Isachne pallens is a perennial grass species that typically reaches a height of 30-60 cm. The culms of this grass are lax, decumbent, and geniculate below, with a tendency to root at the nodes. The stems are glabrous. The leaves are simple and alternate, with linear lanceolate blades approximately 6 cm long and 2-3 mm wide. These blades are pale green and mostly glabrous, except for a scaberulous texture at the base. The margins of the leaves are thin and entire, and the veins run parallel. The sheaths are short-pubescent at the collar, and the ligule is ciliate, enhancing the fine detailing of the plant. The flowers occur in an ovoid panicle, ranging from 3-8 cm long to 2-3 mm wide. The panicle branches are slender and filiform, with longer pedicels than the spikelets. The spikelets are ellipsoid to obovoid and measure approximately 2 mm long. The glumes are ovate and slightly longer than the florets, with the first glume indistinctly 5-nerved and the second glume 7-nerved. The first fertile floret is perfect and ellipsoid, characterized by crisped villous hairs. Lemmas are plano-convex or hemispherical, 1.3-1.6 mm long, evenly long-pilose, with margins that slightly clasp the palea. The palea is oblong to elliptic, 1.3-1.5 mm long, and is glabrous except for arachnoid pubescence at the base. The fruit is a pale brown caryopsis, ovoid to plano-convex or lenticular, and roughly 1 mm long. It is found in mesic forests, often on rocks exposed to waterfall spray, along streams, or in wet forests between 240-760 meters.