Argyroxiphium caliginis is an upright (erect) or subspherical rosette shrub growing between 0.1–0.45 meters tall. Its leaves are silver or gray, sometimes brownish when dry, and typically narrowly sword-shaped, broadest below the middle. They are shallowly triangular in cross-section, measuring 3.5–15(–20) cm long and 0.2–0.5 cm wide at the middle. The leaves have obscure veins and are covered in a silky-floccose texture. The flowers are arranged in 15–50 heads in lax, racemose inflorescences that range from 10–40 cm in length and 5–12 cm in width. The receptacle is conical, about 2–4 mm in diameter, with a false involucral cup consisting of 12–20 receptacular bracts measuring 7–10 mm long. Each head typically contains 4–12 purplish ray florets 2–3-lobed, either weakly or not at all exserted. The rays are narrowly tubular at the base, with a limb approximately 2 mm long. There are around 30–110 disk florets per head, with purplish corollas measuring 3–4.5 mm in length. The basal portion of the corolla tube is sparsely to densely atomiferous glandular and occasionally sparsely pilosulous. The ray florets have a reduced pappus in the form of a minute coroniform rim, while the disk achenes possess a pappus of 6–8 scales up to 3 mm long on the dorsal summits. The fruit is a simple, dry achene (cypsela), ranging from brown to pale brown, tan, or straw-colored. It has an arcuate to linear shape, with a glabrous surface and ribbed or nerved texture. A pappus is present. It is found in summit bogs, occurring at an elevation of approximately 1,360 meters.