A difficult genus and collections should be of the entire plant, with main stems and larger leaves well represented. Internode pubescence should be checked at the middle of the stem.

1. Leaves densely white-woolly.

S. byzantina

1. Leaves variously pubescent to glabrous, but green and not white-woolly.

2. Leaves glabrous, sessile or subsessile, ± linear, entire to lightly toothed.

S. hyssopifolia

2. Leaves usually at least sparsely pubescent (at least beneath), sessile or petioled, lanceolate to ovate, regularly serrate.

3. Bractlets subtending individual flowers conspicuous, half as long to as long as the calyx tube (do not confuse the paired bracts at each node with the bractlets); leaves mostly in the lower half of the stem; basal rosettes of long-petiolate cordate leaves present.

S. officinalis

3. Bractlets subtending individual flowers minute, much less than half as long to as long as the calyx tube, or virtually absent; stem leafy to the inflorescence; basal rosettes absent.

4. Stem internodes pubescent on sides (at least 2) and angles; calyx pubescent throughout, sometimes including short gland-tipped hairs as well as longer ones.

5. Pubescence of stem angles and sides mostly spreading (note especially the smaller hairs on the sides).

S. pilosa

5. Pubescence of stem angles and sides mostly retrorse (note especially the smaller hairs on the sides).

6. Calyx, bracts, and inflorescence axis pubescent with mostly eglandular hairs, glandular hairs scattered and inconspicuous or essentially absent.

S. arenicola

6. Calyx, bracts, and inflorescence axis heavily stipitate-glandular as well as pubescent with straight hairs.

S. palustris

4. Stem internodes glabrous or pubescent only on the angles; calyx glabrous or pubescent (eglandular) primarily on the nerves and ciliate lobes.

7. Main stem leaves nearly sessile to very short petioled, petioles up to ca. 0.8 cm long; widest leaves ca. 1.2-1.8 cm wide.

S. aspera

7. Main stem leaves clearly petioled, the longest petioles (0.6-) 0.8-3 cm long; widest leaves ca. 1.5-4.2 cm wide.

8. Petioles and leaf blades (at least on the main veins beneath) hispidulous to hispid; longer petioles (0.6-) 0.8-1.5 (-2.4) cm long; widespread.

S. hispida

8. Petioles and leaf blades glabrous or nearly so; longer petioles 1.3-3 cm long; southern Lower Peninsula.

S. tenuifolia