Epiphyte, stems slender, elongate; internodes longer than broad, 7-10 mm diam., drying medium brown, smooth, matte, finely ribbed upon magnification; cataphylls weakly 2-ribbed, 7.3-10.4 cm long, drying red dish brown, remaining mostly intact, weathering partially to fibres near the base, finally deciduous. Leaves with petiole 12.3-20.5 cm long (averaging 16 cm), dry ing 2-3 mm in diam., sharply and broadly sulcate, drying darker than the blades, sheathed to about 2 cm at base but to 10-12 cm when subtending an inflorescence; blade 19.6-27.3 cm long, 5.3-9.9 cm wide, (averaging 23 7.9 cm) 2.9 longer than wide, 1.4 longer than the petiole, narrowly ovate to ovate-elliptic, asymmetrical with one side 0.9-1.3 cm wider, acuminate at apex, inequilateral and rounded to weakly subcordate at base, sometimes weakly decurrent onto petioles, dark green and matte above and lighter green underneath, drying yellowish to yellow; upper surface drying minutely granular upon magnification with a sparse array of short, pale, linear cellular inclusions; lower surface drying weakly glossy to matte with a dense array of somewhat darkened speckles; midrib flattened upon drying, some what raised on the upper surface, drying lighter than the blade on the lower surface; primary lateral veins 3-4 per side, arising at a 50 to 60o angle, curving upwards as they reach the margin; minor veins fine, close, moderate ly visible and weakly raised upon drying. Inflorescence with spathe 6.5-10.7 cm long, moderately constricted above the tube, tube 4.5 cm long, red on outside, blade white; spadix white; pistillate portion (post-anthesis) 3 cm long, 2.7 cm diam.; staminate portion 4.5 cm long, 1 cm diam.; sterile staminate portion c. 5 cm long, 1 cm wide; pistils 6.5-7.5 mm long, 3.2-3.6 mm diam., 5-6-locular, placentation axile, style weakly sunken at each division of the locules, stigma somewhat sunken, button-shaped, 1-1.2 mm diam., with 5-7 equidistant pits around its circumference; ovules 25-40 per locule, 1.3 mm long, the funicle 0.2 mm long.
Planta epiphytica; cataphylla 7.3-10.4 cm longa, semi intacta; folia petiolo 12.3-20.5 cm longo, lamina an guste ovata ad ovato-elliptica, 19.6-27.3 cm longa, 5.3 9.9 cm lata, nervis primariis lateralibus 3-4 utroque; spatha 6.5-10.7 cm longa, lamina alba et tubo rubro; ovula 25-40 in quoque loculo.
Philodendron grenandii is endemic to French Guiana, known only from the eastern part of the country at an elevation of 300-450 m in a Tropical moist forest or Premontane wet forest life zone. P. grenandii is known from only two collections, one made near the Brazilian border at Trois Sauts and the other at Huat Oyapock on Mt St. Marcel at 350-400 m.