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1. Blades with posterior rib (union of basal veins) naked along the edge of the sinus. 2. Petioles with conspicuous, elongate, hair-like scales. 3. Petiolar scales thinly arranged and mostly in the distal 1/2 of petiole; plants terrestrial; Panama and Colombia, 830-860 m in Panama, 80-150 m in Colombia.
P. malesevichiae Croat
3. Petiole scales densely arranged, covering the entire petiole. 4. Blades ovate-triangular, typically more than 1.3 times longer than broad, semiglossy above, paler and solid light green to silvery-green beneath, Costa Rica to Colombia, 270-850 m.
P. squamicaule Croat & Grayum
4. Blades ovate, typically less than 1.3 times longer than broad, matte and subvelvety above, paler and tinged with purplish violet between the major veins below; Costa Rica to Peru (200)500-1,500 m.
P. verrucosum Mathieu ex Schott
2. Petioles smooth or least lacking scales.  
5. Petioles conspicuously and sharply flattened adaxially with lateral margins sharply raised or with a slender wing.
6. Petioles merely sharply edged, lacking an actual wing at the margin; spathe green throughout or red on tube, white on blade.
7. Blades whitish and matte below; cataphylls persisting in semi-intact fragments of thin epidermis; spathe tube green outside, at most tinged pink within; Costa Rica to Panama (Chiriquí), (775)1,000-2,100 m.

P. thalassicum Croat & Grayum
7. Blades green and semiglossy below; cataphylls persisting in a dense reddish brown, semi-intact mass; spathe tube green or bright red outside, dark red to maroon within, blade white; Belize to South America, 0-900 m. 8. Blades ovate-triangular, 1.8-2.7 times longer than wide; cross-veins conspicuous between minor veins on dried blades; spathe tube green on outside; W. Panama (Bocas del Toro to Coclé), 590-1,300 m.
P. copense Croat

8. Blades mostly ovate, 1.1-1.7 times longer than wide; cross-veins between minor veins not at all apparent; spathe tube bright red outside; Belize to South America, 0-1,000 m.
P. fragrantissimum (Hook.) Kunth

6. Petioles with a narrow marginal wing; spathe tube green to purplish outside, spathe blade pale green.

9. Blades promptly splitting into slender segments laterally, drying blackened; Costa Rica to Panama, Atlantic slope, 0-1,400 m.

P. findens Croat & Grayum
9. Blades remaining intact, drying yellow-green; Nicaragua to central Panama, mostly less than 700 m.
P. pterotum K. Koch
5. Petioles terete to obtusely flattened or U-shaped but not sharply flattened adaxially, if sulcate adaxially the margins merely obtuse.  
10. Blades whitish and matte on lower surface even on fresh leaves; petioles usually drying light yellowish brown (except sometimes not in P. strictum).
11. Blades narrowly ovate, usually more than 1.8 times longer than wide; plants commonly hemiepiphytes; Panama to Ecuador, usually <1,400 m.

P. hebetatum Croat
11. Blades ovate to broadly ovate, averaging 1.3 times longer than wide; typically terrestrial; Costa Rica to western Panama, Colombia and Venezuela, mostly at 850-1,665 m in Central America.
P. strictum G.S. Bunting
10. Blades green to yellow-green beneath, usually semiglossy to glossy; petioles drying various colors, not light yellowish brown (except P. copense, P. schottianum, and P. thalassicum).
12. Blades usually much longer than wide, usually 1.8 times or more longer than wide.  
13. Spathe tube greenish to yellow-green or whitish inside.
14. Leaf blades with lower surface matte, frequently bluish green; style apex prolonged into a short but distinct neck (style type D); central Costa Rica to western Panama, (775)1,000-2,100 m.

P. thalassicum Croat & Grayum
  14. Leaf blades with lower surface glossy to semiglossy, not at all bluish green; style apex flat, not prolonged into a distinct neck (style type B; rarely type C).  
15. Blades drying yellow-green; basal veins fewer than 5; sap milky white, drying chalky; inflorescence solitary; cataphylls to 40 cm long; Panama (Darién), 800-1,480 m.

P. albisuccus Croat
  15. Blades drying dark gray-brown to olive-green, typically somewhat blackened; basal veins usually more than 5; sap usually clear, drying dark brown to reddish; inflorescences 2-6 per axil; cataphylls less than 20 cm long.  
16. Petioles terete to obtusely flattened, lacking prominently raised lateral margins; peduncles frequently longer than the spathe; central and eastern Panama, 0-750 m.

P. panamense K. Krause
  16. Petioles usually D-shaped or U-shaped, usually flattened adaxially with prominently raised margins and a medial rib, often thicker than broad, rarely C-shaped to subterete; peduncles usually much shorter than the spathe; southern Mexico to Panama and Venezuela (Mérida), 0-1,500 m.
P. jodavisianum G.S.Bunting
13. Spathe tube red to maroon or violet-purple on inside. 17. Blades drying greenish to yellow-green (sometimes yellow brownish in P. alticola), lacking conspicuous cross-veins.  
18. Pistils with one ovule per locule; leaf blades with secretory ducts moderately obscure, the surface densely and minutely granular on drying; staminate spadix constricted above the sterile portion, the fertile portion clavate, the sterile staminate portion only slightly thicker than the pistillate portion; dried style base donut-shaped with style tubes at the bottom of a deep concavity; Panama (Chiriquí to Coclé, (750) 950-2,200 m and Costa Rica.

P. straminicaule Croat
  18. Pistils with 12-18 ovules per locule; leaf blades with secretory ducts conspicuous, the surface smooth on drying; staminate spadix scarcely constricted above the sterile portion, the fertile portion stubby and evenly tapered to the apex, the sterile staminate portion much larger than the pistillate (aproximately 1/3 thicker); dried style base raised but flattened with a narrow pale ring around its outer margin, the stigma tubes exserted like minute funnels and extending above the surface; eastern Costa Rica and western Panama, 800-2,500 m.
P. alticola Croat & Grayum
17. Blades drying reddish brown with conspicuous cross-veins. 19. Petioles drying with a conspicuous light reddish brown or yellow-brown epidermis, this smooth and often flaking; cataphylls less than 25 cm long; primary lateral veins 11-16 per side; basal veins frequently more than 8 per side; Panama (Bocas del Toro and Coclé Provinces), 590-930 m.
P. copense Croat
  19. Petioles drying dark brown, the epidermis not peeling; cataphylls more than 55 cm long; primary lateral veins fewer than 8 per side; basal veins up to 8 per side; Panama (Chiriquí, Bocas del Toro, Coclé, and Veraguas Provinces), 500-1,630 m.
P. chiriquense Croat

12. Blades only slightly longer than wide, usually about 1.5 times longer than wide or less, sometimes wider than long.

20. Leaf blades with lower surface matte, frequently bluish green, the dried waxy surface forming an areolate pattern; central Costa Rica to western Panama, (775)1,000-2,100 m.
P. thalassicum Croat & Grayum
20. Leaf blades with lower surface semiglossy (matte on P. gigas but that species has upper surface velvety), not bluish green.   21. Leaf blades matte and velvety above; central Panama in the region of the isthmus, 300-375 m.
P. gigas Croat
21. Leaf blades glossy to semiglossy above.  
22. Peduncles usually less than 10 cm long;
23. Spathe weakly constricted or not at all constricted above the tube.

23A. Spathe solid bright red on tube outside; central Panama (Veraguas & Coclé), 800-1,200 m.
P. antonioanum Croat

23A. Spathe green on tube outside (sometimes tinged weakly red on P. schottianum)
24. Cataphylls persisting usually with large fragments of glossy, yellowish epidermis; petioles drying yellowish to yellowish brown and glossy as if with a layer of shellac; Costa Rica to Panama, 600-2,200 m.
P. schottianum Wendl. ex Schott
24. Cataphylls peristing semi-intact and brown, not glossy or yellowish; petioles usually drying brown to blackened, usually not yellowish and glossy; Guatemala, 1,360-1,870 m.
P. purulhaense Croat
23. Spathe moderately to prominently constricted above the tube. 25. Leaf blades dryi Croatng yellow-brown below, coriaceous; ovules mostly (6)12-(2) per locule; Isthmus of Panama, mostly below 500 m
P. llanoense.
  25. Leaf blades drying reddish brown, moderately thin; ovules 1-6 per locule (except P. dodsonii with 20 ovules/locule); Costa Rica or Mexico.
26. Stems usually growing over rocks in dry habitats, rarely on trees; cataphylls eventually deciduous intact on the older stem; ovules 4-6 per locule; western Mexico (Jalisco & Guerrero) 350-1,250 m.
P. basii Matuda
  26. Stems appressed-climbing on trees in humid habitats; cataphylls decomposing and breaking up before falling off; ovules either solitary or up to 20 per locule; Costa Rica and/or Ecuador.
27. Spathe tube green; ovules 1 per locule; posterior rib barely or not at all naked along the sinus (up to at most 2.5 cm); southwestern Costa Rica, ca. 1,000 m.
P. dominicalense Croat & Grayum

27. Spathe tube dark reddish to red-purple; ovules ca. 20 per locule; posterior rib naked to ca. 6 cm along the sinus; Costa Rica, principally on the Atlantic slope at 300-850 m and Ecuador at 200-1,500 m.
P. dodsonii Croat & Grayum

22. Peduncles usually more than 10 cm long. 28. Stems clothed with a dense series of overlapping cataphylls, each persisting as a dense reticulum of coarse fibers often overlain with a thin, fragmented epidermis. 29. Blades 1.2-1.5 times longer than wide; blades drying reddish brown above; Panama (Darién), 1,000-1,560 m.
P. pirrense Croat
29. Blades only slightly longer than wide or even wider than long (0.8-1.4 times longer than wide); blades drying grayish green above.  
30. Dried blades with lower surface semiglossy and sparsely granular, the upper surface lacking raphide cells; ovules 6 per locule; Panama, Panama Province (Cerro Jefe), 550-800 m.

P. jefense Croat
  30. Dried blades with lower surface matte, smooth and minutely brownish to whitish speckled, lacking obvious cross veins, the upper surface usually with short whitish raphide cells visible; ovules 14-20 per locule; Panama, Canal Area to Darién Province (Cerro Sapo), 140-800 m
P. lazorii Croat.

28. Stems with only a few cataphylls, usually these semi-intact or with a few, thin, disorganized fibers.

31. Blades drying reddish brown to dark yellow-brown; peduncles usually less than half as long as the spathe; spathe tube reddish purple to red; Costa Rica and Ecuador, 300-1,500 m.
P. dodsonii Croat & Grayum

31. Blades drying dark gray-brown to olive-green, typically somewhat blackened above; peduncles usually as long as or longer than the spathe, frequently bent just below the spathe; spathe tube greenish; Panama, 0-750 m
P. panamense K. Krause

1. Blades with posterior rib (union of basal veins) not naked along the sinus.  
32. Petioles conspicuously scaly near apex; terrestrial.
33. Blades less than 25 cm long; petiolar scales close and overlapping, broad, usually less than 3 times longer than wide; endemic to El Copé region of Panama, ca. 800 m.
P. hammelii Croat

33. Blades usually more than 30 cm long; petiolar scales more widely scattered, many times longer than wide.

34. Plants terrestrial; stem usually creeping laterally across ground; inflorescences glabrous; Mexico and Guatemala, 580-1,900 m.
P. glanduliferum Matuda var. glanduliferum

34. Plants appressed hemiepiphytic climbers; stems usually climbing trees; inflorescences conspicuously covered with slender scales, Costa Rica to Peru, 200-1,500 m (mostly >500 m.
P. verrucosum Mathieu ex Schott

32. Petioles glabrous and smooth toward apex, at least not conspicuously scaly; usually hemiepiphytic.  
35. Plants consistently terrestrial; petioles D-shaped with raised margins and a medial rib; spathe tube greenish to whitish within (usually reddish on western slope in Costa Rica); Nicaragua (Zelaya) to Panama, Colombia and Ecuador; mostly 0-750 m.

P. grandipes K. Krause
35. Plants usually hemiepiphytic (frequently terrestrial in some habitats for P. tysonii); petioles terete to subterete; spathe tube maroon to red or violet-purple within.  
36. Spathe not at all constricted above the tube, usually to ca. 1 cm thick midway; leaf blades very coriaceous, minor veins etched in the upper surface of fresh leaves; central Costa Rica to western Panama, 1,100-2,600 m.

P. crassispathum Croat & Grayum
36. Spathe visibly constricted above the tube (except only weakly constricted for P. antonioanum), usually less than 3 mm thick except at very base; leaf blades not markedly coriaceous, minor veins never etched into surface of fresh leaves.  
37. Primary lateral veins frequently 10 or more; spathe tube white to pale green within (sometimes tinged red at very base); Nicaragua to southern Ecuador and to Venezuela; 30-1,400 m.

P. tenue K. Koch
37. Primary lateral veins usually fewer than 10 (to 10 in P. tysonii); spathe tube red to red-violet, maroon, or violet-purple throughout within. 38. Blades markedly sinuate along the margins; Mexico (Veracruz), less than 500 m.
P. subincisum Schott
38. Blades with the margins not at all sinuate or otherwise lobed. 39. Fresh cataphylls usually red; petioles and midribs lacking conspicuous purplish spots. 40. Blades with primary lateral veins typically 6-10 per side, upper surface drying somewhat blackened and smooth; cataphylls unribbed to weakly 1-ribbed; spathe tube green or merely tinged reddish outside; ovaries with fewer than 7 sub-basal ovules contained in an ovule sac. western and central Panama, 600-1,430 m.
P. tysonii Croat
40. Blades with primary lateral veins usually 5-6 per side, upper surface drying dark brown to gray-brown with prominulous cross-veining; cataphylls sharply 2-ribbed; spathe tube bright maroon outside; ovaries with about 30 axile ovules not contained in an envelope; endemic to Veraguas and Coclé Provinces at 850-1,150 m.
P. antonioanum Croat
39. Fresh cataphylls green (purplish spotted in P. edenudatum and P. grayumii); blades drying yellow-brown to light reddish brown below; basal veins usually 3-5 per side; petioles and midrib frequently purplish spotted.   41. Blades mostly more than 1.8 times longer than wide; petioles 0.85-0.90 times as long as the blade; dried blades without secretory ducts visible on lower surface; Panama, 735-1,150 m.
P. edenudatum Croat
41. Blades mostly less than 1.8 times longer than wide; petioles 1-1.4 times longer than the blade; dried blades with secretory ducts clearly visible on the lower surface; Costa Rica to central Panama, 0-1,200 m.
P. grayumii Croat