Solanum L. (incl. Lycopersicon Mill.)
Literature: Soria & Heiser (1959), Lawrence (1960), van Ooststroom & Reichgelt (1966), Saarisalo-Taubert* (1967), Edmonds* (1972), Henderson* (1974), Morton (1976), Edmonds* (1977), Heiser & al.* (1979), Schilling* (1981), Symon (1981), Høiland (1983), Lemke (1991), Edmonds & Chweya* (1997), Nee (1999), Shaw (1999), Shaw (2000), Lambinon & al. (2004), Peralta & al. (2008), Stern & al. (2011) (references with an asterisk focus on the Solanum nigrum-complex and/or Solanum section Solanum). Whalen (1984) is particularly helpful for the identification of speciesgroups in subgenus Leptostemonum (the “prickly nightshades”). The results of molecular studies within the New World members of this subgenus were dealt with by Stern & al. (2011).
More information is available on the Solanaceae Source webpages at: http://www.nhm.ac.uk/research-curation/research/projects/solanaceaesource/.
Solanum is a very large, nearly cosmopolitan genus of ca. 1200-1700 species. Its largest species diversity occurs in tropical America. Many species are widely cultivated as vegetables or for medicinal purposes, some also as ornamentals (Lawrence 1960). Only two species (Solanum dulcamara L. and S. nigrum subsp. nigrum) are considered to be native in Belgium, although the latter perhaps rather is an archaeophyte. Lycopersicon was long warranted generic status (mainly based on anther morphology) but is, in fact, nested in Solanum according to several molecular phylogenetic studies (see Peralta & al. 2008 and references therein).
Solanum, especially the S. nigrum-complex, is possibly insufficiently known in Belgium. Some non-native members (S. nodiflorum for instance) might have been overlooked, primarily as agricultural weeds. Solanum scabrum Mill. (syn.: S. melanocerasum All., S. intrusum Soria et Heiser, S. nigrum var. guineense L.) and its putative hybrid with S. villosum (S. xburbankii Bitter) are very reminiscent of S. nigrum subsp. nigrum. The former has been claimed from Belgium (Lambinon & al. 2004) but this requires confirmation. It has brownish anthers (vs. yellow) and larger, purplish berries (ca. 12-17 mm across). Both are sometimes cultivated (garden huckleberries) and might occur as escapes or as sewage aliens (see also Soria & Heiser 1959). Likewise, Solanum melongena L. (eggplant) might occur as a casual on dumps or at sewage works. It has large mauve corollas (30-50 mm across), a dark purplish stem and is usually unarmed.
After drying colour of corollas often change (for instance in several prickly Solanum species) and should therefore be noted in the field.
1. Plant with prickles and/or dendritic or stellate hairs === 2
1. Prickles and stellate or dendritic hairs absent === 8
2. Leaves deeply pinnatifid === 3
2. Leaves entire or shallowly lobed or toothed, never deeply pinnatifid === 4
3. Corolla yellow. Anthers unequal, the 4 uppermost 6-8 mm and straight, the lowermost 10-14 mm and arcuate. Berry ca. 10 mm across, brownish, entirely concealed by the calyx at maturity === Solanum rostratum
3. Corolla white or pale blue. Anthers equal, ca. 10 mm and straight. Berry 15-20 mm across, red, partly exserted at maturity === S. sisymbriifolium
4. Prickles always absent. Hairs dendritic (branched), not stellate. Ripe berry reddish-orange === S. pseudocapsicum (var. diflorum)
4. Prickles always present, although sometimes sparse or almost absent. Hairs stellate. Ripe berry yellowish or reddish-orange === 5
5. Stem and leaves never silvery canescent. Corolla pale violet or white. Prickles stout === 6
6. Leaves with a mixture of stellate and simple, glandular and eglandular hairs, more or less sticky to the touch. Corolla always white, deeply 5-lobed, the lobes reflexed === S. viarum
6. Leaves with stellate hairs only, not sticky to the touch. Corolla pale violet or white, shallowly lobed, the lobes not reflexed === 7
7. Anthers ca. 3-4 mm long. Corolla ca. 15-20 mm across, always white. Spines often narrowly triangular with broad base. Berry often ribbed, at least 20 mm in diameter === S. aethiopicum
7. Anthers 7-9 mm long. Corolla ca. 20-30 mm across, pale violet or white. Spines more slender, slightly broader at base. Berry round, never ribbed, 10-15 mm in diameter === S. carolinense
8. Leaves pinnately lobed or compound === 9
8. Leaves entire to pinnatisect (often 3-lobed in S. dulcamara), never pinnately lobed or compound === 11
9. Corolla usually white or bluish, never yellow. Subterranean tubers present === S. tuberosum
9. Corolla yellow. Subterranean tubers absent === 10
10. Inflorescence usually with less than 12 flowers. Corolla divided ca. 1/3 to ½ to base. Berry usually more than 15 mm across. Plant densely pubescent with longest trichomes up to 3 mm long. Leaflets coarsely dentate, at least at base === S. lycopersicum
10. Inflorescence usually with more than 12 flowers. Corolla divided almost to base (stellate). Berry usually ca. 10 mm across. Plant often less pubescent with longest trichomes up to 1 mm long. Leaflets nearly entire === S. pimpinellifolium
11. Scrambling, perennial vine. Upper leaves 3-lobed. Corolla purple. Inflorescence a multi-flowered panicle (native) === S. dulcamara
11. Annual or perennial, never a vine with lobed leaves. Corolla white or tinged with purple, never entirely purple. Inflorescence a raceme or an umbellate cyme === 12
12. Plant glandular hairy === 13
12. Glandular hairs absent === 16
13. Berries with sclerotic granules (stone cells). Ripe berry green, with conspicuous paler veins. Calyx enlarged in fruit === 14
13. Berries without sclerotic granules. Ripe berry black (rarely green but then without conspicuous paler veins), red or yellow. Calyx not enlarged in fruit === 15
14. Berry entirely concealed by the calyx at maturity, with 4-6 sclerotic granules. Inflorescence usually 3-4-flowered. Plant very sticky to the touch === S. sarachoides
14. Berry only partly concealed by the calyx at maturity, with 2 sclerotic granules. Inflorescence usually 4-8-flowered. Plant not distinctly sticky to the touch === S. physalifolium
15. Ripe berry yellow or red. Inflorescence 3-5-flowered === Solanum villosum p.p.
16. Berry large, 10-15 mm across, green, with numerous large sclerotic granules (ca. 1 mm across). Leaves pinnately lobed, coarsely toothed to nearly entire === S. triflorum
16. Berry smaller, at most 10 mm across. If green, then never with numerous, large sclerotic granules === 17
17. Fruiting peduncle erect, not sharply deflexed. Inflorescence a raceme or an umbellate cyme. Berry black (rarely green), red or yellow. Indumentum sparse === 18
18. Ripe berry yellow or red. Inflorescence 3-5-flowered. Stem usually angular, denticulate-winged === Solanum villosum p.p.
18. Ripe berry black (rarely green or yellow). Inflorescence usually 5-10-flowered. Stem not or only slightly angular === 19
19. Sclerotic granules usually present. Inflorescence an umbellate cyme. Anthers less than 1.5 mm long at anthesis === 20
19. Sclerotic granules always absent. Inflorescence a raceme. Anthers at least 1.5 mm long at anthesis (native) === S. nigrum subsp. nigrum
20. Sclerotic granules six or more. Seedling leaves purplish beneath === S. ptychanthum
20. Sclerotic granules at most five, rarely absent. Seedling leaves green beneath === S. nodiflorum
Additional aliens: Solanum capsicoides All. (syn.: S. aculeatissimum Jacq., S. ciliatum Lam.) (S-Am., vector unknown) and S. pygmaeum Cav. (S-Am., wool,…).
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Henderson R.J.F. (1974) Solanum nigrum L. (Solanaceae) and related species in Australia. Contrib. Queensl. Herb. 16: 1-78.
Høiland K. (1983) Slekta søtvier, Solanum L., i Norge, med vekt på de innførte artene. Blyttia 41: 132-142.
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Nee M. (1999) Synopsis of Solanum in the New World. In: Nee M. & al. (eds.), Solanaceae IV: Advances in Biology and Utilization. Royal Botanic Gardens, Kew: 285-333.
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Symon D.E. & Haegi L.A.R. (1991) Datura (Solanaceae) is a New World genus. In: Hawkes & al. (eds.), Solanaceae III: Taxonomy, chemistry, evolution. Royal Botanic Gardens, Kew: 197-210.
Whalen M.D. (1984) Conspectus of species groups in Solanum subgenus Leptostemonum. Gentes Herb. 12(4): 179-282.