Rhynchospora caduca is a perennial plant with short–creeping rhizomes. The culms are loose to moderately densely tufted, standing 60–120 cm tall and 1.8–3 mm in diameter near the base. The stems are trigonous, smooth, and 3–4–nodose below the inflorescence. The leaves are simple and primarily basal, with a few cauline and well-spaced leaves. The blades are herbaceous, linear, and shorter than the culm, measuring 3–6 mm wide. The leaf margins are entire. The leaves are sheathing, with sheaths measuring 2–5 cm long. The cauline sheaths are green, while the basal ones are reddish-brown or yellowish-brown. Stipules are absent. The flowers are arranged in inflorescences composed of 4–5 well-spaced, anthelate partial panicles, which are decompounded and 2–7 cm long and 1.5–3 cm wide. These panicles are moderately dense, with exserted peduncles. The branches are numerous, 1–3 cm long, and further branched, each bearing 3–5 spikelets. The lowest two leaf-like bracts are longer than the subtending partial panicle, and the upper bracts are as long as or shorter than the subtending panicle. The spikelets are brown, solitary, or in clusters of 2–3, subsessile, and ovate, measuring 3.5–4.5 mm long and approximately 2 mm wide. The glumes, numbering 6–8, are brown to rusty brown, ovate to broadly ovate, and acute, with membranous margins. The midnerve is slender and prolonged into a straight mucro or short awn. The flower-bearing glumes are 2.8–3.7 mm long and 2–3 mm wide. The flowers are all bisexual (perfect), although sometimes the distalmost flowers are staminate. The perianth consists of 6 bristles, longer than the achene. The corolla (petals) is absent. The ovary is superior, with a deltoid base, 0.6–0.8 mm high and wide, and ciliate. The achenes (pictured) are broadly obovate and lenticular, measuring 1–1.6 mm long and 1–1.4 mm wide. The surface is transversely undulate–rugose and cancellate with longitudinally oblong cells. Each fruit contains one seed with a thin seed coat free from the pericarp. The embryo is basal, and the endosperm is abundant. It is naturalized in wet, disturbed areas between 320–1,400 meters.