It is similar to other subspecies of Calothamnus quadrifidus except that its leaves are linear and somewhat rough and scaly and the stamen bundles are relatively long.

The lower half of the outer surface of the floral cup (the hypanthium) is hairy while the upper part is glabrous.

Flowering mainly occurs from August to December and is followed by fruits which are woody, roughly spherical capsules, 8–9 millimetres (0.31–0.35 in) long when mature.

seminudus was first formally described in 2010 by Alex George in Nuytsia from a specimen collected near Digger Rocks, north of Lake King.

seminudus occurs in the Ironcaps, Bremer Range and Peak Charles areas[1] in the Avon Wheatbelt, Coolgardie and Mallee biogeographic regions.