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, plants not markedly glandular); plants not sticky to the touch	7
2	Mature berry orange, red or dark yellow; rare weed of disturbed places; North America	S. villosum
–	Mature berry green, purple or black; adventive, native or cultivated plants; North America, Mexico, and Central America	3
3	Calyx lobes enlarged in fruit and enclosing the berry; weeds of agricultural land; North America	4
–	Calyx lobes not enlarged and enclosing the berry; plants of open places or cultivated; Mexico and North America	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, no black or purple margins; berries pale green, not marbled with white, becoming matte, opaque, not marbled with white; stone cells 4–6, 0.8–1 mm in diameter	S. sarrachoides
5	Anthers to 2 mm long, usually less; fruit surface matte, with a glaucous cast; fruiting calyx lobes strongly reflexed; stone cells absent	S. retroflexum
–	Anthers more than 2 mm long; fruit surface more or less shiny, not glaucous or markedly matte; fruiting calyx lobes not strongly reflexed; stone cells present (2–6) or absent	6
6	Stone cells 4–6 in each berry; seeds ca. 1.5 mm long; inflorescence with flowers clustered near tip (sub-umbellate); glandular trichomes 0.5–2 mm long; Mexico, Central Volcanic Belt	S. pruinosum
–	Stone cells absent (rarely 2); seeds 1.8–2 mm long; inflorescence with flowers spaced along the rhachis; glandular trichomes to 0.5 mm long; North America, adventive	S. nigrum
7	Leaves deeply pinnatifid; prostrate herbs with fleshy leaves	S. triflorum
–	Leaves with entire or various toothed margins, but not deeply pinnatifid; plants erect or ascending (rarely prostrate with fleshy leaves [simple-leaved plants of S.triflorum])	8
8	Mature berries red or orange (green when immature)	9
–	Mature berries green, purple or black (green when immature)	10
9	Inflorescences 4–7 times branched; leaf margins entire, the leaves completely glabrous (occasionally sparsely ciliate); style ca. 2 mm long; anthers 0.8–1.5 (–1.8) mm long; stone cells 2, apical; central Mexico	S. corymbosum
–	Inflorescences unbranched (if branched merely forked); leaf margins toothed, the leaves pubescent, sometimes sparsely so; style > 2 mm long; anthers 1.8–2.2 mm long; stone cells absent; adventive in North America	S. villosum
10	Anthers less than or equal to 2 mm long	11
–	Anthers more than 2 mm long	13
11	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	12
12	Mature berry shiny black; corolla 3–6 mm in diameter, the lobes 2–3 mm long; leaves usually elliptic to ovate in outline; widespread, subtropical	S. americanum
–	Mature berry matte black with a glaucous cast; corolla 11–16 mm in diameter, the lobes 5–6 mm long; leaves rhomboid in outline; cultivated, rarely escaped	S. retroflexum
13	Buds narrowly ellipsoid to narrowly ovoid; corolla deeply stellate with narrowly triangular lanceolate lobes; berries shiny, with more than 10 stone cells	S. triflorum
–	Buds elliptic to ovoid to obovoid or elongate or globose (not narrow); corolla stellate with triangular to deltate lobes; berries matte or somewhat shiny, usually with fewer than 10 stone cells (but S.furcatum and S.nigrescens sometimes with more)	14
14	Stone cells in mature berries absent (occasionally 2); corolla less than 15 mm in diameter	15
–	Stone cells present in mature berries, always more than 2; corolla (10–)15–20 mm in diameter	18
15	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	16
16	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; adventive in North America	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	17
17	Peduncle in fruit 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 straight, 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
18	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	19
19	Anthers (2.7)3–4.5 mm long; corolla (10–)15–20 mm in diameter	20
–	Anthers less than 3 mm long; corolla less than 15 mm in diameter	21
20	Fruiting pedicels 15–17 mm long, strongly deflexed; anthers ellipsoid with straight sides; buds ellipsoid or subglobose; free portion of the filaments half the length of the anthers; cloud forests, Mexico to Panama, Caribbean	S. macrotonum
–	Fruiting pedicels 10–12 mm long, deflexed but not strongly so; anthers 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; montane and dry forests, southwestern United States to Nicaragua	S. douglasii
21	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, Caribbean, Mexico and Central America	S. nigrescens