Solanum
Sp. Pl. 1: 184. 1753.
Herbs, vines, subshrubs, shrubs, or trees, annual or perennial, sometimes rhizomatous or with tubers, unarmed or prickly, glabrous or pubescent, hairs simple, dendritically branched, or stellate, glandular or eglandular [peltate scales]. Stems erect to prostrate or twining, with sympodial growth. Leaves alternate, petiolate or sessile; blade simple or pinnately compound, margins entire, sinuate-dentate, dentate, or toothed to pinnately lobed or divided. Inflorescences terminal, leaf-opposed, extra-axillary, or in branch forks, branched or unbranched. Flowers usually bisexual, 5-merous; calyx sometimes accrescent, campanulate, truncate to 5-lobed; corolla white, cream, green, yellow, pink, blue, violet, or purple, radially or bilaterally symmetric, rotate, rotate-stellate, campanulate, stellate-pentagonal, or stellate, shallowly to deeply 5-lobed; stamens inserted near base of corolla, equal or unequal; anthers oblong, ellipsoidal, or lanceolate, broad or narrow and tapering toward the apex, dehiscing by pores, these sometimes expanding into longitudinal slits; ovary 2-carpellate (sometimes multicarpellate in cultivated species); style straight or curved, stigma truncate to capitate. Fruits berries, globose to ellipsoidal or ovoid, fleshy or juicy (occasionally dry), with sclerotic granules in some species. Seeds usually reniform, flattened, plump, or rounded, occasionally angled. x = 12.
Distribution
nearly worldwide on all continents except Antarctica.
Discussion
Species ca. 1500 (52 in the flora).
Solanum is the largest genus in the Solanaceae and one of the largest genera of angiosperms. It is the most speciose genus in the family in North America. The North American taxa are composed of natives, most of which have ranges that extend into Mexico or the Caribbean, and a number of species that have been introduced deliberately or unintentionally. Some of these have spread and become naturalized, occasionally as pests, whereas others are only sporadically or ephemerally escaped from cultivation.
Solanum is one of the world’s most economically important genera. It includes crop plants such as the potato, tomato, and eggplant as well as species used on a small scale as edible fruits or as ornamentals. Most Solanum plants contain high levels of alkaloids and can be toxic. In general, the foliage or unripe fruits of Solanum species should not be consumed by humans or other animals due to danger of poisoning.
Sclerotic granules (also called stone cells) occur in fruits of some Solanum species. These are hardened masses within the fruit pulp that are usually spherical, 0.5–5 mm in diameter, and visible with 10× magnification. In dissected fruits they are generally paler, rounded, and more homogeneous in appearance than the seeds. The number of sclerotic granules per fruit can be diagnostic in species of the black nightshade group. They are very numerous in S. laciniatum and S. triflorum and can be seen in pressed fruits without dissection.
Some Solanum species are cultivated as foods or ornamentals and may occasionally escape, while other non-native species are known only from historical records.
The potato (Solanum tuberosum Linnaeus) is the world’s leading root crop and second only to the cereal grains in food production. Potatoes are widely cultivated in agricultural fields and home gardens. Volunteer plants of potato can grow from discarded tubers but do not appear to persist or spread. Eggplants (S. melongena Linnaeus) are commonly grown in home gardens or as specialty vegetables in small-scale agriculture. They may occasionally escape from cultivation in southern Florida but have not become naturalized. Solanum retroflexum Dunal (sunberry, wonderberry) and S. scabrum Miller (garden huckleberry) are sometimes grown for their edible fruits but apparently do not escape from cultivation. Solanum glaucophyllum Desfontaines is known in the United States only from two specimens collected in Pensacola, Florida, over a hundred years ago. Solanum pilcomayense Morong, native to Argentina and Paraguay, is only known from two collections made in port areas in New Jersey and Texas, but it has also not been collected since the early 20th century and is not established. Solanum villosum Miller (hairy nightshade, woolly nightshade) is an occasional introduction from the Old World but has not persisted or become naturalized in North America. It was first recorded in the United States in 1899 in Pensacola, Florida, perhaps arriving in ships’ ballast. After this manuscript was completed, S. houstonii Martyn (syn. S. tridynamum Dunal) was discovered in Santa Cruz County, Arizona. This species was formerly considered endemic to Mexico (S. Knapp et al. 2017). It is most similar to S. hindsianum but differs in its dimorphic hermaphroditic and staminate flowers with strongly unequal anthers in the latter.
The North American Solanum flora includes a number of species in the black nightshade group (Solanum sect. Solanum, or the Morelloid clade). These can form hybrid and polyploid complexes and are notoriously difficult to identify. Previous floras have used erroneous names or conflated several species under a single name, often referring to all black nightshades in an area as S. americanum or S. nigrum. Many of the older determinations of specimens in herbaria should be considered suspect. The North American black nightshade species comprise natives and endemics (for example, S. emulans, S. interius, S. pseudogracile) as well as introduced or adventive species from Central and South America and the Old World. This is still a difficult group under active study. T. Särkinen et al. (2018) includes complete descriptions, nomenclature, and synonymy for taxa treated here that have been introduced from the Old World. S. Knapp et al. (2019) similarly treated the black nightshade species of North and Central America and the Caribbean.
Selected References
None.
Lower Taxa
Key
| 1 | Plants usually with prickles (at least on basal parts or on young plants) and usually with stellate hairs (except in S. capsicoides); anthers narrow and tapered, dehiscent by terminal pores. | > 2 |
| 2 | Leaves 1–3 times deeply pinnatifid (divided more than halfway to midrib) to compound; fruits nearly to completely covered by accrescent prickly calyx. | > 3 |
| 3 | Corollas radially symmetric; stamens equal or nearly so; calyces loosely covering red, juicy fruits. | Solanum sisymbriifolium |
| 3 | Corollas bilaterally symmetric; stamens dimorphic, with one much longer than others; calyces tightly covering brown, dry fruits. | > 4 |
| 4 | Stem hairs stellate or otherwise branched; corollas yellow. | Solanum rostratum |
| 4 | Stem hairs mostly simple, often glandular (sometimes mixed with sparse stellate hairs); corollas violet, blue, white, or yellow. | > 5 |
| 5 | Corollas white or yellow. | > 6 |
| 6 | Stems with well-spaced, needlelike prickles; corollas white, 2–2.5 cm diam., rotate-stellate, with abundant interpetalar tissue; w Texas. | Solanum cordicitum |
| 6 | Stems with dense, bristlelike prickles; corollas yellow, 1.3–1.8 cm diam., stellate, with sparse interpetalar tissue; s Arizona. | Solanum lumholtzianum |
| 5 | Corollas violet or blue. | > 7 |
| 7 | Corollas 1–1.5 cm diam.; long anther 2–5 mm. | > 8 |
| 8 | Stems densely pubescent with simple, glandular hairs 0.2–0.4 mm; stems sparsely to moderately prickly, with 20 or fewer prickles per cm; corollas pentagonal-stellate, with sparse interpetalar tissue; endemic to nc New Mexico. | Solanum novomexicanum |
| 8 | Stems sparsely pubescent with simple, glandular hairs ca. 0.2 mm; stems densely prickly, with 30+ prickles per cm; corollas pentagonal, with abundant interpetalar tissue; w Texas to c New Mexico, Arizona. | Solanum setigeroides |
| 7 | Corollas 1.4–3.5 cm diam.; long anther 5.5–20 mm. | > 9 |
| 9 | Plants perennials; seeds plump, 2.8–3.6 mm. | Solanum tenuipes |
| 9 | Plants annuals; seeds flattened, 2.3–3 mm. | > 10 |
| 10 | Long anther 11–16 mm; corollas 2.5–3.5 cm diam.; large leaves usually only 2 times pinnatifid, with obtuse to rounded ultimate lobes. | Solanum citrullifolium |
| 10 | Long anther 5.5–8.5 mm; corollas 1.4–2 cm diam.; large leaves often 3 times pinnatifid, with acute ultimate lobes. | Solanum davisense |
| 2 | Leaves entire or lobed, rarely deeply pinnatifid or compound; fruiting calyces not accrescent or, if accrescent, not almost completely covering fruits. | > 11 |
| 11 | Leaves sessile or with petiole to 1 cm, blade rhombic; calyx lobes linear; corollas to 1–2 cm diam.; c Florida. | Solanum jamaicense |
| 11 | Leaves with petiole (0.1–)1–10(–13) cm, blade lanceolate to oblong, elliptic, ovate, obovate, or suborbiculate; calyx lobes linear-lanceolate, lanceolate, triangular, deltate, ovate-lanceolate, elliptic-acuminate, or broadly deltate; corollas (1–)1.5–5 cm diam. | > 12 |
| 12 | Pubescence of stems and upper leaf surfaces of unbranched hairs or plants glabrate. | > 13 |
| 13 | Pubescence eglandular or plants glabrate; berries orange to red; seeds winged. | Solanum capsicoides |
| 13 | Pubescence glandular and eglandular; berries yellow, often mottled with green when young; seeds not winged. | Solanum viarum |
| 12 | Pubescence of stem and upper leaf surfaces of stellate hairs. | > 14 |
| 14 | Pubescence dense and silvery or bright white, particularly on lower leaf surfaces. | > 15 |
| 15 | Stellate hairs scalelike, with rays fused at center. | Solanum elaeagnifolium |
| 15 | Stellate hairs not scalelike, rays all separate. | > 16 |
| 16 | Leaves (0.5–)1–3(–4.5) cm wide. | Solanum hindsianum |
| 16 | Leaves 3–15 cm wide. | > 17 |
| 17 | Calyces not prickly; inflorescences usually much-branched; corollas usually blue to purple, rarely whitish; berries 0.7–1.5 cm diam., yellow to orange. | Solanum lanceolatum |
| 17 | Calyces prickly; inflorescences unbranched or forked; corollas white to pale purple; berries 3.5–4(–5) cm diam., yellow. | Solanum marginatum |
| 14 | Pubescence sparse to dense, of various colors, but not noticeably silvery or bright white. | > 18 |
| 18 | Scandent shrubs with branches 1–2+ m; stems glabrate to sparsely pubescent; wet areas in Florida and Texas. | Solanum tampicense |
| 18 | Erect or spreading herbs, shrubs, or small trees; stems noticeably stellate-pubescent; widespread, including Florida and Texas. | > 19 |
| 19 | Leaf margins entire to very shallowly lobed; corollas stellate, without interpetalar tissue; berries red. | > 20 |
| 20 | Inner surface of anther tube densely stellate-pubescent; inflorescences usually unbranched; pedicels recurved to one side of axis in fruit. | Solanum bahamense |
| 20 | Inner surface of anther tube glabrous; inflorescences branched; pedicels erect in fruit. | Solanum donianum |
| 19 | Leaf margins usually shallowly to deeply lobed, rarely entire, subentire, or sinuate; corollas rotate-campanulate, rotate-stellate, stellate-pentagonal, or stellate, with sparse to abundant interpetalar tissue; berries green, yellow, or purplish. | > 21 |
| 21 | Trees or shrubs 1–4 m; inflorescence pubescence of unbranched glandular hairs. | Solanum torvum |
| 21 | Erect or spreading annual or perennial herbs or shrubs 0.2–1.2 m; inflorescence pubescence stellate. | > 22 |
| 22 | Stems, inflorescences, and calyces densely armed; annual herbs, usually spreading and to 0.5(–1) m; major leaf lobes with acute teeth or shallow lobes. | Solanum campechiense |
| 22 | Stems, inflorescences, and calyces sparsely to moderately armed; erect perennial herbs or shrubs 0.2–1.2 m; major leaf lobes, if present, entire to coarsely lobed. | > 23 |
| 23 | Stems and petioles stellate-pubescent with central ray 1-celled and equal to or shorter than lateral rays. | Solanum dimidiatum |
| 23 | Stems and petioles stellate-pubescent with central ray 1–5-celled and longer than lateral rays. | > 24 |
| 24 | Plants to 0.2 m; leaf margins entire, sinuate, or shallowly lobed; inflorescences 1–4-flowered; endemic to dolomite outcrops in Alabama and possibly Georgia. | Solanum pumilum |
| 24 | Plants to 1.2 m; leaf margins subentire, sinuate, or shallowly to deeply lobed; inflorescences 2–15-flowered; plants not confined to dolomite outcrops and distributions more widespread. | > 25 |
| 25 | Stems armed with prickles to 6 mm; inflorescences unbranched or rarely forked; corollas 2–3 cm diam.; widespread in North America. | Solanum carolinense |
| 25 | Stems armed with prickles to 15 mm; inflorescences forked to several times branched; corollas 2–4.4 cm diam.; mainly Alabama, Florida, and Georgia, rarely Mississippi. | Solanum perplexum |
| 1 | Plants without prickles, with or without stellate hairs; anthers of various forms, dehiscent by terminal pores that often open into longitudinal slits or by introrse longitudinal slits. | > 26 |
| 26 | Leaves compound; pedicels articulated above base. | > 27 |
| 27 | Leaflets lobed; corollas yellow; plants without tubers; berries usually red, orange, or yellow. | Solanum lycopersicum |
| 27 | Leaflets entire; corollas white to pink, blue, or purple; plants with underground tubers; berries green. | > 28 |
| 28 | Corollas white, stellate; pseudostipules (when present) pinnatifid. | Solanum jamesii |
| 28 | Corollas purple, blue, pale pink, or rarely white, pentagonal to rotate; pseudostipules entire. | Solanum stoloniferum |
| 26 | Leaves simple, entire, undulate, sinuate-dentate to toothed, deeply lobed, pinnatifid, or hastate, simple to pinnately compound in S. seaforthianum; pedicels articulated at base. | > 29 |
| 29 | Plants climbing or scrambling vines. | > 30 |
| 30 | Stamens (filaments) unequal; corollas purple; most leaves lobed or compound with up to 4 pairs of leaflets. | Solanum seaforthianum |
| 30 | Stamens equal; corollas white or purple; leaves unlobed or with 1–3 basal lobes. | > 31 |
| 31 | Corollas purple (rarely white) with green and white shiny spots at base of each lobe; n 2/3 of United States, s Canada. | Solanum dulcamara |
| 31 | Corollas white or tinged with purple, often with shiny green or greenish white eye; Texas. | Solanum triquetrum |
| 29 | Plants herbs, subshrubs, shrubs, or small trees, not climbing. | > 32 |
| 32 | Shrubs or small trees, 2–12 m; ovaries and berries pubescent. | > 33 |
| 33 | Corollas white; without small axillary leaves. | Solanum erianthum |
| 33 | Corollas purple; larger leaves often with smaller axillary leaves. | Solanum mauritianum |
| 32 | Herbs, subshrubs, shrubs, or small trees, 0.1–2(–4) m; ovaries and berries glabrous. | > 34 |
| 34 | Corollas 3–5 cm diam., usually pink to blue, violet, or purple, rarely whitish; shrubs or small trees, 1–4 m. | > 35 |
| 35 | Plants densely pubescent with usually glandular hairs; Santa Catalina Island, California. | Solanum wallacei |
| 35 | Plants glabrous; California, Oregon. | > 36 |
| 36 | Corolla lobes acute at apex; berries orange to red, sclerotic granules inconspicuous to absent. | Solanum aviculare |
| 36 | Corolla lobes notched at apex; berries yellow to orange, sclerotic granules abundant. | Solanum laciniatum |
| 34 | Corollas 2.5 cm or less diam., usually white to pale purple (pale to deep purple in S. umbelliferum); small herbs, subshrubs, or shrubs, to 1.5 m, rarely to 3 m. | > 37 |
| 37 | Corollas pale to deep purple or occasionally white, with green spots edged with white at base of lobes; anthers 3.5–4.5 mm. | Solanum umbelliferum |
| 37 | Corollas white or tinged with purple, often with central star of different color but not with pronounced green spots at base of lobes; anthers 0.7–3.5(–5) mm. | > 38 |
| 38 | Leaf margins deeply and regularly pinnatifid. | Solanum triflorum |
| 38 | Leaf margins entire, or sinuate, sinuate-dentate, to shallowly toothed or lobed. | > 39 |
| 39 | Plants noticeably glandular-pubescent, sticky to the touch. | > 40 |
| 40 | Fruiting calyces not or only slightly accrescent, covering only base of fruit; plants glabrate to moderately pubescent; hairs mostly eglandular but occasionally glandular, to 1 mm. | Solanum nigrum |
| 40 | Fruiting calyces strongly accrescent, covering at least half of fruit; plants moderately to densely pubescent; hairs glandular, 1.5–2 mm. | > 41 |
| 41 | Fruiting calyces covering ca. half of fruit; berries shiny greenish to purplish brown, with (0–)2–3 sclerotic granules; inflorescences usually extra-axillary, 4–8(–10)-flowered. | Solanum nitidibaccatum |
| 41 | Fruiting calyces nearly covering fruit; berries dull pale green, with 4–6 sclerotic granules; inflorescences usually leaf-opposed, 2–5(–7)-flowered. | Solanum sarrachoides |
| 39 | Plants glabrous or eglandular-pubescent (sometimes with a few glandular hairs), not sticky to the touch. | > 42 |
| 42 | Berries yellow, orange, or red when ripe; fruiting pedicels erect; inflorescences leaf-opposed. | > 43 |
| 43 | Shrubs 1–2 m, glabrous or minutely puberulent; corollas 0.7–1 cm diam.; anthers 1.5–2 mm; berries orange when ripe. | Solanum diphyllum |
| 43 | Shrubs to 1 m, glabrous or densely pubescent with branched hairs; corollas 1–1.5(–2.5) cm diam.; anthers 3–4 mm; berries yellow, orange, or red when ripe. | Solanum pseudocapsicum |
| 42 | Berries green, white, yellowish green, or purple to purplish black when ripe; fruiting pedicels erect, spreading, recurved, reflexed, or nodding; inflorescences leaf-opposed or extra-axillary. | > 44 |
| 44 | Inflorescences nearly sessile; berries white to greenish and semitransparent. | Solanum deflexum |
| 44 | Inflorescences 0.5–4 cm; berries green, dark green, yellowish green, or purple to purplish black. | > 45 |
| 45 | Anthers 0.7–1.5 mm. | > 46 |
| 46 | Berries shiny purplish black, with (0–)2–4(–6) sclerotic granules; fruiting pedicels erect or spreading; calyx lobes strongly reflexed in fruit. | Solanum americanum |
| 46 | Berries dull or slightly shiny purple-black, with 6–9 sclerotic granules; fruiting pedicels reflexed or recurved; calyx lobes appressed to spreading in fruit. | Solanum emulans |
| 45 | Anthers (1.8–)2–4.5 mm. | > 47 |
| 47 | Fruiting peduncles sharply reflexed from base. | Solanum chenopodioides |
| 47 | Fruiting peduncles spreading or curved downwards. | > 48 |
| 48 | Berries without sclerotic granules (S. pseudogracile rarely with 2). | > 49 |
| 49 | Fruiting pedicels usually spreading, occasionally recurved; inflorescences racemelike; seeds 1.8–2 × 1.5–1.6 mm. | Solanum nigrum |
| 49 | Fruiting pedicels recurved to reflexed; inflorescences umbel-like; seeds 1–1.3 × 0.8–0.9 mm. | Solanum pseudogracile |
| 48 | Berries with sclerotic granules. | > 50 |
| 50 | Inflorescences forked, 6–14-flowered; w coast from California to Washington. | Solanum furcatum |
| 50 | Inflorescences unbranched, 1–14-flowered; w coast to c and se United States, w, c Canada. | > 51 |
| 51 | Plants decumbent to prostrate, fleshy; sclerotic granules 13–30 per fruit. | Solanum triflorum |
| 51 | Plants erect to sprawling, not fleshy; sclerotic granules 2–13 per fruit. | > 52 |
| 52 | Anthers (2.5–)3–4.5 mm, slightly tapered towards the tips; corollas 1–2 cm diam. | Solanum douglasii |
| 52 | Anthers 1.8–3 mm, not tapered; corollas 0.5–1.5 cm diam. | > 53 |
| 53 | Sclerotic granules 2–4 per fruit; seeds 1.8–2 × 1.5–1.6 mm. | Solanum interius |
| 53 | Sclerotic granules (4–)5–6(–13) per fruit; seeds 1.2–1.5 × 1–1.1 mm. | Solanum nigrescens |