5.5--6.6 cm wide, held close to petiole; sinus somewhat V-shaped, 0.5--3 cm (mostly 2.5 cm) deep; midrib flat to broadly convex, concolorous to paler than surface, sometimes sparsely purple-speckled near base above, narrowly rounded to convex to broadly convex, sometimes round-raised, paler or darker than surface, or sometimes concolorous below, sometimes sparsely purple-speckled near base below; basal veins not evident or 1--3 per side; primary lateral veins 4--8(12) per side, departing midrib at a 40--70(75)E angle, more or less straight or slightly curved to the margins, dark green, weakly sunken to etched, concolorous above, weakly raised to convex and paler than surface below (sometimes with purple spots on older leaves), drying brownish; interprimary veins obscure to impressed, paler than surface, weakly sunken above, weakly raised, darker than surface below; minor veins weakly visible above, very close, obscurely and weakly raised, darker than surface below, arising from both the midrib and primary lateral veins.

INFLORESCENCES erect, 1(2) per axil; peduncle (5)7.5--17.5(28) cm long, 7--10 mm diam., subterete, obtusely angular to 3-sided, pale to medium green; spathe 10--19.5 cm long, 1.5--2 cm diam. (to 6.5 cm wide when flattened) [(0.8--1.3)1.4--1.6(1.8) times shorter than peduncle], semiglossy, acuminate at apex, barely or not at all constricted, ribbed on back, margins revolute; spathe blade white or cream, sometimes sparsely red-spotted outside, sometimes tinged purple-violet on outer margin, 7--8.5 cm long, 1.7 cm diam. (opening 7.5--7.8 cm long, 3.2--4 cm wide), whitish inside; resin canals bright orange, appearing throughout lower 3/4 of spathe and to near base of tube inside; spathe tube oblong, pale to medium green with pale violet nearest base, sparsely red spotted outside, 6.5--7 cm long, 1.2--1.5 cm diam., glossy, whitish or pale green, sometimes red to violet-purple (B & K purple 5/10) near base or throughout tube inside; spadix more or less tapered with slight bend, held more or less erect, protruding forward from spathe, rounded at apex, (8.3)11--15.5 cm long; pistillate portion light green, (1.4)3.7--6.5 cm long, 9--13(16) mm diam. at apex, 10--14(17) mm diam. at middle, 9--12(15) mm diam. at base; staminate portion (6.8--7.2)10.5--11.2 cm long; fertile staminate portion (9)11--16 mm diam. at base, (7)11--16 mm diam. at middle, (5)9--11 mm diam. ca. 1 cm from apex, broadest slightly above the middle, as broad as or broader than the pistillate portion, as broad as or slightly narrower than the sterile portion; sterile staminate portion generally broader than pistillate portion, whitish or tinged faintly violet, 1--1.2 cm diam.; pistils 1.2--2.7(3.5) mm long, (0.8)1.1--1.9(2.6) mm diam.; ovary (5)6--8-locular, 0.8--1.8(2.4) mm long, (0.8)1.1--1.9(2.6) mm diam., walls embedded with granular, crystal-like particles; locules (0.8)1.1--1.8(2.4) mm long, (0.1--0.2)0.4-0.7 mm diam., ovule sac 0.5--0.7(1--1.3) mm long, with sub-basal placentation; ovules 1 per locule, contained within translucent, gelatinous envelope, 0.2--0.6 mm long, usually longer than funicle; funicle 0.1--0.2(0.4) mm long, style 1--6 mm long, (0.8--10)14--19(26) mm diam., similar to style type B or type D (rarely to type C); central style dome sometimes present; style apex flat to rounded or sloping; style boss sometimes present; funnel shallow when present; stigma somewhat cupulate, truncate, unlobed to subdiscoid, (0.4)0.9--12 mm diam., 0.1--0.3 mm high, covering center of or entire style apex, inserted on center of style apex or style boss or funnel if present, sessile, papillate, semiglossy; the androecium truncate, margins irregularly 4--6-sided, 1--3 mm long; thecae oblong to ovate, sometimes ellipical, 0.3--0.6 mm wide, more or less parallel to one another or contiguous; pollen subspheroidal to oblong or obovoid; sterile staminate flowers usually 4--6-sided, 1.2--2.2 mm long, 1.3--2 mm wide.

INFRUCTESCENCE with berries oblong-elliptic, 3 mm long; seeds oblong, light yellow-brown, 1.4 mm long, 0.4 mm diam., narrowly ribbed longitudinally. JUVENILE blades with lower surface sometimes tinged maroon.

Philodendron ligulatum ranges from Nicaragua (Chontales and Zelaya) along the Atlantic slope of Costa Rica and along the Atlantic slope and Continental Divide of Panama to Colombia (Antioquia and Chocó). It occurs in Tropical wet forest and Premontane rain forest life zones, from sea level to 1200 m elevation (to 600 m in Nicaragua and 650 m in Costa Rica).

Philodendron ligulatum is a member of P. sect. Calostigma subsect. Glossophyllum ser. Glossophyllum. This species is characterized by its somewhat scandent to appressed-climbing habit, generally elongate internodes, sharply 2-ribbed to obtusely 1-ribbed cataphylls, more or less spongy, obtusely flattened to somewhat D-shaped petioles clearly demarcated from the blade by a purple ring, usually more or less oblong blades narrowly cordulate at the base (or with the blades ovate and cordate) with usually 1--2 free basal veins, and usually 1--2 inflorescences per axil.

This species comprises three varieties. Philodendron ligulatum var. ligulatum ranges throughout the range of the species, whereas P. liguatum var. ovatum and P. ligulatum var. heraclioanum are endemic to Panama. See under those varieties for the differences separating them from P. ligulatum var. ligulatum. Philodendron ligulatum var. ovatum is endemic to central Panama in Coclé and Veraguas Provinces, while P. ligulatum var. heraclioanum is known from far eastern Panama in San Blas and Darién.

Philodendron ligulatum is probably close to P. correae from upland Chiriquí in western Panama. The latter species differs in lacking distinct primary lateral veins. It also differs in occurring at generally higher elevations (780--1400 m).

Philodendron ligulatum may also be confused with P. immixtum, also a vine but with smaller leaves. See under the latter species for a discussion of the differences. Philodendron ligulatum may also be confused with P. wendlandii. The latter has similar blades and spongy petioles, but differs in being a true epiphyte with short internodes and petioles sharply flattened adaxially and usually much broader than thick.

The protologue of P. ligulatum describes a sterile plant, whereas Schott's color plates (Icones) depict fertile material. None can therefore be used as type material. In addition, Engler's Araceae No. 180 prepared in 1883 and said to have been collected from the living type plant was not studied by Schott. This species is represented by excellent illustrations of fertile material by Schott, one of which could have served as a neotype, but it was deemed best to select a new fertile specimen for the neotype.

The names Philodendron ligulatum and P. lingulatum (L.) K. Koch (P. subg. Pteromischum) have been confused in the past. Pursuant to an unpublished request for a recommendation by the Committee for Spermatophyta, the two names have officially been ruled not confusable, hence not homonymous (see Nicolson, 1994: 280).

Key to the varieties of P. ligulatum

1. Petioles sharply D-shaped with undulate lateral margins adaxially; lower leaf blade surface mottled purple-violet or maroon; ovaries with 2 ovules per locule (lacking an obvious ovule sac); eastern Panama, 0--200 m.
var. heraclioanum Croat

1. Petioles subterete, at most obtusely somewhat flattened adaxially; lower leaf blade surface not colored; ovaries with 1 ovule per locule, contained within an obvious ovule sac; Nicaragua to Panama.

2. Leaf blades 1.5--1.7 times longer than wide; peduncles longer than spathe; Panama, 770--1200 m.
var. ovatum Croat

2. Leaf blades 2--4.5 times longer than wide; peduncles shorter than or about as long as spathe; usually occurring below 800 m (rarely to 1200 m).
var. ligulatum

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