Philodendron ‘Sucre's Slim’
It appears this plant originated in Brazil, or possibly Panama.
Distributed by Dimitri Sucre in Rio in 1989. He called it "Sucre's Slim".
The petiole is terete near the apex (top) but there are are striations on the flattened adaxial surface near the base, the blades have not grown larger than 8 inches and the petioles are around double the length of the blade. The widest point on the blade is barely 1 inch. The young blades emerge from a petiolar sheath but there are also cataphylls visible in the photos. The plant appears to grow as a clumping form.
Unless this is simply a very slow grower this one may also qualify as one of the smallest Philodendron species known.