A densely hairy, greenish-gray herbaceous biennial. Flowers short, small, yellow, tubular, with 5 petal lobes; tightly packed in a terminal, usually unbranched, tall spike. Blooms May–September. During the first year, only a rosette of basal leaves forms. In the second year, the flower stalk rises, blooms, and sets seed, before the plant dies. The basal leaves persist during the winter, oblong, on petioles, to 1 foot long, extremely soft-hairy. Stem leaves are progressively smaller toward the top, with leaf tissue continuing into the stem.
Similar species: There are 4 species of Verbascum in Missouri. Moth mullein (V. blattaria) is common and weedy and is treated elsewhere in this guide. The other two are uncommon, introduced, and known only from single collections on highways or railroads: white mullein (V. lychnitis) in 1975, and clasping mullein (V. phlomoides) in 1915.