Philodendron mexicanum Engl.
in Mart., Fl. Bras. 3(2): 143. 1878. TYPE: Mexico. Veracruz: vic. of Córdoba, Bourgeau 2176 (holotype, P; isotype, G). Figures 285--288.
Philodendron latisagittium Matuda, Anales Inst. Biol. Univ. Nac. México 22: 371, Fig. 2. 1951. TYPE: Mexico. Chiapas: Mpio. Siltepec, Cascada, mixed humid forest, over humid rocks, 1200 m, 4 Mar. 1951, Nakamura 31 (holotype,MEXU).
Usually hemiepiphytic, sometimes terrestrial or epilithic; stem scandent, leaf scars conspicuous, 1--1.5 cm long, 1.3--1.6 cm wide; internodes scurfy, glaucous to semiglossy, 18--21 cm long, 1--2 cm diam., longer than broad, medium green to gray-green, epidermis blistering, fissured more or less transversely; roots branched at tips, sometimes with swollen nodes along length; cataphylls fleshy, 10--23 cm long, unribbed or bluntly 1-ribbed, pale green, glossy, drying yellowish tan to yellowish green, deciduous intact; petioles 22--66.5 cm long, 2--13 mm diam., terete, moderately spongy, medium green, somewhat flattened adaxially, surface semiglossy; blades narrowly triangular-sagittate to triangular-hastate, subcoriaceous, acuminate to long-acuminate at apex, sagittate to hastate at base, 23--46 cm long, 14--38 cm wide (1.3--2.7 times longer than wide), (0.6--1.5 times longer than petiole), about equal in length to petiole, margins weakly undulate, upper surface dark green, drying dark brownish green, semiglossy, lower surface drying yellowish green, weakly glossy, paler; medial lobe 19--38 cm long, 8--20 cm wide (1.7--2.7 times longer than posterior lobes), usually 3--3.5 times longer than wide (rarely to 1.7 times longer than wide); posterior lobes 7--19.5 cm long, 4--12.6 cm wide, directed somewhat toward the base, rounded to rarely rounded; sinus parabolic to hippocrepiform or spathulate; midrib broadly sunken, concolorous above, convex, sparsely orange-spotted, slightly paler than surface below; basal veins 0--1(2--5) per side, with 0--1(2--5) free to base, or 1 coalesced, the third and fourth coalesced 3.6--4(13) cm; posterior rib not naked or naked for 0.5--2 cm, directed straight toward the tip of the blade and remaining 1.5--3.5 cm distant from blade margin; primary lateral veins (2)4--5(6) per side, departing midrib at a 55--65E angle, more or less straight to the margins, weakly sunken above, raised below; minor veins moderately distinct below, arising from both the midrib and primary lateral veins. INFLORESCENCES 1 per axil; peduncle 4--15 cm long, 4--12 mm diam.; spathe glossy, 8--16.5 cm long, 1.9--2.3 cm diam. (0.8--1.4(1.5--2.4) times longer than peduncle), acute at apex, the margins paler to clear within; spathe blade greenish to whitish outside; resin canals pale range and appearing as continuous lines inside; spathe tube greenish, sometimes pale reddish tinged outside; red-violet to maroon (B & K Red-Purple 5/7.5) inside; spadix sessile; bluntly rounded to somewhat acute at apex, 10.5--14.7 cm long, broadest toward the apex, constricted below the middle of fertile staminate portion; pistillate portion pale green to green to pale yellow, cylindrical to obovoid, 2-6 cm long, 1 cm diam. at apex, 1.1 cm diam. at middle, 1.3 cm wide at base; staminate portion (6.4)10.3--12.7 cm long; fertile staminate portion creamy white, more or less cylindrical, 6--17 mm diam. at base, 7--15 mm diam. at middle, 1.1 cm diam. ca. 1 cm from apex, about as broad as the pistillate and the sterile portions; sterile staminate portion usually broader than the pistillate portion, white to light gray, 1--1.2 cm diam.; pistils 1.6--2(3.5) mm long, 1.1--1.3(2.6) mm diam., transparent white; ovary 5--7-locular, 0.9--2.7 mm long, 1.2--1.4(2.3-2.6) mm diam., with sub-basal placentation; locules 0.9--1.1(2.5) mm long, 0.2--0.4(0.6--0.7) mm diam.; ovule sac 0.6--0.7 mm long; ovules 1--2(3) per locule, digitate, contained within transparent ovule sac, 0.3--0.6(1.1) mm long, longer than funicle; funicle 0.3 mm long, style 0.7(1) mm long, 1.2--1.5(2.4) mm diam., similar to style type B; style apex domed; stigma discoid, at least sometimes lobed both laterally and vertically, sometimes more or less cylindrical, 0.7--1.0 mm diam., 0.1--0.3 mm high, covering center of style apex, at least sometimes drying with radial arms sunken between the central peak and the peaks on the end of the arms (Croat & Hannon 64520); the androecium truncate, margins irregularly 4--6-sided; thecae more or less cylindrical, 0.3--0.4 mm wide, more or less parallel to one another; sterile staminate flowers bluntly or acutely 4--6-sided, 1.3--1.9 mm long, 1.3--1.8 mm wide. INFRUCTESCENCE with seeds 1 per locule, yellowish orange, 1.5--1.9 mm long, 0.6--0.8 mm diam.
Flowering in Philodendron mexicanum occurs in the mid-dry season and early rainy season (February through May), with post-anthesis collections known February through June (except May) and also in November. Mature fruits are not known. A cultivated collection at Missouri Botanical Garden (Croat 59933) flowered perhaps twice per year, in March and in October.
Philodendron mexicanum ranges from Mexico to Colombia, from near sea level to 1900 m elevation, ranging from dry habitats in west-central Mexico (both "Selva Baja Caducifolia" and "Bosque Pino-Encino") to more humid sites on the Atlantic slope in Vera Cruz to as far south as Honduras in Tropical moist forest and to Costa Rica in Premontane wet forest. Though widespread, this species is apparently rare and has been collected from relatively few localities, often restricted to mesic enclaves in otherwise arid regions as in the state of Morelos, Mexico. It is one of the most ecologically versitile species in the genus.
Philodendron mexicanum is a member of P. sect. Calostigma subsect. Macrobelium ser. Macrobelium. This species is recognized by its scandent habit, internodes longer than broad, unribbed, deciduous cataphylls, moderately spongy, somewhat flattened petioles (about as long as the blades), and especially by its narrowly triangular-sagittate to triangular-hastate blades which dry dark brownish green above and yellowish green below. Sterile collections from Los Ríos and Guayas Provinces of Ecuador (Dodson & Valverde 6959) at Jauneche and in Guayaquil Cantón (Rubio et al. 2008) may also represent this species. Dodson et al. (1985) erroneously reported the former collection as P. barrosoanum G. S. Bunting, a species restricted to the eastern side of the Andes.
Philodendron mexicanum is most similar to P. angustilobum, a species ranging from Honduras to Panama. The latter species differs in having leaves that dry more blackened (rather than green to yellow-green as in P. mexicanum), and which are more decidedly three-lobed with the medial lobe proportionately narrower and broadest at the middle or even above the middle.
Although the type specimen of P. mexicanum was collected in Mexico near Córdoba, most Mexican collections are from the Pacific slope. These have somewhat less prominently narrowed posterior lobes than the type. Moore & Bunting 8873, from near the type locality, has the posterior lobes even more conspicuously narrowed than those of the type specimen. In this regard, its blades approach those of P. angustilobum in overall shape, but differ in drying greenish to yellowish brown rather than blackened.
A collection from Olancho Department, Honduras (Croat & Hannon 64520) is unusual in having a style that dries with radiating arms from a central peak.
The sole Costa Rican collection (Grayum 5418) is unusual in having prominently hastate blades. This collection has only a juvenile inflorescence. Further collections may prove it to represent a distinct species.
Additional specimens examined.
COSTA RICA. Puntarenas: Río Guacimal downstream from Monteverde, Cordillera de Tilarán, 1300 m, 10E18'N, 84E49'W, Grayum 5418 (MO). GUATEMALA. Quezaltenango: Finca Pireneos--Patzulín, 1200--1400 m, Standley 86917 (F); 87007 (F); 87022 (F). San Marcos: Volcán Tajumulco, 1300--1500 m, Steyermark 37968 (F). HONDURAS. Atlántida: Quebrada Grande, ca. 10 km SW of La Ceiba, 80--180 m, 15E42'N, 86E51'W, Liesner 26138 (MO). Olancho: San Esteban--Bonito Oriental, Río Grande, 350--400 m, 15E31'N, 85E42'W, Croat & Hannon 64520 (B, CAS, CM, CR, HNMN, K, L, MEXU, MO, NY, USCG). Yoro: Puente Grande, Río Puente Grande (tributary of the Río Agua), Blackmore & Chorley 4077 (BM, MO). MEXICO. Cultivated at Cornell University, Ithaca, New York, Moore 7437 (BH); Ixtapan de La Sal, 1900 m, 18E50'N, 99E41'W, Matuda et al. 32130 (MEXU). Guerrero: Atoyac region, above Fila de Caballo, El Paraíso in Parque Nacional de Guerrero, Croat 67442 (MO). Morelos: Cuernavaca, Bourgeau 1420 (K, P); 1350 m, Quarles van Ufford 95 (U); 5000 ft., Pringle 8093 (BH, BM, BR, CM, F, G, GH, H, HBG, ISC, K, LL, MASS, MEXU, MO, NY, P, POM, RSA, UC, US); Rose & Hough 4439 (US); Río Pollo, below Salto San Antonio, Fraccionamiento San Antonio, W of Colonia Carolina, NW of Center of Cuernavaca, 1500 m, 18E57'N, 99E15'W, Croat & Hannon 65778 (B, CM, F, GH, K, MEXU, MO, NY, US); Matuda 26030 (MEXU); 25982 (F, MEXU); Moore & Bunting 8820 (BH); Barranca Santa Clara, N de Acatlipa, 1450--1550 m, Vázquez 3094 (MEXU). Veracruz: Córdoba-Veracruz, Ejido San José de Gracia, below Peñuelo, ca. 730? m, Moore & Bunting 8873 (BH, MO).