1	Foliage with glandular trichomes, the plants sticky to the touch	2
–	Foliage lacking glandular trichomes (sometimes with a few scattered trichomes with glandular tips, not markedly glandular); plants not sticky to the touch	6
2	Mature berry orange, red or dark yellow, usually somewhat ellipsoid; calyx lobes with translucent sinuses; rare weed of disturbed places	S. villosum
–	Mature berry green, purple or black, usually globose or subglobose; widespread weedy species	3
3	Calyx lobes enlarged in fruit and enclosing the berry	4
–	Calyx lobes not enlarged and enclosing the berry	5
4	Leaf bases attenuate to cuneate; inflorescences mostly internodal, with 4–8 (–10) flowers; corolla with a central greenish yellow star with black or purple margins; berries dark green to greenish brown, marbled with white, becoming translucent and shiny; stone cells 1–3, ca. 0.5 mm in diameter	S. nitidibaccatum
–	Leaf bases cordate or truncate; inflorescences mostly leaf-opposed, with 2–5 (–7) flowers; corolla with a central greenish yellow star without black or purple margins; berries pale green, not marbled with white, becoming matte, opaque; stone cells 4–6, 0.8–1 mm in diameter	S. sarrachoides
5	Inflorescences with the flowers clustered near the tips; anthers 1.1.3–1.8 mm long; mature berry matte with a glaucous cast; seeds 1.3–1.5 mm long; cultivated	S. retroflexum
–	Inflorescences with flowers spaced along the rhachis; anthers 1.8–2.5 mm long; mature berry matte, but not glaucous; seeds 1.8–2 mm long; adventive	S. nigrum
6	Leaves deeply pinnatifid; prostrate herbs with fleshy leaves	S. triflorum
–	Leaves with entire or various toothed margins, not pinnatifid; plants erect or scrambling (rarely prostrate, if so the leaves fleshy)	7
7	Mature berry orange, red or dark yellow (shiny and translucent at maturity); calyx lobes with translucent sinuses; rare weed of disturbed places	S. villosum
–	Mature berries green, purple or black; calyx lobes without translucent sinuses; various habitats	8
8	Anthers less than or equal to 2 mm long	9
–	Anthers more than 2 mm long	10
9	Mature berries dropping with the pedicel; calyx lobes appressed to spreading in fruit; stone cells more than 4, usually 8 per berry; eastern and central North America	S. emulans
–	Mature berries dropping without the pedicel; calyx lobes strongly reflexed in fruit; stone cells absent or at most 2(4); widespread and subtropical or cultivated	11
10	Mature berry shiny; corolla 3–6 mm in diameter, the lobes 2–3 mm long; widespread, subtropical	S. americanum
–	Mature berry matte with a glaucous cast; corolla 11–16 mm in diameter, the lobes 5–6 mm long; cultivated, rarely escaped	S. retroflexum
11	Buds narrowly ellipsoid to narrowly ovoid; corolla deeply stellate with narrowly lanceolate strap-like lobes; berries shiny, with more than 10 stone cells; prostrate herbs	S. triflorum
–	Buds ellipsoid to ovoid to obovoid; corolla stellate with triangular to deltate lobes, not markedly lanceolate and strap-like; berries matte or somewhat shiny, usually with fewer than 10 stone cells; erect or straggling herbs	12
12	Stone cells in mature berries absent (occasionally 2); corolla less than 15 mm in diameter	13
–	Stone cells present in mature berries, always more than 2; corolla (10-)15–20 mm in diameter	16
13	Berries 10–20 mm in diameter, shiny, slightly flattened; fruiting pedicels strongly spreading; anthers somewhat tapering, often drying brownish orange; cultivated	S. scabrum
–	Berries less than 15 mm in diameter, somewhat shiny, matte or slightly glaucous, globose; fruiting pedicels weakly spreading or more usually deflexed; anthers ellipsoid, not drying brownish orange; native, adventive, or naturalised	14
14	Inflorescences with the flowers spaced along the rhachis; anthers 1.8–2.5 mm long; fruiting pedicels spreading; berry surface slightly shiny; seeds 1.8–2 mm long; sporadically adventive, most commonly along east and west coasts	S. nigrum
–	Inflorescences with the flowers clustered at the tips (sub-umbelliform), only a few spaced along the rhachis; anthers more than 2 mm long; fruiting pedicels deflexed, usually strongly so; berry surface matte or glaucous; seeds 1–1.5 mm long; native or adventive	15
15	Peduncle in fruit at right angles or more usually strongly deflexed downwards; berries 4–9 mm in diameter; calyx lobes appressed to surface of berry in fruit; styles exserted to 1.5 mm from the anther cone at anthesis; adventive in North America	S. chenopodioides
–	Peduncle in fruit slightly ascending, not deflexed downward; berries 8–14 mm in diameter; calyx lobes reflexed in fruit; style exserted 2–2.5 mm from the anther cone at anthesis; coastal habitats, southeastern United States	S. pseudogracile
16	Buds globose or subglobose; style long-exserted from anther cone, even in bud; inflorescences usually forked; western North America	S. furcatum
–	Buds ellipsoid or ovoid; style exserted from the anther cone, but not in bud; inflorescences usually unbranched; widespread	17
17	Anthers (2.7)3–4.5 mm long, slightly tapering to the tip; buds ovoid, tapering to the apex; free portion of the filaments minute, ca. 1/4 the length of the anther; corolla to 20 mm in diameter; montane and dry forests, southwestern United States	S. douglasii
–	Anthers less than 3 mm long, ellipsoid with straight sides; buds ellipsoid; free portion of the filaments half the length of the anthers; corolla less than 15 mm in diameter; east of the Rocky Mountains	18
18	Basal flower in the inflorescence with the articulation above the rhachis; calyx lobes unequal, lanceolate, the longest one 1.7–4.5 mm long; seeds 1.8–2 mm long; stone cells 2–4; prairies and open woodlands, midwestern United States	S. interius
–	All flowers with the articulation at the inflorescence rhachis; calyx lobes equal, deltate, 0.5–1 mm long; seeds 1.2–1.5 mm long; stone cells usually more than 5; forests and coastal areas, southeastern United States	S. nigrescens