A small, slender, collybioid yellow cortinarius, originally described from New Zealand and now placed in Aureonarius following the modern Cortinariaceae revision. It is characterised by its pale yellow to yellow-ochre cap, slender stipe, rust-brown spores, and a delicate cortina that may be inconspicuous in dry weather. This species is one of the least robust and most “collybia-like” members of Aureonarius, hence the epithet collybianus.

Cap: 10–25 mm diam., convex to plano‑convex, sometimes shallowly depressed with age; surface dry, smooth to faintly fibrillose; colour pale yellow to yellow‑ochre, sometimes slightly darker at the disc. Margin often paler and may show faint veil fibrils in young specimens.
Lamellae: adnate to adnexed, moderately crowded; initially pale yellow‑ochre, becoming rust‑brown as spores mature; edges even.
Stipe: 25–60 × 2–4 mm, slender, cylindrical, sometimes slightly broadened at the base; surface pale yellow to whitish‑yellow, often with very fine rusty cortina fibrils near the apex, though these may be sparse or absent in dry conditions. Flesh pale yellowish, unchanging.
Veil: a delicate cortina, often sparse and easily overlooked; becomes rust‑brown when spores adhere.
Odour/taste: indistinct.