Thamnosma montana is a distinctive species of the Sonoran and Mojave deserts. All plant parts are densely gland-dotted. The thick, much branched, yellowish-green stems bear small, simple leaves at alternate intervals, and persist only during spring; for the rest of the year the stems are leafless, resembling a species of broom.
The urn-shaped flowers consist of four small, blunt-pointed sepals, fused for about half their height, and a purple, four-lobed corolla, around 0.4 inches long. The corolla lobes tend to stay pressed together, opening only at the (reflexed) tips, to reveal eight anthers (four held above the others) and a two-lobed style. Fruits are two-lobed green capsules, each lobe unevenly spherical.