This is a large Eurasian genus (ca. 250 species); all our species are adventive or escapes from cultivation, and identification of the uncommon ones is to some extent tentative. Hybrids are frequent in Verbascum, generally intermediate between their parents as distinguished in the key below.
1. Flowers one in axil of each bract, on a pedicel about equaling or exceeding the bract; leaves and stems at middle of plant glabrous or nearly so (upper portion often with sparse stalked or sessile glands).
1. Flowers mostly 2 or more in axil of each bract, on pedicels shorter than the bracts; leaves and stem ± densely stellate-pubescent, not glandular.
2. Upper cauline leaves only slightly if at all decurrent.
3. Calyx 2.5–4 mm long, shorter than the longest pedicels; corolla less than 2 cm broad; pubescence of stems and upper surface of leaves ± thin, readily deciduous at maturity, leaving green surface; stem angled or ridged, especially above.
3. Calyx ca. 5.5–8 mm long, exceeding the pedicels; corolla over 3 cm broad; pubescence of stems and both surfaces of leaves very dense, persistent; stems not angled.
2. Upper cauline leaves decurrent, with a narrow wing running halfway to all the way to the next lower node.
4. Stigma shortly decurrent down the style; lower bracts and upper leaves ± caudate (abruptly narrowed to prolonged tip); corolla ca. 3–5 cm broad, very flat.
4. Stigma strictly terminal, across the apex of the style; lower bracts and leaves not caudate (at most acuminate); corolla ca. 1.2–2.5 (–2.8) cm broad, ± concave.