Philodendron radiatum Schott,
Oesterr. Bot. Wochenbl. 3: 378. 1853. TYPE: Mexico (holotype lost). Schott ic. 2623 [neotype here designated]. Figures 1, 324, 331--335.
Epiphytic or hemiepiphytic, rarely terrestrial; stem appressed-climbing, creeping if terrestrial, sap clear to orange, watery, sticky, leaf scars conspicuous, 2--4(7.5) cm long, 2.5--6(7) cm wide; internodes thick, 3--7(12) cm long, (1)3--8 cm diam., about as long as broad or longer than broad, dark green to gray-green, sometimes scurfy and light brownish tan, transverally lined (raised 2 mm); roots 4 mm diam., with swollen nodes and branched tips; cataphylls to 38 cm long, soft, bluntly to sharply 2-ribbed, rarely unribbed, green, sometimes conspicuously reddish lineate, deciduous; petioles 283--108 cm long, (2-3)4--17 mm diam., terete or subterete to obtusely flattened adaxially, dark green, surface dark greenish or to greenish red-lineate; sheath persisting, sometimes moderately spongy; blades more or less triangular-ovate in outline, (15)27--101 cm long, (11)25--90 cm wide (ca. 0.8--2.1 times longer than wide) (0.5--1.7 times longer than petiole), broadest at point of petiole attachment, thinly coriaceous, weakly to moderately bicolorous, semiglossy, acuminate to long-acuminate at apex, upper surface dark green, lower surface slightly paler, usually drying yellow-brown to reddish brown on both surfaces; margins weakly incised-lobate to usually deeply incised-lobate to within 1--8 cm of midrib, rarely entire and sagittate; apex often acute, sometimes acuminate, very short acuminate or more or less rounded (the acumen tightly inrolled if present, 1--8 mm long), lobed-cordate at base; basal segments pinnatifid, lateral segments entire, sinnuate or the lowermost of the anterior lobe pinnately-lobed with 1--2 lobes on each side, final divisions linear-lanceolate in shape (0.9--2.1 times longer than wide), segment apex obtuse to broadly obtuse; interlobal sinuses 0.7--0.97 the length of the lobes; basal sinus hippocrepiform to obovate or closed, 3--15 cm deep; midrib slightly raised to convex, weakly reddish green-lineate, concolorous to paler than surface above, convex to prominently raised to round-raised below; basal veins 4--5(8) per side, directed into the segments of the posterior lobe, 0--1 free to base, (1)2--4 coalesced to 3 cm long, naked 1--6 cm; posterior rib absent; primary lateral veins 3--8 per side, departing midrib at a 50--60E angle, straight to margin, weakly raised above, raised to convex and paler than surface below; minor veins moderately visible, paler and slightly raised below, arising from both the midrib and primary lateral veins.
INFLORESCENCES erect, 1--3(4) per axil; peduncle 2--12 cm long, (3)5--10(19) mm diam.; spathe erect, 11--25 cm long (1.3--6.3 times longer than peduncle), obscurely striate, margins paler; spathe blade cuspidate at apex, pale green to yellowish green, semiglossy, sparsely purplish dotted outside, pink to dull red or pale brownish (post anthesis) inside; spathe tube dark purple-violet or dark green, sometimes tinged purple-violet outside, 4 cm diam., dark purple-violet inside; spadix sessile to weakly stipitate, cylindrical to weakly tapered; staminate portion creamy white, protruding forward at anthesis, pointed at apex, 10--17 cm long; pistillate portion whitish, weakly obovoid, 3.5--5.2 cm long (1 cm shorter on back side), 1.1--1.8 mm diam. at apex, 1.5--1.9 mm diam. at middle, (7)17 mm wide at base; staminate portion 6.3--8.1 cm long; fertile staminate portion tapered, 1--1.9 cm diam. at base, 1.2--1.6 cm diam. at middle, 0.9--1.4 cm diam. ca. 1 cm from apex, broadest at the base, slightly constricted above the base; sterile staminate portion as or slightly broader than the pistillate portion, white with tan ring around apex, 0.7--2 cm diam.; pistils (1.6)4--5(8) mm long, (1)2.8--3.2(5.2) mm diam.; ovary (7)8-locular, (1.6)3.3--4(6.7) mm long, 1.5--3(5.2) mm diam., with axile or sub-basal placentation; locules (0.6)1.9--3.4(6.5) mm long, 0.5--0.8(1) mm diam.; ovule sac 1.8(3.5) mm long; ovules 8 per locule, 1--2-seriate, contained within translucent, gelatinous ovule sac, 0.1--0.3 mm long, longer than funicle; funicle 0.1--0.2 mm long, style 0.3--0.5 mm long, 1.2--3 mm diam., similar to style type B (rarely C); style apex flat to weakly rounded, somtimes domed; stigma usually hemispheroid, sometimes subdiscoid, pink, 1.2--1.5 mm diam., 0.6--0.7 mm high, covering entire style apex; the androecium truncate, oblong, prismatic, margins irregularly 3--5-sided, sometimes weakly scalloped, 1 mm long, (0.7)2.5--2.7 mm diam. at apex; thecae cylindrical, 0.3 mm wide, more or less parallel to one another and contiguous; sterile staminate flowers usually truncate, sometimes clavate or irregularly 5--6-sided, 1.1--2.9 mm long, 0.6--1.8 mm wide.
INFRUCTESCENCE 11--17 cm long, 4.5 cm diam.; pistillate spadix 6--8 cm long, 2.5--3.5 cm diam.; berries white, somewhat translucent, 4 per locule, oblong, sticky.
Philodendron radiatum ranges from Mexico (San Luis Potosí to Chiapas and on both Atlantic and Pacific slopes in Chiapas) to Colombia (Antioquia), from sea level to usually no more than 700 m (rarely 1250 to 1860 m; most collections are from below 100 m) elevation. It is perhaps more widespread in South America than collections indicate (only two are known). The plants are very large and difficult to collect and may have been overlooked in other areas.
This species is highly variable morphologically and ecologically versatile as well. In Mexico, it occurs in "Selva Alta Perennifolia", "Selva Mediana" and "Selva Baja Caducifolia" in mesic areas on the Atlantic slope as well as in "Selva Mediana Subperennifolia" and "Selva Baja Subperennifolia" in the drier Yucatán Peninsula. On the Pacific slope it also occurs in areas of "Bosque Pino-Encino." In Central America, this taxon occurs principally in Tropical moist forest but also in Premontane wet forest and drier parts of Tropical wet forest.
Philodendron radiatum is a member of P. sect. Polytomium. Philodendron radiatum has two varieties, the typical variety having more deeply divided leaf blades with the segments often incised almost to the midrib and P. radiatum var. pseudoradiatum with the blades only weakly incised-lobate (less than half the distance to the midrib). While the latter variety is restricted to southwestern Chiapas, even populations of the typical variety on the western slope of Central America, have less deeply incised-lobate blades than those on the Atlantic slope. There is also considerable clinal variation in the width of the divisions throughout Central America, with plants in Mexico having, on average, broader pinnae (averaging 4.5 cm wide) than those in Panama, for example, where the pinnae average only about 3 cm wide. Leaves of Mexican populations of P. radiatum also consistently lack free basal veins, whereas elsewhere in Central America such veins are present. In western Mexico and Guatemala, plants are also more likely to have longer internodes and to occur more frequently on rocks or creeping over the ground than plants on the more mesic Atlantic slope of Central America).
Key to the varieties of P. radiatum:
A. Blades deeply lobed, the divisions near the middle of the blade extending more than 3/4 the way to the midrib. var. radiatum
A. Blades shallowly lobed, the divisions near the middle of the blade extending less than 1/2 the way to the midrib. var. pseudoradiatum (Matuda) Croat