Creeping to scandent herb, rheophytic. Internodes green, 1-18 x 0.4-1 cm. Petioles 6-20 x 0.3-0.5 cm, sheath convolute to expanded, liguliform apex, nonsheathed portion of petiole 0.5-4.5 x 0.2-0.3 cm. Leaf blade entire, elliptic to oblanceolate, slightly oblique, 8.5-29 x 4-7.5 cm, subcoriaceous, dark green adaxially, paler abaxially, base acute to cuneate, rarely obtuse, apex long acuminate, rostrate; secondary nerves 4-6, poorly prominent, arising at an angle of 25-45°. Inflorescence solitary, peduncle 1-3 x 0.4-0.7 cm, spathe yellowish-green out-side, cream-colored internally, 9-16.5 cm long, 2-4 cm diam., acuminate; spadix 4.5-7.6 cm long, obliquely stipitate, stipe 1-2 cm at its longer side, fertile male portion terete, rounded at apex, 2.5-4.5 x 0.5-1 cm; sterile male portion 0.5 x 0.6-1 cm; female portion green, 1.6-2.5 x 1 cm. Female flowers 2-3-androus, stamens prismatic ca. 1 x 1 mm, staminodes prismatic to obpyramidal, ca. 2 x 1 mm, gynoecium subprismatic 2-3 x 1 mm, ovary 2-3-locular, locules 20-24-ovuled, funicles 2-3 x longer than the ovules. Berries cream-colored to greenish, 6-10 x 2-3 mm. Seeds long-elliptic, ca. 1 x 0.3 mm.
Creeping or scandent herb. Stem terete, slightly striate, internodes dark green, glossy, 1 - 18 x 0.4 - 1 cm; adventitious roots brown, c. 0.2 cm diam. LEAVES: Petiole green, 6-20 cm long; sheath partially closed, with left and right sides of unequal width, 1 - 5 mm wide, the base surrounding the stem, apex ligulate, acute to rotund, projecting for 1 - 7 mm; the non-sheathing part of the petiole 0.5 - 4.5 cm long. Lamina almost always oblique, elliptic, narrow-elliptic, oblong or oblanceolate, straight to subfalcate, 8.5 - 29 x 4 - 7.5 cm, base acute to cuneate, apex long- acuminate; subcoriaceous, adaxially dark green, abaxially paler; primary lateral veins 4 - 6, slightly prominent abaxially, arising at an angle of 25º- 45º. INFLORESCENCE solitary, terminal. Peduncle green, 1 - 3 x 0.4 - 0.7 cm; spathe 9 - 16.5 x 2 - 4 cm, outside greenish-yellow, inside cream, tip long-acuminate; spadix 4.5 - 7.6 x 0.7 - 1.2 cm, stipe 1 - 2 cm long on the longer side, 0.5 - 1 cm on the shorter side, fertile male zone 2.5 - 4.5 x 0.6 - 1 cm, rounded at apex, intermediate sterile male zone 0.5 x 0.6 - 1 cm; female zone green at anthesis, 1.6 - 2.5 x 0.7 - 1.2 x cm; male flower prismatic, 2 - 3-androus, c. 0.1 x 0.1 cm; staminodes prismatic, c. 0.1 x 0.1 cm; gynoecium subprismatic, c. 0.3 x 0.1 cm; locules 2 - 3, ovules 20 - 24 per locule, axially disposed up to the middle of the axis, funicles three times longer than the ovules, with trichomes at the base. INFRUCTESCENCE: Fruit a berry, cream or greenish, prismatic, 0.6 - 1.0 x 0.2 - 0.3 cm, most of the seeds situated at the berry apex. Seeds elongate, c. 1.0 x 0.3 mm (Fig. 1).
Philodendron flumineum is one of the few (If not the only) rheophytic species of the genus and occurs only in Goias State (including the Federal District), always along medium to fast flowing rivers. In limestone outcrops, it occurs where permanent flowing water exists, growing appressed to the rocks.