Small shrub, 1-2.5 m tall, sparingly branched. Stem striate or canaliculate, glabrous. Prophyll 2-4 cm long, glabrous, caducous. Petiole 0.7-1.3 cm long, glabrous, deeply vaginate at base; blade thick chartaceous, not scabrous, not conspicuously glandular-dotted, oblong or elliptic-oblong, 13-16.5 x (3.5-)4-6.5 cm, apex abruptly long-acuminate, base equal or almost equally attached to petiole, acute, glabrous; pinnately veined, secondary veins 8-12 per side, prominent on both sides, anastomosing well within margin, originating from throughout primary vein, tertiary veins widely, distinctly reticulate. Inflorescence erect, white, becoming green; peduncle 1 cm long, minutely pubescent; spike 0.5-1 x 0.1-0.2 cm long, in fruit 2.5-4.5 x 0.3-0.45 cm, not apiculate; floral bracts saccate or galeate, glabrous, densely fimbriate; flowers densely congested; anthers reniform. Fruits 4-sulcate, globose, 3-4.5 mm in diam., truncate at apex, glabrous, stigmas 4, globose, sessile; seeds deeply 4-sulcate.
Several collections recorded from French Guiana representing Piper aulacospermum had been assigned to P. piscatorum. Comparing the type of the latter and collections used to describe P. aulacospermum it became obvious that the French Guianan collections belong to P. aulacospermum. Differentiating characters are: in P. aulacospermum the secondary veins prominent above, tertiary venation distinctly reticulate (instead of impressed or slightly prominulous in P. piscatorum); peduncle 1 cm long, slightly pubescent (instead of 0.4-0.5(-1) cm long, glabrous in P. piscatorum); the fruits are 4-sulcate (caused by the shape of the seeds), 3-4.5 mm in diam. (instead of smooth, ca. 1.5 mm in diam. in P. piscatorum).