Appressed-climbing liana; internodes 1-4 cm long, most longer than broad, 1.3-2.5 cm diam., (drying less than 1 cm diam.), dark green, turning grayish brown drying dark yellow-brown, narrowly grooved longitudinally; cataphylls sharply 2-low-ribbed, 17 cm long, deciduous; LEAVES: petioles 16.5-25 cm long, matte, dark green (geniculum paler), drying dark brown, 5 mm diam.; blades ovate to narrowly ovate, 20-29.5 cm long, 13-17.5 cm wide, (1.3)1.6-1.8 times longer than wide, abruptly acuminate at apex, subcordate at base, bicolorous, dark green and semi-glossy above, moderately paler and semi-glossy below, drying yellowish gray-green and matte above, with minute, pale, linear cellular inclusions, slightly paler green below, drying yellow-brown and weakly glossy, with mostly short, sometimes weakly elongated, dark cellular inclusions; sinus arcuate, 1.5-2 cm deep; midrib sunken and purplish-spotted above, narrowly raised below; primary lateral veins 4-5 pairs, arising at 45-70°, purple tinged, drying ± concolorous below; posterior lobes 4-6 cm long, broadly rounded; basal veins 2-3 pairs, 1st free to the base, 2nd & 3rd weakly fused ca. 1 cm; posterior rib not naked along the sinus. INFLORESCENCES 3 per axil; peduncle 2.5-2.8 cm long, 2-3 mm diam., drying reddish brown; spathe 5-7.5 cm long, yellow-green, drying 6-8 mm diam., 3 cm wide when flattened, drying light yellowish brown; spadix 5.7-7 cm long; pistil 3 cm long, 6-7 mm diam., slightly narrower at base and apex, yellowish; staminate portion 3-4 cm long, narrowly tapered to apex, whitish, becoming purplish post-anthesis.
Characterized by its narrowly ovate, subcordate blades that dry yellow-brown on the lower surface, and especially by its clusters of up to 3 small, greenish inflorescences.
Philodendron moonenii appears to be endemic to French Guiana and known only from the type locality.