Philodendron arcuatum K. Krause, Pflanzenr. IV 23Db(Heft 60): 72. (1913). Type: Bolivia. Pando Río Acre, at Cobija (on Brazilian border, SW of Río Branco), 11º02'S, 68º44'W, Ule 8819 (holotype, B). Philodendron holmquistii G.S. Bunting, Acta Bot. Venez. 10: 297. (1975). Philodendron brevispathum Schott subsp. Holmquisti, (G.S. Bunting) G.S. Bunting, Phytologia 64(6): 466–467. (1988). - Type: Venezuela. Amazonas: Pueblo Viejo, open zone between the Río Pacimoni and the forest, 100 m, 1º50'N, 66º30'W, Steyermark & Bunting 102495 (holotype, VEN; isotype, MY).

Terrestrial or hemiepiphytic. Stem scandent, coarsely scabrous, densely covered with trichome-like, often branched scales; internodes elongate, 7.5–14(23) cm long, 8–15 mm diam., longer than broad, epidermis reddish brown, loosening and flaking, without fissures; roots drying tan to dark brown, few per node. Cataphylls 6–9 cm long, soft, unribbed, green, drying dark reddish brown, eventually deciduous. Petioles 10–43 cm long, 3–7 mm diam., subterete to bluntly C-shaped, somewhat spongy. Blades ovate to ovate-triangular, concolorous, semiglossy, thin, acuminate at apex, cordate at base, 16–36 cm long, 11–26 cm wide (1.4–2 times longer than wide), (0.8–1.6 times longer than petiole), broadest at or above middle, upper surface semiglossy, lower surface semiglossy; anterior lobe 12–30 cm long, 10.8–24 cm wide (1.3–2.4 times longer than posterior lobes); posterior lobes somewhat triangular to narrowly triangular to rounded, or rounded to with hastate or flaring lobes, 5–15 cm long, 4.9–11.5 cm wide, subacute; sinus narrow or sometimes V-shaped, 9–11 cm deep. Midrib sunken above, convex to raised, drying slightly paler below; basal veins 3–4 per side, with 1 free to base, coalesced 4–10 mm, or with 2–3 veins colaesced to 3 or 4 cm; posterior rib not naked or obscurely and briefly naked to 0.5 cm long; primary lateral veins (3)4–5 per side, departing midrib at a 55–70 degree angle, gradually ascending to the margins, weakly sunken above, convex and drying slightly darker below; interprimary veins almost as conspicuous as primary lateral veins; minor veins arising from both the midrib and primary lateral veins; tertiary veins visible and darker than surface below. Inflorescences erect, 1 per axil; peduncle 1–7 cm long, 2.5–5 mm diam., subterete. Spathe 6–10.5 cm long, (1.4–4.6(9) times longer than peduncle); spathe blade green outside, red inside; spathe tube green to greenish white outside, 4–4.5 cm long, 2–2.5 cm diam., green to white inside. Spadix sessile; 7–9.5 cm long, whitish to yellowish; pistillate portion 2–3 cm long, 3.5 cm diam. throughout; staminate portion 5–7 cm long; fertile staminate portion 5–10 mm diam.; sterile staminate portion 5–6 mm diam.; ovary ca. 6-locular, with axile placentation; ovules 6–14 per locule, 0.3–0.4 mm long, longer than funicle; funicle 0.2 mm long, adnate to lower part of partition, style similar to style type B; stylar canals emerging at base of pronounced apical depressions; style apex drying dark brown with a pale undulate margin and a central solitary stigmatic pad; the androecium truncate, prismatic, margins distinctly scalloped, irregularly 4–5-sided, 0.9 mm long; thecae oblong, 0.4 mm wide, nearly contiguous. Infructescence with peduncle 4 cm long, spathe 5–6 cm long; spadix, 3.5–4 cm long, 2.5 cm wide; berries pale yellow, 6 mm long, 3 mm diam.; seeds 4–6 per berry, oblong to weakly ovoid, 1.4 mm long, 0.4–0.5 mm diam.

Type: Panama. Canal Zone: Chagres River, Fendler 431 (holotype, MO; isotype, K). Philodendron arcuatum K. Krause, Pflanzenr. IV 23Db(Heft 60): 72. (1913). Type: Bolivia. Pando Río Acre, at Cobija (on Brazilian border, SW of Río Branco), 11º02'S, 68º44'W, Ule 8819 (holotype, B). Philodendron holmquistii G.S. Bunting, Acta Bot. Venez. 10: 297. (1975). Philodendron brevispathum Schott subsp. Holmquisti, (G.S. Bunting) G.S. Bunting, Phytologia 64(6): 466-﷓467. (1988). - Type: Venezuela. Amazonas: Pueblo Viejo, open zone between the Río Pacimoni and the forest, 100 m, 1º50'N, 66º30'W, Steyermark & Bunting 102495 (holotype, VEN; isotype, MY).

Napo: 230 m, 0°08N 76°24W, 27 Apr 1984, Croat 58586 (MO). - Costa Rica, Nicaragua, and Panama. Additional specimens examined. COSTA RICA. Heredia: Puerto Viejo﷓Guápiles, along Río Puerto Viejo, 7 km N of Buenos Aires, 10º23'30"N, 83º48'30"W, Croat 68401 (K, MO); La Selva Field Station, Grayum 2300 (DUKE, MO); Grayum 2642 (DUKE, F, MO), 100 m, Hammel & Trainer 10810 (DUKE); Río Frío de Sarapiquí, between Río Sucio and railroad tracks, SW of Finca Zona Ocho, 110 m, 10º18'N, 83º52'30"W, Grayum & Hammel 5568 (MO). Limón: Río Bananito-Cahuita, near Punta Vargas ca. 4 km S of Cahuita, 0-﷓10 m, Burger et al. 10493 (F, MO); 16 airline km SW of Barra del Colorado, 10-﷓120 m, 10º39'N, 83º40'40"W, Davidse & Herrera 31254 (MO); Refugio Barra del Colorado, area between Río Chirripocito and Río Sardina, 12 m, 10º38'N, 83º45'W, Grayum et al. 9742 (AAU, CR, MO); Finca Tapezco﷓-La Suerte, 29 air km W of Tortuguero, 40 m, 10º30'N, 83º47'W, Davidson & Donahue 8842 (MO); 40 m, 10º30'N, 83º47'W, 8970 (RSA, MO); Gandoca-﷓Manzanillo, Gandoca (slightly to N of trail from Mata de Limón), 0-﷓5 m, 9º36'N, 82º36'30"W, Grayum et al. 8024 (CR, K, M, MO); Cerro Coronel, 10--40 m, 10º40'N, 83º40'W, Stevens et al. 24670 (CR, MO); Parque Tortuguero National Park, Tortuguero, 2 m, Robles 1410 (CR, MO); 4 m, 10º32'N, 83º30'W, 1877 (CR, F, MO); near Boca de las Lagunas de Tortuguero, 0﷓-30 m, 10º34'N, 83º32'W, Burger & Antonio 11236 (F, MO, U). NICARAGUA. Matagalpa: Ranchería, 11 km al NE de Muy Muy, 280 m, 12º46'N, 85º31'W, Moreno 24433 (MO). Río San Juan: Quebrada Santa Crucita, 50 m, 11º02'N, 84º25'W, Moreno 23445 (MO); Sábalo, 1 km N of Río San Juan, 100 m, 11º02'N, 84º27'W, 26111 (MO); Boca de Sábalos, cerca de "La Toboba", 70-﷓90 m, 11º03﷓-04'N, 84º28﷓-29'W, Robleto 1833 (MO, US). Rivas: Isla de Ometepe, La Argentina, 300﷓-800 m, 11º27'N, 85º32'W, Moreno 22112 (CM, MO). Zelaya: La Barra de Punta Gorda, 0-﷓2 m, 11º30'N, 83º47'W, Moreno & Sandino 13298 (MO); Caño Monte Cristo, "La Grupera", 10 m, 11º33'N, 87º48'W, Moreno & Sandino 14739 (MO); Puerto Cabezas-﷓Río Wawa, Ibo Tingní, drainage of Caño Sung Sung, 10 m, 14º9-﷓11'N, 83º29﷓-31'W, Stevens 10636 (ENCB, MO); Santa Marta, 5 m, 14º18'N, 83º37'W, Stevens & Moreno 19623 (MO); SW of Bluefields, 10﷓-40 m, 11º59'N, 83º46'W, Stevens 19736 (CAS, L, MO, UWL). PANAMA. Colón: Miguel de la Borda, Croat 10012 (MO, SCZ). San Blas: Playón Chico, road to Isisukun, 0-﷓10 m, 9º20'N, 78º13'W, Herrera 596 (MO).