The mulleins of my youth were plants of the somewhat-brutish Verbascum thapsus. Verbascum nigrum, or black mullein, seems to be something of a more delicate species. Occasionally planted in gardens despite its short life (often a biennial, sometimes short-lived perennial), it grows to 1m (3 ft.) in height.
Both species share a preference for dry, open areas–prehaps not surprising when you consider the centre of diversity for this genus of ~250 species is in the Mediterranean. Verbascum nigrum, however, has a range that spans most of Europe (Mediterranean or not) and parts of Asia (including Siberia). Like Verbascum thapsus, Verbascum nigrum has found an additional home in North America, though it is not nearly so widespread as the former. The success of the species when introduced into an area is due in part to its prolific seed production; an individual plant can generate seventy thousand seeds in one season.