Ischaemum byrone is a stoloniferous perennial grass typically growing from 40 to 80 cm tall. The culms of this species are erect, originating from a decumbent base, and are glabrous, though the nodes are sparsely covered with long hairs. The leaves are simple and alternate, with 7-20 cm long flat blades and 3-5 mm wide. These blades are glabrous, and the uppermost leaves are much reduced. The sheaths are also glabrous or occasionally long-pilose near the base with hairs up to 7 mm long. The uppermost sheaths tend to be inflated. The auricles are firm, measuring 3-4 mm long, and the ligule is prominent, membranous, ovate to truncate, and 1.5-3 mm long. The flowers feature racemes that are yellow to yellowish-brown. There are typically 2 or 3 racemes per inflorescence, often partially enclosed within the inflated sheath. These racemes are digitate and measure 4-10 cm long. The rachis joints are triangular and pilose at the base and along the margins toward the apex. The sessile spikelets are 6-7 mm long (excluding awns), and the first glume is oblong and pilose on the back with hairs up to 4 mm long. The second glume tapers into a scabrous awn 5-7 mm long. The pedicellate spikelets are 5-6 mm long, with a distinctly nerved first glume that is sparsely pilose and an awned second glume. The fruit is a golden, ovate caryopsis about 3 mm long. It is found among rocks near the ocean and occasionally inland, at elevations ranging from 0-75 meters.