Terrestrial or sometimes hemiepiphytic; internodes short, semiglossy, 2–7 x 2–6 cm, shorter than long, medium green with coarse white striations, drying dark tan or medium brown with longitudinally wrinkled slightly flaky epidermis; cataphylls to 13 cm, unribbed, gradually tapered at the apex, yellow-green, drying with dark brown pieces of epidermis over thin pale fibers, persisting intact but becoming mushy and dark brown. LEAVES erect to spreading; petioles 23–125 cm x 5–10 mm (dry), terete, obtusely flattened adaxially, spongy, medium green with coarse white striations, semiglossy, drying dark brown, often with a darker brownish black geniculum; blades ovate, moderately coriaceous, obtuse-acuminate at the apex, deeply cordate at base, 27–60 x 18.5–44 cm, 1.2–1.6x longer than wide, 0.5–0.8x as long as petiole; adaxial surface semiglossy, dark green, drying glossy and very dark olive-green to black; abaxial surface matte to weakly glossy, paler than adaxially, drying weakly glossy; anterior lobe 22–45.5 x 18.5–44 cm, 2–2.6x longer than posterior lobes; posterior lobes 8.5–21.5 x 9– 24.5 cm, rounded to rectangular; sinus spatulate to rhombic, 4–15 cm deep; midrib flat and paler than blade adaxially, narrow-rounded, matte, darker than blade abaxially; primary lateral veins 8 to 11 per side, spreading from midrib at 50º–60º angles, curving gradually toward apex, more abruptly so at margin, downturned at midrib, narrowly sunken and paler than blade adaxially, convex and darker than blade abaxially, drying dark brown; basal veins 5 to 7 per side, 2 to 3 veins free, 4 to 5 coalesced for 2–4 cm, not to barely naked, drying dark brown; interprimary veins obvious; secondary veins numerous, fine, drying with a stitched appearance; cross veins numerous, indistinct, minute. INFLORESCENCES erect; 1 to 5 per axil; peduncle 13–16 cm x 3–5 mm (dry), much shorter than petiole, medium green with coarse white striations, drying dark brown to black; spathe long-tapered, constricted above tube, semiglossy, 15– 18 cm, drying dark brown; spathe blade white on both surfaces; spathe tube pale green to medium yellow-green with white margins outside, white-speckled inside; spadix weakly exserted from the spathe at anthesis, 9–13 cm; pistillate portion greenish white, cylindrical, 3.8–5 cm x 9–11.5 mm; staminate portion 6–8.5 cm; fertile staminate portion white, ellipsoid, 4–6 cm x 7.5–11 mm at widest point, barely tapering at apex, narrower than pistillate portion; sterile staminate portion 1–2.5 cm x 9– 10.5 mm, narrower than pistillate and fertile staminate portion; pistils 2.2 mm; ovary 4- to 5-locular, ovules with axile placentation, about 20 per locule. INFRUCTESCENCE to 13 cm, pistillate portion 5–6.5 cm.
The species is a member of subgenus Philodendron, section Philodendron, subsection Philodendron, series Philodendron and is characterized by its terrestrial habit; the coarse white striations found on the internodes, petioles, peduncles, and inside the spathe (hence its epithet); unribbed cataphylls that weather to thin fibers; and greenish black–drying cordate blades with few primary lateral veins and a matte abaxial leaf blade surface. Also characteristic are the inflorescences with white spathe blades outside and inside, and spathe tubes yellow-green outside and white within.
A species that can be mistaken for Philodendron striatum is P. venulosum Croat & D. C. Bay. These two species can both occur as terrestrials and have similarly shaped blades. The latter species differs by more often growing as a hemiepiphyte, its 2-ribbed cataphylls that persist as thick coarse fibers with reddish brown bases, its leaf blades that are semiglossy below drying dark reddish green, and its bluntly rounded inflorescences with pale green blades and rose-colored tubes.