Planta epiphytica; caulis scandens; internodia 5--6.5 cm longa, 4--5 mm diam.; cataphylla leniter vel acute 2-costata, decidua; petiolus 9--11 cm longus, usque 4 mm diam., anguste et obtuse sulcatus; lamina ovata, leniter subcordata, 9.8--11 cm longa, 7--8 cm lata, in sicco flavibrunnea; nervis lateralibus I absentibus; inflorescentia 1; pedunculus 4.7 cm longus, 3.5 mm latus; spatha omnino in superficebus ambabus maronnina, 9--9.3 cm longa; pistilla 5-locularia; loculi 2-ovulati.

Epiphytic; stem scandent; leaf scars inconspicuous; internodes terete, 5--6.5 cm long, 4--5 mm diam., much longer than broad, drying yellowish brown, epidermis fissured narrowly; roots dark brown, drying moderately fuzzy, slender, 1 mm diam., very few per node; cataphylls weakly to sharply 2-ribbed, glossy, deciduous; petioles 9--11 cm long, to 4 mm diam., narrowly and obtusely sulcate adaxially, surface minutely wrinkled; sheath conspicuous, the tip free-ending (2--3 mm long); blades ovate, acuminate at apex (acumen inrolled, 1--2 mm long), weakly subcordate at base, 9.8--11 cm long, 7--8 cm wide (1--1.4 times longer than wide; about equal in length to petiole), broadest in lower one-third, margins revolute, drying reddish brown, upper surface medium green, drying grayish green, semiglossy, lower surface weakly glossy, moderately paler, drying yellowish green; anterior lobe 9--10.5 cm long, 7--8 cm wide (5.9--7.1 times longer than posterior lobes), broadest in lower one-third; posterior lobes 2--2.4 cm long, 2.8 cm wide, rounded; sinus obtusely angular, 5 mm deep; posterior rib lacking; midrib concave above, moderately raised, drying paler than surface below; basal veins numerous on each side but none of them outstanding, primary lateral veins lacking or indistinguishable from minor veins; minor veins close, arising from the midrib only, arising from both the midrib and primary lateral veins. INFLORESCENCES 1 per axil; peduncle 4.7 cm long, 3.5 mm diam., dark brown; spathe erect, subcoriaceous, 9--9.3 cm long, (2.1 times longer than peduncle), maroon throughout on both surfaces; spathe blade 6.9 cm long; spathe tube 4.5 cm long, spadix green throughout (probably juvenile), narrowly rounded at apex, 7.3 cm long, constricted below sterile staminate portion; pistillate portion drying grayish, slightly tapered toward the apex, 2.1--2.5 cm long in front, 1.2 cm long in back, 4.5--5 mm diam. at apex, 5--6.8 mm diam. at middle; staminate portion 4.5--6.1 cm long; fertile staminate portion white, gradually tapered towards apex, 6.5--6.8 mm diam.; pistils 1.1 mm long; ovary 5-locular, 0.9 mm diam., ovule sac ca. 0.5 mm long, with sub-basal placentation; ovules 2 per locule, contained within transparent ovule sac, ca. 0.2--0.3 mm long, longer than funicle; funicle 0.1--0.2 mm long (can be pulled free to base), style 0.7--0.9 mm diam., similar to style type D; style apex rounded; style boss broadly and gently rounded; stigma button-like, distinctly lobed, 1 mm diam., 0.3 mm high, covering entire style apex, inserted on style boss; the androecium truncate, prismatic, margins irregularly 4--6-sided, 0.9--1.1 mm long, 3--5 mm diam. at apex; thecae oblong to weakly ellipical, 0.4 mm wide, more or less parallel to one another; sterile staminate flowers subrounded, 5--9 mm wide, grayish to pale orange.

Flowering in Philodendron brewsterense is based on a single flowering collection made in April in an area that is somewhat aseasonal.

Philodendron brewsterense is endemic to Panama, where it is known only from the type specimen collected on Cerro Brewster in Comarca de San Blas Province, at 850 m elevation in a Premontane rain forest life zone.

Philodendron brewsterense is a member of P. sect. Calostigma subsect. Glossophyllum ser. Glossophyllum. The species is recognized by its scandent habit with internodes much longer than broad, drying yellowish brown and narrowly fissured, small, (<8 cm diam., <11 cm long) coriaceous, ovate, yellowish brown blades lacking primary lateral veins, and solitary inflorescence with the outer surface surface maroon.

Philodendron brewsterense is apparently unrelated to any other species but is most similar to P. crassispathum and resembles juvenile plants of that species. The latter differs, however, in having juvenile leaves with an arcuate sinus and adult leaf blades usually more than 20 cm long and with four to six pairs of primary lateral veins.