Bracts and leaves of salvia carduacea
are prickly, partly lobed and hairy, hence the common name of thistle sage. Plants are found across the foothills and valleys of southern California, extending south into Baja California, and they vary in height from a few inches to several feet, depending on water and nutrient levels. Stems and foliage are covered by white, woolly hairs, most densely around the bracts subtending the flowers. True leaves are restricted to the base, and are also variable in length; usually up to 4 inches but sometimes up to three times this. Leaf margins are wavy, and bear sharp spines at quite widely-spaced intervals.
A single stem has up to four whorled clusters of flowers, at the tip and the upper nodes, subtended by spiny, spreading, lance-shaped bracts up to 2 inches long. The flowers have a spiny, lobed calyx and a large, lavender to purple (occasionally white) corolla, which opens widely to a two-lobed upper lip and a three-lobed lower lip. All lobes are fringed, some quite deeply. The corolla tube can be up to one inch in length. The stamens are exserted; they have purple filaments and red-orange anthers.