Most species are known or reputed to be poisonous, and even potatoes that have turned green when exposed to light should be thoroughly boiled (discarding the water) before eating. Toxicity varies, and may be less in fully ripe fruits, but experimenting with unfamiliar Solanum fruits is not recommended. All our species are herbaceous annuals or perennials except for S. dulcamara, which is a climbing soft-wooded vine or scrambling shrub.

1. Plants spiny or prickly; pubescence of stems and leaves otherwise all or mostly stellate.

2. Calyx without spines (may be coarsely stellate-hairy), not enclosing the berry; corolla white to purple; leaves simple, with only an irregularly sinuate or coarsely toothed margin; perennial with deep, often rhizome-like roots.

S. carolinense

2. Calyx spiny, fully enclosing the berry when mature; corolla yellow; leaves very deeply lobed or even compound; tap-rooted annual.

S. rostratum

1. Plants without spines or prickles; pubescence of simple hairs.

3. Corolla yellow; anthers opening by longitudinal slits.

S. lycopersicum

3. Corolla white or purple; anthers opening by terminal pores.

4. Plant a subshrubby perennial vine, with elongate sprawling or climbing stems; corolla purple (occasionally albino); fruit red at maturity.

S. dulcamara

4. Plant an erect (straight or bushy) herbaceous annual; corolla white; fruit green or black at maturity.

5. Leaves ± irregularly toothed or sinuate (or occasionally entire), neither compound nor lobed.

6. Plant (especially stems and inflorescence) covered with ± dense, spreading, multicellular, glandular hairs; mature fruit dark green to green-brown, ca. half covered by the calyx.

S. physalifolium

6. Plant glabrate, at most sparsely pubescent with very short ± appressed eglandular hairs; mature fruit black, scarcely if at all covered by the calyx.

S. ptychanthum

5. Leaves pinnately compound or lobed at least halfway to the midrib.

7. Corolla less than 1 cm broad; leaves pinnately lobed; plant without tubers, usually fruiting copiously.

S. triflorum

7. Corolla more than 1 cm broad; leaves pinnately compound (tiny leaflets alternating with much larger ones); plant with large underground tubers (potatoes), only rarely fruiting.

S. tuberosum