Rhynchospora rugosa subsp. lavarum is a perennial sedge that lacks conspicuous rhizomes and typically forms dense tufts. Culms (stems) are slender, erect, and 20–70 cm tall, with a width of 0.5–0.8 mm, and are 1- to 2-noded just below the inflorescence. It produces few leaves, mostly basal, with 1–2 cauline leaves. The leaf blades are linear, measuring 8–30 cm in length and 0.8–2.5 mm in width, with entire margins and parallel venation. Leaf sheaths are up to 4 cm long and green, while the basal sheaths are pale brown. Stipules are absent. The inflorescences consist of 2–5 small, widely spaced, anthelate partial panicles on the upper two-thirds of the culm. Each panicle is solitary at a node, open, and corymbiform, bearing 3–5 filiform branches with clusters of 2–6 subsessile spikelets. These inflorescences are 0.8–3 cm long, with linear to setaceous bracts. The lower 1–2 bracts exceed the length of the inflorescence and are sheathing at the base. Spikelets are ovoid–ellipsoid, subterete, and 4–5 mm long by about 2 mm wide, reddish to brown in color. Each spikelet contains 6–8 glumes, of which the middle 3–4 bear flowers. These glumes are membranous, ovate, and terminate in a short recurved awn. Flower-bearing glumes measure 3–3.5 mm in length and approximately 2 mm in width. Each flower is bisexual (perfect), though the terminal flower may be staminate. There are 6 perianth bristles per flower, 2.5–2.7 mm long, antrorsely spinulose, and extending beyond the achene, which includes the persistent style base. Petals are absent. The ovary is superior, with a deltoid style base 0.5–0.6 mm long and approximately 0.5 mm wide, tapering gradually into a slender style. The fruits are reddish brown achenes, obovate to obovate–elliptic in shape, approximately 1.5 mm long and approximately 0.8 mm wide, with faint transverse rugulosity. Each achene contains a single seed, with a thin seed coat that is free from the pericarp. The embryo is basal, and the endosperm is abundant. It occurs in wet forests and bogs, as well as in mesic forest habitats, between 280-1,620 meters.