1 Flowers usually 1 per node throughout the inflorescence or with lowermost nodes with > 1 flower; inflorescences usually unbranched; leaves green and glabrous on both sides, or sparsely or densely pubescent with glandular hairs; hairs of the calyx and upper stem simple and glandular.

  2 Flowers purple, white, or yellow; bracteoles 0 on the pedicel; pedicels 5-20 (-25) mm long, longer than the calyx; glandular hairs sparse to absent on the leaves and the stems (and restricted to the upper stems).

    3 Flowers white or yellow; leaves gradually reduced in size upwards

    3 Flowers purple; leaves abruptly reduced in size in the upper half of the stem

1 Flowers mostly in axillary clusters of 2-10; inflorescences either branched or unbranched; leaves densely tomentose at least on the lower surface, and often the upper as well; hairs of the calyx and upper stem branched (dendritic), not glandular (except in V. sinuatum).

      4 Inflorescence generally simple (sometimes with 1-several small branches from near the inflorescence base), dense and spike-like (at least initially); leaves moderately to densely tomentose above (or glabrescent in V. nigrum ssp. nigrum); upper 3 filaments bearing white hairs (or all 5 bearing violet hairs in V. nigrum ssp. nigrum).

        5 Basal and lower stem leaves with blades basally cordate to nearly truncate; leaves sparsely tomentose to glabrate, quickly glabrescent abaxially, sometimes glabrate on both surfaces, thinly tomentose on abaxial leaf surface but not completely obscuring epidermis; all filaments villous with purple to violet hairs

        5 Basal and lower stem leaves with blades basally attenuate (V. thapsus) or distinctly petiolate (V. phlomoides); leaves densely and persistently tomentose on both surfaces; proximal filaments villous or glabrous, distal pair of filaments villous with yellowish to whitish hairs.

          6 Middle to upper stem leaves sessile to auriculate-clasping, slightly or not at all decurrent on the stem; stigma patulate, decurrent on the style; corollas white or yellow

          6 Middle to upper stem leaves sessile, decurrent down the stem to the next leaf; stigma capitate; corollas yellow.

             7 Corollas 30-55 mm in diameter; pellucid glands of the corolla absent or very few; anthers orange; pedicels adnate to the rachis or often free

             7 Corollas 14-20 (-30) mm in diameter, pellucid glands of the corolla numerous; anthers yellow; pedicels all or nearly all adnate to the rachis

      4 Inflorescence freely branched, paniculate (or unbranched or with few basal branches); leaves green and nearly glabrous above (or densely tomentose in V. sinuatum); all 5 filaments bearing either white, yellow, or violet hairs.

               8 Basal leaves lobed; upper leaf surface loosely to densely tomentose; filaments bearing violet hairs

               8 Basal leaves entire and unlobed; upper leaf surface glabrate; filaments bearing either white hairs or violet hairs.

                 9 Mid-stem leaves sessile to subsessile; filaments villous with white to yellow hairs

                 9 Mid-stem leaves distinctly petiolate, filaments villous with purple to violet hairs