Planta hemiepiphytica; internodia 2.5--10 cm longa, 2--5 cm diam., cano-viridia, in sicco flavibrunnea; cataphylla mollia, 16--29 cm longa, leniter vel acute 2-costata, persistenta semi-intacta; petiolus subteres, 37--74 cm longus, 1.5--2 cm diam.; lamina ovato-cordata, 41--46 cm longa, 19--37.5 cm lata, in sicco atribrunnea; costa postica haud nuda aut usque 2.5 cm; inflorescentia 2; pedunculus 8--9 cm longus; spatha 14--14.5 cm longa, omnino viridis; pistilla 5--6-locularia; loculi 1-ovulati.

Hemiepiphytic; internodes coarsely white-striate beneath each node, somewhat soft, drying semiglossy, 2.5--10 cm long, 2--5 cm diam., gray-green, drying yellow-brown, epidermis fissured closely; roots moderately few per node, to ca. 30 cm long, drying 2--3 mm diam., reddish brown, semiglossy, sharply ridged; cataphylls soft, 16--29 cm long, weakly to sharply 2-ribbed, green to pale red, drying thin, brown, persisting semi-intact at upper nodes; petioles 37--74 cm long, (averaging 51 cm long), 1.5--2 cm diam., subterete, weakly spongy, medium green, weakly flattened near apex adaxially, surface light green streaked; blades ovate-cordate, acuminate at apex, prominently lobed at base, 41--46 cm long, 19--37.5 cm wide (1.1--1.7 times longer than wide), upper surface dark green, semiglossy to weakly glossy, drying dark brown, lower surface semiglossy, much paler, drying yellow-brown; posterior lobes rounded, 12.5--15 cm long, about as broad as long; sinus hippocrepiform, 8--11 cm deep; midrib flat to raised, paler than surface above; basal veins 5--6 per side, with the uppermost free to base, second basal vein coalesced no more than 1 cm, (2)3--4 coalesced 2.5--5 cm; posterior rib not at all naked or naked up to 2.5 cm; primary lateral veins 4--6 per side, raised or sunken, darker than surface, drying dark brown below; interprimary veins in part sunken, the remainder flat but visible below; minor veins alternately strongly or weakly visible, with the more prominent veins weakly stitched below, arising from both the midrib and primary lateral veins. INFLORESCENCES 2 per axil; peduncle 8--9 cm long, 1--1.5 cm diam., fleshy, drying dark brown; spathe 14--14.5 cm long, weakly constricted above the tube, green throughout, narrowly acuminate at apex, drying dark brown outside; spathe tube 5.5--6.5 cm long, 2--2.3 cm diam.; spadix sessile; to 11.7 cm long; pistillate portion cylindrical, broadest midway, 1.2--1.3 cm diam., weakly tapered in both directions; staminate portion 8.5--9 cm long; fertile staminate spadix broadest at sterile portion, constricted to 9--10 mm ca. 1.5 cm above base, then clavate upward, bluntly tapered at apex, 10--11 mm diam. in upper one-third, 7--8 mm diam. 1 cm from apex; sterile staminate portion 12--13 mm diam.; pistils 1.6 mm long; ovary 5--6-locular, 0.9 mm diam., with sub-basal placentation; ovules 1 per locule, contained within transparent, gelatinous matrix (no true envelope), 0.3--0.4 mm long, longer than funicle; funicle 0.2--0.3 mm long, with a tuft of trichomes near base, style 0.7 mm diam., similar to style type B; style apex flat to concave; the androecium truncate, more or less prismatic, margins mostly irregularly 5-sided, 0.7--1.1 mm long; thecae oblong, 0.4 mm wide, more or less parallel to one another, contiguous. PREADULT leaves with petioles 17--20 cm long; blades to 31 cm long and 15 cm wide.

Flowering phenology of Philodendron dominicalense is unclear owing to its rarity, but since it was found in flower in May, during the early wet season, it probably both flowers and fruits in the wet season.

Philodendron dominicalense is endemic to southwest Costa Rica on the Pacific slope in the vicinity of the type locality along San Isidro-Dominical road, at ca. 1000 m, in Premontane rain forest.

Philodendron dominicalense is a member of P. sect. Calostigma subsect. Glossophyllum ser. Ovata. This species is distinguished by its appressed epiphytic habit, thick grayish green stems with internodes mostly longer than broad, soft, weakly 2-ribbed, semi-persistent, intact cataphylls, subterete petioles about as long as the blades, ovate-cordate brown-drying blades with the posterior ribs naked for a short distance to the sinus, and paired short-pedunculate inflorescences with green outer spathe surfaces and one ovule per locule.

Philodendron dominicalense is vegetatively almost identical to P. dodsonii, but that species differs in having the spathe red-purple to dark reddish outside and ovaries with axile placentation and about 20 ovules per locule (versus spathe tube green outside, ovaries with basal to sub-basal placentation, and 1 ovule per locule). Philodendron dodsonii also differs in usually having persistent fibrous cataphylls, a sunken upper midrib (versus flat to raised) and posterior ribs usually prominently naked for 6 cm (versus not at all naked or naked to only 2.5 cm).

This species is also similar to P. schottianum, especially in shape and color of the dried blades. The latter species differs in having shorter internodes with thicker cataphylls which dry yellow and weather promptly into a coarse network of fibers (versus persisting semi-intact at upper nodes then deciduous).

Additional specimen examined.

COSTA RICA. San José: San Isidro del General--Dominical, SW of San Isidro, 6 mi. from Río Pacuare, 1000 m, Croat 35454 (MO).