Solanaceae, the Nightshade Family
Herbs or shrubs, with alternate leaves and regular or slightly irregular flowers; sepals 5, united; corolla of 5 united petals, bearing the 5 stamens attached; ovary 1, 2-5 (usually 2)-celled, with a slender style.
| 1a. Corolla rotate; anthers close together (flowers in summer) — 2. | |
| 1b. Corolla not rotate; anthers separate — 5. | |
| 2a. Stem and leaves prickly (3-8 dm. high) — 3. | |
| 2b. Stem and leaves not prickly — 4. | |
| 3a. Flowers white or bluish | Horse Nettle, Solanum carolinense. |
| 3b. Flowers yellow | Buffalo Bur, Solanum rostratum. |
| 4a. Climbing vine; leaves frequently lobed (flowers blue) | Bittersweet, Solanum dulcamara. |
| 4b. Not climbing; leaves toothed (flowers white) | Nightshade, Solanum nigrum. |
| 5a. Climbing or trailing shrub, with purplish, white, or greenish flowers about 1 cm. wide (frequently thorny; flowers in summer) | Matrimony Vine, Lycium halimifolium. |
| 5b. Herbaceous plants, not climbing — 6. | |
| 6a. Flowers white, red, or blue, 2.5 cm. or more wide (summer) — 7. | |
| 6b. Flowers yellow, yellowish-white, or greenish-yellow (summer) — 12. | |
| 7a. Corolla-tube 10 cm. long or more (5-12 dm. high) — 8. | |
| 7b. Corolla-tube 5 cm. long or less — 10. | |
| 8a. Stem finely pubescent; leaves entire or nearly so | Thorn-apple, Datura metel. |
| 8b. Stem glabrous; leaves coarsely toothed (Jimson Weed) — 9. | |
| 9a. Stem green; corolla white | Jimson Weed, Datura stramonium. |
| 9b. Stem purple; corolla light-blue or purple | Jimson Weed, Datura tatula. |
| 10a. Corolla pale-blue (5-10 dm. high) | Apple of Peru, Nicandra physalodes. |
| 10b. Corolla, red or violet (2-4 dm. high) | Petunia, Petunia violacea. |
| 10c. Corolla white — 11. | |
| 11a. Corolla all white (2-4 dm. high) | Petunia, Petunia axillaris. |
| 11b. Corolla with yellow center | White Ground Cherry, Physalis grandiflora. |
| 12a. Corolla 30 mm. wide or more, somewhat irregular; stamens declined to one side (3-6 dm. high) | Henbane, Hyoscyamus niger. |
| 12b. Corolla smaller, strictly regular — 13. | |
| 13a. Flowers in terminal panicles; corolla tubular, with slightly spreading lobes (5-10 dm. high) | Wild Tobacco, Nicotiana rustica. |
| 13b. Flowers solitary in the axils; corolla short, widely spreading (3-8 dm. high) (Ground Cherry) — 14. | |
| 14a. Annuals with branching slender roots — 15. | |
| 14b. Perennials with thickened roots and rootstocks — 16. | |
| 15a. Plants pubescent | Ground Cherry, Physalis pubescens. |
| 15b. Plants smooth, or with a few scattered hairs | Ground Cherry, Physalis ixocarpa. |
| 16a. Stem viscid-pubescent | Ground Cherry, Physalis heterophylla. |
| 16b. Stem glabrous or slightly pubescent, not viscid — 17. | |
| 17a. Leaves and stem distinctly pubescent | Ground Cherry, Physalis virginiana. |
| 17b. Leaves and stem almost glabrous | Ground Cherry, Physalis subglabrata. |