Usually hemiepiphytic, rarely terrestrial or epilithic; stem appressed-climbing, parchment-white, sap turning blackish, slimy; internodes usually terete, weakly angular, sometimes obscurely flattened on one side or closely and acutely ribbed, semiglossy to matte, 1-20 cm long, 1.5-4 cm diam., dark green, becoming usually gray-green to brown, sometimes pale yellow-green, epidermis somewhat ridged ("wrinkled"), sometimes fissured transversely; roots reddish brown, 6÷10 mm long, 3÷5 mm diam., arising from and along the node on one side; cataphylls 18÷39 cm long, usually weakly 1-ribbcd, sometimes unribbed or weakly to sharply 2-ribbed or sharply 1-ribbed (ribs to 1 cm high), soft, green, sometimes reddish to pinkish, sometimes sparsely green-spotted, purple-maroon or darker striate near base, drying reddish brown, margins sometimes prominently and thinly raised, usually soon deciduous, rarely persisting as a rotting mass, rounded at apex; petioles 20-65(91) cm long, 3-15 mm diam., usually subterete, moderately spongy to firm, medium green, drying greenish brown, obtusely flattened, usually obtusely and narrowly sulcate, rarely obtusely and broadly sulcate adaxially, surface minutely and densely short purple- or occasionally white-striate, sometimes dark green or violet-purple blotched, sometimes smooth to irregularly ribbed and folded; sheath subtending an inflorescence, 5÷8 cm long; blades ovate to ovate-triangular, semiglossy, moderately coriaceous, weakly to moderately bicolorous, acuminate to narrowly acuminate, sometimes short-acuminate at apex, prominently cordate to ± sagittate at base, 30÷72 cm long, 15÷39 cm wide (1.85-2 times longer than wide), (0.6÷1.6 limes longer than petiole), margins somewhat hyaline, weakly revolute, upper surface medium green, drying brownish green to greenish brown, semiglossy, lower surface pale yellow-green, sometimes reddish, drying usually reddish brown, sometimes yellowish brown, weakly glossy to matte; anterior lobe 24÷61 cm long, 13-34.5 cm wide (2÷5.1(5.5÷6.4) times longer than posterior lobes); posterior lobes usually narrowly rounded, 6-20.5 cm long, 5-17.6 cm wide; sinus ± V-shaped to almost closed, 6÷15 cm deep; midrib flat to weakly raised, paler than surface, drying broadly raised and ± concolorous above, convex to narrowly raised, sometimes maroon-spotted or with white flecks, concolorous to darker than surface, drying broadly raised and reddish below; basal veins 3-5(6) per side, with 0÷1(2) free to base, third and higher order veins sometimes coalesced 2.5÷4.5 cm, a few additional veins sometimes coalesced to 6.5 cm; posterior rib not at all naked or only briefly so; primary lateral veins 4÷9 per side, departing midrib al a 60÷70¡ angle, weakly curved to the margins, but usually turned prominently up just before the margin, rather prominently downtumed just before the midrib, round-raised to flat to obtusely sunken and paler than surface above, convex, concolorous to darker than surface below; interprimary veins weakly sunken, concolorous above, flat, darker than surface below; minor veins weakly visible below, arising from both the midrib and primary lateral veins, drying moderately prominent, weakly undulate, alternating with dark, mostly contiguous secretory ducts.

INFLORESCENCES erect, 1-3 per axil; peduncle 4-15 cm long, 1.6-1.8 cm diam., somewhat flattened to terete, green, sometimes tinged reddish, drying greenish, densely short and broad striate; spathe 8-22 cm long, 2-3 cm diam. (0.8-2.2 times lunger than peduncle), weakly to obscurely constricted above the tube, semiglossy, usually green, sometimes plum-red, often purple-spotted, densely short pale lineate throughout, weakly so near apex, blunt to narrowly cuspidate-acuminate to prominently acuminate, frequently tinged purplish violet at base; spathe blade green to pale yellow-green, 8÷11 cm long (opening 3-4.3 cm wide, sometimes opening to near the base), greenish white, weakly tinged red-purple in throat to pale yellow-green or white inside, sometimes reddish throughout in age; resin canals appearing as continuous lines, red-purple to orange in color, spathe tube green, sometimes moderately to heavily tinged red-purple to red (B & K red-purple 3/7.5), with sparse, dark purplish spots (mostly medially) throughout outside, 4÷7 cm long, 2.5÷3.5 cm diam., red to reddish purple (B & K red-purple 3/7.5), white striate inside; spadix stipitate to 7 mm long; tapered toward apex, (8)9÷16 cm long, broadest below the middle or near the base, usually protruding somewhat forward at anthesis but not curved; npistillate portion pale green (anthesis) to greenish white to yellow-green (post-anthesis), uniformly wide throughout or weakly tapered toward both ends, 2.5÷ 6.2 cm long in front, 2-A.7 cm long in back, 1-1.2 cm diam. at apex, 1.1-1.7(2.1) cm diam. at middle, 1.1÷1.7 cm wide at base; slaminate portion 6.3÷ 10.3(13) cm long; fertile staminate portion usually creamy white, sometimes pale green to pinkish, 9-13 mm diam. at base, 11-13 mm diam. at middle, 8÷10 mm diam. ca. 1 cm from apex, broadest at base or middle, about as broad as the pistillate and sterile portions; sterile staminate portion often broader than the pistillate portion, white, (0.9-1)1.2-1.9 cm diam.; pistils (0.9)1.8-4.4 mm long, (0.9)1.3-2.3 mm diam.; ovary 6÷9-locular, 1÷1.7(3) mm long, 1.3÷2.3 mm diam., with sub-basal placentalion; locules 1-1.7(3) mm long, 0.2-0.4 mm diam.; ovule sac (0.6)0.8-1.2 mm long; ovules usually 2-4, rarely 5÷ 8 per locule, 1-seriate (2-seriate, if 4 or more ovules), usually contained within translucent, gelatinous ovule sac, sometimes contained within gelatinous matrix (no true envelope), 0.1÷0.5 mm long, usually longer than funicle; funicle 0.1÷0.3 mm long (can be pulled free to base), sometimes adnate to lower part of partition, style (0.4)0.6-0.8 mm long, (0.8)1.2-1.6 mm diam., similar to style type B; style apex flat to sloping; stigma discoid or subdiscoid. truncate, (0.7)1-1.5 mm diam., (0.1)0.3-0.5 mm high, covering entire style apex, sometimes shallowly depressed at middle; the androecium truncate, prismatic, oblong, margins irregularly 4-6-sided to weakly ovate, ca. 1 mm long, 1.6-2 mm diam. at apex; thecae oblong, 0.4÷0.6 mm wide, ± parallel to one another, sometimes contiguous; sterile staminate flowers blunt, irregularly 4-6-sided, sometimes clavate or prismatic, 1.4^-2.1 mm long, 1.4÷2 mm wide.

INFRUCTESCENCE pink, green at base with reddish spots outside; berries pale yellowish, rarely orange, with stigmas reddish brown, 7 mm long; seeds 2÷3 per locule, drying pale brown to tannish brown, narrowly ellipsoid to oblong-ellipsoid, 1.4-2 mm long, 0.7-0.9 mm diam., with faint striations.

Flowering in Philodendron sagittifolium occurs almost throughout the year, principally after the onset of the dry season and continuing throughout much of the rainy season. There is a slight geographical shift, with flowering beginning about one month earlier in Mexico and Guatemala (January through August, less frequently in September and October) and continuing somewhat longer in Panama (February through September, but also rarely in December). Fruits apparently mature in about two months' time, but mature fruits have seldom been collected, only from January and July.

Philodendron sagittifolium ranges from Mexico (Veracmz) to Colombia (and probably also to Venezuela), from sea level to 1800 m elevation. It is probably the most morphologically variable, and one of the most ecologically versatile, species in Central America. In Mexico, this species occurs in "Selva Alia Perennifolia," "Selva Mediana Subper-ennifolia," "Selva Baja Caducifolia," and "Bosque Caducifolio." In the remainder of Central America, it occurs principally in Tropical moist forest and Premontane wet forest, but also in Premontane rain forest and Tropical wet forest life zones.

Philodendron. sagittifolium is a member of P. sect. Calostigma subsect. Macrobelium ser. Macrobelium. This species, though highly variable in most regards, can be characterized by its ap-pressed-climbing habit; short, stout internodes; sharply two-ribbed, deciduous cataphylls; obtusely flattened, firm petioles usually spotted with violet-purple; and ovate-triangular, moderately coriaceous blades with the posterior rib not at all or only briefly naked along the sinus. Also characteristic is the externally green, frequently purple-spotted spathe, which is reddish purple on the tube within. In Mexico and Guatemala, Philodendron sagittifolium, is most easily confused with P. advena and P. purulhaense, differing from both in having the blades somewhat triangular and drying reddish brown rather than generally ovate and drying blackened. See P. advena for additional discussion.

In Panama, P. sagittifolium may sometimes be confused with P. annulatum, which differs in having the petioles somewhat spongy with a purple distal ring, blades typically ovate-oblong, and spathes commonly white on the blade portion. It can be confused at some stages of development with sterile specimens of P. bakeri.

Considering the highly variable nature of this species there are many noteworthy collections, only a few of which can be discussed here. Whitefoord & Eddy 222 from Panama has the lower blade surfaces drying yellowish brown rather than reddish brown and spathe solid plum-red oulaide. Also noteworthy is Hammel el al. 14598, which reports fruit color to be orange.

A few collections from Puntarenas Province, Costa Rica [Croat 57243, 67697, Crayum & Hammel 10066), differ in having the primary lateral veins paler, rather than darker on the lower surface. Sterile specimens from Cocos island (W. Klawe s.n., Foxier 4177) diller in having the minor veins minutely raised on the upper surface. These specimens may prove to represent distinct species. A large number of sterile and ostensibly juvenile collections from Nicaragua are of uncertain identity. One series, including Pipuly 3826, 4055, 5144, Stevervs 7628, 12673, 12739, may ultimately prove to be P. bakeri. Two other collections (Pipoly 5190, 5194) might prove to be still another species. Croat 60804, from the coastal Cordillera of Venezuela, reported as P. cf. sagittifolium (Croat & Lambert, 1986) is eillier this species or a very close relative. When Regel described P. sanguineum Regel, he cited no specimens or country of origin, but Krause (1913) cited a collection he had prepared from the Berlin Botanical Garden ol a cultivated Karwinsky collection from Cordoba in Veracruz State, Mexico. While no such collection still exists, Karwinsky collected in Mexico only a few years (1840÷1843) before Regel described P. .wnguineum. Thus it is possible that both Regel and Engler could have been dealing with the same material originally collected by Karwinsky at Cordoba.

Another synonym that deserves mention is P. lancigerum Standl. & L. 0. Williams, corresponding to a narrow-leaved form of P. sagittifolium restricted to the Pacific lowlands of Costa Rica. Ep-itypification was necessary because the type specimen (Alien 5612) consists of only an inflorescence.