1 Plant an herb, 0.5-3 m tall; stems and leaf blades densely viscid-puberulent (or sparsely so to merely tuberculate in N. longiflora).

  2 Corolla tube 1.2-1.7 cm long, greenish yellow, with limb 3-6 mm wide; leaves distinctly petiolate; [section Rusticae]

  2 Corolla tube 2.5-12.0 cm long, cream, white, yellow, or pink, with limb 10-25 mm wide; leaves auriculate clasping.

    3 Larger leaves on a plant 3.5-8 dm long; corolla tube 3.0-5.5 cm long, 4-7× as long as the average diameter, the limb 10-15 mm wide, pink or reddish (rarely white); [section Nicotiana]

    3 Larger leaves on a plant 1-3 (-5) dm long; corolla tube 2.5-12.0 cm long, 10-50× as long as the average diameter, the limb 15-25 mm wide, white or lavender.

      4 Rosette of a few leaves, not persisting; cauline leaves clasping and decurrent on the stem; [section Alatae]

      4 Rosette persisting; cauline leaves clasping or auriculate, but not decurrent on the stem.

        5 Corolla tube 2.5-3.5 cm long; [section Alatae]

        5 Corolla tube 4-12 cm long.

          6 Corolla throat constricted; filaments unequal, stamens didynamous (2 different lengths); cauline leaf blades lanceolate or linear, leaves sessile, auriculate; [section Alatae]

          6 Corolla throat gaping; filaments equal, fused to corolla along their entire length, anthers appearing sessile; cauline leaf blades pandurate and clasping; [section Repandae]

1 Leaves all basal, from creeping rhizomes; corolla white; [subfamily Solanoideae].

  2 Leaves broadly elliptical, rounded at the base; corolla lobes > 2× as long as wide, attenuate at the tip; [tribe Jaboroseae]

  2 Leaves ovate, strongly cordate at the base; corolla lobes < 1.5× as long as broad, obtuse (acute) at the tip; [tribe Capsiceae]

1 Leaves all or mainly cauline.

    3 Plant distinctly woody, an upright shrub or scrambling vine.

      4 Corolla ≥ 16 cm long.

        5 Plants vines

        5 Plants large shrubs to small trees

      4 Corolla < 16 cm long.

          6 Flowers white or yellow, the tube > 6× as long as its diameter; fruit either a white berry, or a capsule.

             7 Fruit a white, purple, or black berry; [subfamily Cestroideae; tribe Cestreae]

          6 Flowers lavender or blue, the tube < 3× as long as its diameter; fruit a red, orange, or yellow berry; [subfamily Solanoideae].

               8 Leaves 0.5-7 cm long, 0.2-3.5 cm wide; [tribe Lycieae]

               8 Leaves 10-30 cm long, 4-14 cm wide; [tribe Solaneae]

    3 Plant herbaceous (some taxa keyed here can be robust and tough-stemmed, but are herbaceous, lacking overwintering buds on aerial stems).

                 9 Corolla salverform or narrowly funnel-shaped, with a well-developed tubular portion, this > 1 cm long (except in Calibrachoa) and either flared or essentially isodiametric and > 4× as long as its midpoint diameter, the limb expanding more or less abruptly from the tubular portion; fruit a capsule opening by longitudinal valves or by apical pores.

                   10 Corolla 7-25 cm long, white, pale blue or pale pink; capsule spiny, 3-5 cm long, subtended by a collar formed by the reflexed corolla base; [subfamily Solanoideae; tribe Datureae]

                   10 Corolla 0.6-7 cm long, white, blue, pink, or other colors; capsule smooth, not collared.

                     11 Flowers solitary, axillary; [subfamily Petunioideae].

                       12 Leaves linear to narrowly spatulate

                       12 Leaves oblong, ovate or elliptic

                     11 Flowers in (2-) 3-many flowered racemes or panicles.

                          13 Calyx accrescent in fruit, wholly or partly surrounding the capsule; corolla lavender to blue, with a whitish center; flower bilaterally symmetrical; stamens 4; [subfamily Cestroideae; tribe Browallieae]

                          13 Calyx not accrescent, subtending the mature fruit; corolla white, pink, green, pink, or blue; flower radially symmetrical; stamens 5.

                            14 Leaves broad, > 4 cm wide; corolla tube 1.5-12.0 cm long; [subfamily Nicotianoideae]

                            14 Leaves narrow, linear to narrowly oblancolate, to 0.5 mm wide; corolla tube 1.0-1.4 cm long; [subfamily Petunioideae]

                 9 Corolla either urceolate, campanulate, or rotate, lacking a narrow tubular portion that is both > 1 cm long and > 4× as long as its midpoint diameter; fruit a berry (or circumscissile capsule in Hyoscyamus); [subfamily Solanoideae].

                              15 Fruit a circumscissile capsule; calyx accrescent, nearly enclosing the fruit; corolla cream to yellow, with a maroon center; inflorescence a strongly secund raceme; [tribe Hyoscyameae]

                              15 Fruit a berry (hollow in Capsicum); calyx either accrescent around the fruit or not (and then subtending the fruit); corolla various (but not as above, though in some Physalis yellow and with each petal marked with a purple or maroon spot); inflorescence various.

                                16 Calyx not accrescent, subtending the mature berry.

                                  17 Berries 1.0-2.5 cm long; corolla urceolate (at least slightly constricted at the ‘neck’, just below the lobes of the corolla).

                                    18 Berries nearly spherical, blue-black, 1.0-2.0 cm long, 1.0-2.0 cm in diameter; corolla 2-3 cm long, maroon or purple, and greenish towards the base; plant an upright herb; [tribe Hyoscyameae]

                                    18 Berries elliptical, yellow, 1.5-2.5 cm long, 0.8-1.5 cm in diameter; corolla white 0.7-1.0 cm long, white; plant a trailing or scrambling vine; [tribe Physaleae]

                                  17 Berries 0.3-25 cm long.

                                       19 Locules air-filled; berries usually elongate and irregularly shaped (sometimes ovoidal or spherical; [peppers, chilies]; [tribe Capsiceae]

                                       19 Locules fleshy; berries spherical or ellipsoidal; [nightshades, tomato, potato, eggplant]; [tribe Solaneae]

                                16 Calyx accrescent, wholly or partly surrounding the mature berry.

                                         20 Mature calyx spiny; [tribe Solaneae]

                                         20 Mature calyx glabrous or with hairs.

                                           21 Calyx divided nearly to the auricled base; corolla blue; [tribe Nicandreae]

                                           21 Calyx fused nearly to its summit; corolla white or yellow; [tribe Physalinae].

                                             22 Fruiting calyx bright red (fresh or dry); corolla white; [cultivated and weakly naturalized near gardens]

                                             22 Fruiting calyx green, yellow, or orange, drying brown or tan; corolla yellow, often marked with 5 large maroon or purple spots in the throat; [collectively widespread].

                                               23 Flowers 2 or more per leaf axil; berries with spherical seed-like bodies intermixed with the flattened, reniform seeds; [of the Gulf Coastal Plain]

                                               23 Flowers 1 per leaf axil; berries with flattened, reniform seeds only; [collectively widespread]