KEY TO THE SPECIES OF SYNGONIUM

Ia. Leaf blades not divided into segments.

2a. Leaf blades oblong-elliptic or ovate-elliptic, merely rounded to subcordate at the base; petioles sheathed nearly their entire length.

3a. Blades mostly less than 15 cm long; primary lateral veins arising from the lower half of the blade. __ 1. S. armigerum
3b. Blades commonly more than 15 cm long; primary lateral veins uniformly distributed along the blade.

4a. Petioles 9-33 cm long, the sheath 2-3 cm wide (when flattened), usually extending over the base of the blade, rounded at the apex; blades 13-34 cm long; peduncle 6-8 cm long (to 10 cm long in fruit); fruiting spathe tube 8-10 cm long - --- 2. S. llanoense
4b. Petioles 6-10 cm long, the sheath less than 1 cm wide (when flattened), usually ending well below the base of the blade, acute at the apex; blades 14-23 cm long; peduncle to 4 cm long (in fruit); fruiting spathe tube ca. 4 cm long -3. S. oduberi

2b. Leaf blades ovate to hastate or sagittate, conspicuously lobed at the base; petioles sheathed 1/3-3/4 their length.

5a. Stems glaucous; juvenile blades thick, cordate; adult blades thick, the veins not prominent.---------------- 4. S. chiapense
5b. Stems not glaucous; juvenile blades thin, often hastate or sagittate; adult blades thin, the veins prominent.

6a. Adult blades markedly hastate with pronounced, pointed, posterior lobes directed outward at ca. 45' angle, the anterior lobe somewhat constricted at the base-- 10. S. hastifolium
6b. Adult blades ovate, oblong-ovate or elliptic-hastate, not markedly hastate, the posterior lobes rounded or, if pointed, then much smaller than the anterior lobe, usually directed mostly downward, the anterior lobe usually not markedly constricted at the base (except A. hastiferum).

7a. Blades with the lower surface pale, matte, whitish; basal veins fusing to form a posterior rib more than 3 cm long; Costa Rica and Panama --- 13. S. schottianum
7b. Blades with the lower surface semiglossy or matte but never whitish; basal veins forming a distinct posterior rib or nearly free to the base.

8a. Blades elliptic-hastate, usually weakly or strongly constricted between the anterior and posterior lobes, the posterior lobes usually narrowly angular; Costa Rica ------------ 9. S. hastiferum
8b. Blades ovate or oblong-ovate, not constricted between the anterior and posteriorm lobes, the posterior lobes rounded or obtuse, not acutely angular; Mexico or South America and western Panama.

9a. Blades lacking a well-developed posterior rib (united basal vein), the posterior
rib lacking or less than 1 cm long, the basal veins all or nearly all submarginal
to the sinus; spathe tube less than 5 cm long at anthesis.

10a. Blades broadest at the base or in the lower third; primary lateral veins 5
9 pairs, unbranched; tertiary veins distinct, irregular and wavy, relatively
remote from one another; western Venezuela --11. S. meridense
10b. Blades broadest at about the middle; primary lateral veins 9-15 pairs, with
distinct branches at least in the lower part of the blade; tertiary veins ob
scure, regular and closely parallel; northern Colombia (Choco) --- 5. S. chocoanum

9b. Blades with a well-developed posterior rib usually more than 1 cm long, the
posterior rib naked for some distance from the apex of the sinus; spathe tube
usually 6.5-15 cm long at anthesis; northern South America or Mexico.

11a. Blades less than 35 cm long; primary lateral veins in 3 or 4 pairs; spadix
less than 8 mm diam. at the broadest point; northern Colombia (Choco).
-------- 8. S. foreroanum
11b. Blades mostly more than 35 cm long; primary lateral veins in 9-13 pairs;
spadix 1-2.5 cm diam. at the broadest point.

12a. Spathe blade long-acuminate at the apex; northern Oaxaca (Mexico).--- 12. S. sagittatum
12b. Spathe acute or short-acuminate at the apex; Colombia, Ecuador and Venezuela.

13a. Blades dark green, thin (drying blackened and papyraceous); primary lateral veins red, in moderately deep valleys; tertiary veins distinct on drying; spathe tube elliptic, light orange-red, conspicuously constricted at the apex, the blade light orange-red throughout -------- 7. S. dodsonianum
13b. Blades subcoriaceous, light green, drying chartaceous, greenish brown; primary lateral veins green, not markedly sunken in valleys; tertiary veins moderately obscure on drying; spathe tube oblong-elliptic, medium green, only moderately constricted at the apex, the blade creamy white throughout. --6. S. crassifolium

1b. Leaf blades either trilobed, trisect, 5-1 I-pedatisect or incised-lobate.

14a. Blades incised-lobate; Guatemala and Mexico---- 14. S. steyermarkii
14b. Blades trilobed, trisect or 5-1 I-pedatisect.

15a. Spathe tube cylindroid, frequently more than 6 cm long; spathe blade usually twice as long as the staminate part of the spadix; fruiting spadix elongate, + - cylindroid; West Indies --- 17. S. auritum
15b. Spathe tube usually ellipsoid or ovoid (oblong-ovoid in S. atrovirens), rarely more than 6 cm long (to 8 cm in S. neglectum, to 7 cm in S. atrovirens and S. chiapense); spathe blade usually only slightly longer than the staminate part of the spadix; fruiting spadix + - ellipsoid; Central and South America and Trinidad.

16a. Adult blades trisect or trilobed, sometimes appearing almost 5-parted because of conspicuous auricles on lateral segments.
17a. Blades with the lateral segments merely inequilateral, not markedly auriculate or if markedly auriculate, the auricle at least not pinched off to appear like another segment.
18a. Median lobe of the adult blade with the primary lateral veins departing the midrib at almost 90' angle (rarely at less than 65' angle).

19a. Lateral leaflets scarcely unequal at the base, not at all auriculate; Ecuador
on the Atlantic slope ---- 29. S. sparreorum

19b. Lateral leaflets noticeably unequal at the base, sometimes + - auriculate; Central and South America.

20a. Primary lateral veins of the median leaflet indistinct, scarcely more prominent than the lesser veins; Costa Rica and Panama ----------- 23. S. laterinervium

20b. Primary lateral veins of the median leaflet distinct, much more prominent than the lesser veins; South America. 21a. Spathe tube narrowly oblong-ovoid, 5.5-7.2 cm long, scarcely constricted at the apex; western Venezuela.--- 16. S. atrovirens 21b. Spathe tube oblong-elliptic, 3-3.5 cm long, conspicuously constricted at the apex; western Amazon Basin, Brazil, Peru and Bolivia ----- 33. S. yurimaguense

18b. Median lobe of the blade with the primary lateral veins in the lower third of the leaflet sharply ascending, departing the midrib at usually less than 60' angle.

22a. Lateral segments of the adult blade with a conspicuous, usually + - hastate auricle.

23a. Young leaves, peduncle and spathe tube pruinose; leaves 30-45 cm wide; highland species occurring in wet forest at elevations above 1300 m in Chiriqui (western Panama) and Costa Rica ------------- 20. S. glaucopetiolatum

23b. Young leaves, peduncle and spathe tube not pruinose; leaf blades less than 25 cm wide (rarely to 35 cm wide in S. salvadorense); principally lowland species occurring below 700 m, primarily in tropical forest on the Pacific slope from Chiapas, Mexico, and Guatemala to Panama.

24a. Peduncle 9-18 cm long (to 25 cm long in fruit); leaf blades with 3-5 primary lateral veins on each side, these mostly restricted to the lower half of the blade; stems usually pruinose; southern Mexico to El Salvador -28. S. salvadorense
24b. Peduncle 3.5-9 cm long; leaf blades with 6 or more primary lateral veins on each side, + - equally distributed throughout the blade; stems not pruinose; Costa Rica and Panama .--------25. S. mauroanum

22b. Lateral segments not prominently auriculate or, if auriculate, the auricle at least not at all hastate.

25a. Leaf blades merely trilobed with the segments markedly confluent and less than 12 cm long (confluent in S. chiapense and S. podophyllum but these have a median lobe more than 16 cm long); rare species from Ecuador ------------ 21. S. harlingianum
25b. Leaf blades with usually 3 distinct leaflets (except S. chiapense, usually unlobed, and sometimes S. podophyllum.

26a. Lateral segments with the auricles moderately conspicuous and directed downward, more or less in line with the midrib of the segment; stems, petioles and peduncles glaucous or the segments silky due to conspicuous papillae on the upper surface; spathe tube dark red inside.

27a. Stems, petioles and peduncles glaucous; blades not silky
pubescent due to papillae on the surface. 22. S. hoffmannii
27b. Stems, petioles and peduncles not glaucous; blades silky
on the upper surface due to papillae. ---- 32. S. wendlandii

26b. Lateral segments with auricles conspicuous or not, but usually not directed downward more or less in line with the midrib of the segment; plants lacking silky upper blade surfaces; plants usually not glaucous or if glaucous, the lateral segments definitely lacking conspicuous auricles, spathe tube variously colored within.

28a. Lateral leaflets narrowly acute to attenuate at the base, not the least auriculate.

29a. Inflorescence solitary; stems less than 1 cm diam., densely and minutely papillate; below 500 m, Honduras to Costa Rica - ------------ 30. S. standleyanum
29b. Inflorescences paired; stems ca. 2 cm diam.,smooth; above 1000 m elevation, Peru -------- 19. S. gentryanum

28b. Lateral leaflets usually conspicuously inequilateral and auriculate (or at least with the outer margin broadly rounded).

30a. Leaf blades thin, the veins conspicuously sunken (when fresh).

31a. Median leaflet with 5-9 pairs of primary lateral veins, drying greenish brown; juvenile blades sagittate; inflorescences 1 or 2 per axil; tropical moist and premontane moist forest, Costa Rica and Panama.---- 25. S. mauroanum
31b. Median leaflet with 10- 16 pairs of primary lateral veins, drying black; juvenile blades elliptic; inflorescences 1-5 per axil; tropical wet and premontane wet forest, Honduras to Panama - ---------------------------- 31. S. triphyllum

30b. Leaf blades moderately thick to coriaceous, the veins not conspicuously sunken.

32a. Blades mostly less than 20 cm long, the lateral leaflets mostly narrowly rounded at the apex; juvenile leaves purplish violet on the lower surface; adult blades and stems drying conspicuously brown; tropical moist and premontane wet forest, central Panama ---- 18. S. erythrophyllum

32b. Blades mostly more than 20 cm long (sometimes less in S. standleyanum and S. mauroanum), the lateral leaflets usually acute at the apex; juvenile leaves green beneath; adult blades and stems drying mostly green to black (the stems sometimes drying brown).

33a. Peduncles 1-3 per axil, usually more than 9 cm long, frequently 14-25 cm long in fruit.

34a. Juvenile blades broadly ovate-cordate; adult blades thick, the median segments 28-52 cm long, the lateral segments smaller (10-20 cm long), directed nearly backwards; peduncle and spathe tube blue glaucous; Mexico (Chiapas, mostly eastern, and southern Veracruz) - ---------------- 4. S. chiapense
34b. Juvenile blades hastate or sagittate; adult blades thin, the median lobe less than 28 cm long, the lateral segments not markedly smaller, mostly directed forward; peduncle and spathe tube green; southwestern Mexico (Chiapas) and western Guatemala to Costa Rica - -------------- 28. S. salvadorense

33b. Peduncles 4-11 per axil, usually less than 9 cm long, to 13 cm long in fruit. ---27a. S. podophyllum var. podophyllum

17b. Blades with the lateral segments bearing conspicuous auricles, these pinched off to appear like separate segments (some leaf blades of S. triphyllum with the lateral segments not pinched off).

35a. Stems with large, elongate projections. ----27b. S. podophyllum var. peliocladum
35b. Stems lacking elongate projections.

36a. Upper blade surface silky due to papillae; Costa Rica.---- 32. S. wendlandii
36b. Upper blade surface lacking papillae.

37a. Median leaflet with 10-16 pairs of prominently sunken primary lateral veins; spathe tube red inside ----- 31. S. triphyllum
37b. Median leaflets with usually fewer than 8 pairs of primary lateral veins, these not conspicuously sunken; spathe tube green or red to violet purple inside.

38a. Spathe tube red to violet purple inside; inflorescences 1-4 per axil, usually no more than 3; blades usually drying black; tropical wet, premontane wet or more commonly lower montane rainforest, Costa Rica to Panama - 22. S. hoffmannii
38b. Spathe tube green inside; inflorescences 4-11 per axil; blades usually drying green.

39a. Stems not glaucous, sometimes with numerous rough emergences; leaf segments usually slender, of nearly equal size and shape; petioles subterete, usually with a sharp medial rib; rachis usually gradually curved, not angular between each segment; staminate flowers deeply retuse at the apex, showing no indication of the line of fusion; Mexico to Costa Rica - ---------- 15. S. angustatum
39b. Stems glaucous (at least in northern Central America), smooth, lacking any emergences; leaf segments usually somewhat unequal, not of relatively uniform size and shape; petioles subterete or with only an obtuse medial rib; staminate flowers truncate at the apex with an indication of the line of fusion; Mexico to Panama.-------------------- 27a. S. podophyllum var. podophyllum

16b. Adult blades either 5-1 I-pedatisect or incised lobate (i.e., the segments of the anterior
lobe pinnate).
40a. Stems with conspicuous, elongate, projections; sea level to 1000 m, Costa Rica and Panama on the Atlantic slope (AlaJuela to Bocas del Toro) -------------------------------------------------------------------------- 27b. S. podophyllum var. peliocladum
40b. Stems lacking conspicuous, elongate projections; geographical ranges various.

41 a. Peduncles usually 1 (sometimes 2 or 3); entire inflorescence usually 20-40 cm
long (or in S. mauroanum less than 20 cm long with the leaf blades thin and with many sunken veins); spathe tube not glaucous; staminate part of the spadix 8.5-14 cm long (or less in S. mauroanum); Mexico, Costa Rica and Panama.

42a. Inflorescence less than 20 cm long; staminate part of the spadix less than
8 cm long; stems less than 1.5 cm diam.; premontane moist forest, west
ern Panama and Costa Rica --------------- 25. S. mauroanum
42b. Inflorescence usually more than 20 cm long; staminate part of the spadix
more than 8 cm long; stems more than 1.5 cm diam.; blades chartaceous,
the veins not sunken; not occurring in premontane moist forest, Mexico.-------------------------------26. S. neglectum
41b. Peduncles usually numerous (unless collected when flowers are first beginning
to develop); entire inflorescence usually less than 20 cm long; spathe tube often
glaucous; staminate part of spadix 2.5-9 cm long; Mexico to Ecuador, Brazil
and Bolivia.

43a. Adult leaf blades thick, the upper surface very smooth, the median leaflet
often more than 35 cm long; juvenile blades thick, large, cordate; peduncles 10-20 cm long; spathe tube usually glaucous, even in fruit; mature infructescence usually more than 10 cm long, 5-8 cm wide --------- 24. S. macrophyllum
43b. Adult leaf blades thin, the upper surface not smooth, the median leaflet
usually less than 35 cm long; juvenile leaves thin, sagittate or hastate (or
if cordate, very small); peduncles less than 10 cm long at anthesis; spathe
tube usually not glaucous in fruit; mature infructescence usually less than
10 cm long, 4.5 cm wide.

44a. Stems not glaucous, sometimes with numerous rough emergences;
leaf segments usually slender, of nearly equal size and shape; pet
ioles subterete, usually with a sharp medial rib; rachis usually grad
ually curved, not angular between the segments; staminate flowers
deeply retuse at the apex, showing no indication of the line of fusion;
Mexico to Costa Rica ----------------- 15. S. angustatum
44b. Stems glaucous (at least in northern Central America), smooth,
lacking any emergences; leaf segments usually somewhat unequal,
not of relatively uniform size and shape; petioles subterete or with
only an obtuse medial rib; staminate flowers truncate at the apex
with an indication of the line of fusion; Mexico to Panama.-- 27a. S. podophyllum var. podophyllum