Solanum nigrum L.

Solanum nigrum, the type species of the genus Solanum, is a widespread weed with much morphological variation recognized at various infrageneric levels by many different authors (e.g., Linnaeus 1753; Opiz 1843). There are almost 100 names associated with the taxon, and the status of some of these remains uncertain due to difficulty of finding types but we include them here based on their descriptions (but see Doubtful species). Here, we adopt an inclusive and broad concept of the species and recognise all infraspecific taxa under a single, more widespread and morphologically variable species. Two of the most commonly recognized infraspecific units include S. nigrum subsp. schultesii (Opiz) Wessely (villous, with glandular hairs), and S. nigrum subsp. nigrum (eglandular). Previous studies have found no support for the recognition of these or any other infraspecific taxa within S. nigrum based on morphological (Henderson 1974), seed protein (Edmonds and Glidewell 1977), or molecular marker data (Dehmer 2001; Dehmer and Hammer 2004; Olet 2004; Manoko 2007).

We do not include material identified as S. nigrum in recent African regional floras (Edmonds 2006a, 2006b, 2012) in our circumscription of this species. We follow Olet (2004) and Olet et al. (2011) and consider this material to represent the wild form of S. scabrum. In Africa we consider only material from northern Africa around the Mediterranean and a few specimens (probably introduced from Europe) from South Africa to be true S. nigrum. Both S. nigrum and S. scabrum are hexaploids and morphologically similar, but can be distinguished on the following suite of morphological characteristics; Solanum nigrum has leaves with rather indistinct petioles, inflorescences with the flowers spaced along the rhachis, acute calyx lobes that are more or less appressed to the berry in fruit, berries that are not markedly shiny, and berries that not markedly shiny  and often have stone cells (particularly in Asia). Solanum scabrum has distinctly petiolate leaves, the flowers are usually tightly congested at the tips of inflorescences or inflorescence branches, the calyx lobes are rounded, irregular and strongly reflexed in fruit, and the berries are shiny with thick pericarp and lack stone cells. In addition, the fruiting pedicels of S. nigrum are spreading to somewhat recurved, while those of S. scabrum are erect and strongly spreading.

Throughout its range in Europe and into Eurasia as far as western China, S. nigrum is sympatric with S. villosum. The simplest distinguishing character is mature berry colour; S. villosum has red, orange or yellow berries, while those of S. nigrum are black or green. Many old collections, however, do not state berry colour on the label, so identification can be difficult. Calyx lobes are useful for distinguishing these taxa; S. nigrum calyx lobes are usually deltate and acute, with sharp triangular sinuses, while those of S. villosum are longer, usually rounded at the tip and the sinuses are broad and quite transparent (see description of S. villosum), leaving a paler “window” just below the sinus in flower buds and early flowers. The shiny, translucent berries of S. villosum (mostly slightly ellipsoid) usually dry blackish brown, but are distinct from the matte, more opaque berries of S. nigrum. Neither species has stone cells in Europe, but in Asia, S. nigrum usually has 2 (or occasionally more) stone cells in the berries. Both species retain pedicels after fruits drop, but S. nigrum is not as extreme in this regard and often plants are found with old inflorescences with no remaining pedicels.

Solanum nigrum has been considered native only to Europe, but our study of populations of this widespread weed across its range has shown that largest morphological variation can be observed in Asia. Populations of S. nigrum from Asia have more stone cells in the fruit, and the plants have a more delicate look overall with longer peduncles and often fewer flowers per inflorescence. Material from Asia has been described as different taxa (e.g., S. guanchounense, S. chenopodiifolium) but the variation is continuous across the range, with European populations being more invariant (except in leaf shape and indumentum). Populations in Europe represent a relatively monomorphic set of populations compared to material from China and eastern Asia. We therefore consider that the species is native to the entire Eurasian area, with limited introductions to North America. North American material we have seen appears most similar to European plants based on morphology, suggesting the introduction to North America came from European populations, but this has not been tested genetically.

Australian populations of S. nigrum could have originated either from Europe or from Asia. In general, S. nigrum in Australia does not seem to have stone cells in general, and plants fall into two continuously variable groups: one is similar to classic European S. nigrum, and the other is more similar to plants from eastern and south-eastern Asia.

Solanum nigrum is an autoalloploid species, now thought to have originated from a tetraploid S. villosum and a diploid S. americanum by spontaneous amphiploidy (Edmonds 1979a; Ganapathi and Rao 1986b, 1986c; Poczai and Hyvönen 2011). Cytogenetic and crossing studies show high fertility and regular pairing of bivalents at meiosis in crosses of S. villosum, S. retroflexum, and S. americanum with S. nigrum (Edmonds 1979a; Ganapathi and Rao 1986b, 1986c, 1986d). Of the two tetraploid species, S. villosum and S. nigrum are sympatric at least across parts of their native ranges which would make it more likely that S. nigrum is an autoalloploid derived from the autopolyploid S. villosum and the diploid S. americanum. Molecular analyses have now shown that the two hexaploids S. nigrum and S. scabrum share a parental species with the tetraploid S. villosum (Poczai and Hyvönen 2011). Artificially produced hexaploids from tetraploid crosses of S. villosum and S. americanum have been shown to be fertile and represent the glandular variant of S. nigrum (sometimes recognised as subsp. schultesii (Opiz) Wessely; Edmonds 1979a). It is hence becoming more clear that the tetraploid parent of S. nigrum is S. villosum, and not S. retroflexum. Artificial hexaploids have been produced using S. villosum and S. americanum by several authors and the artificial hexaploids resemble S. nigrum morphologically (Tandon and Rao 1964; Venkateswarlu and Rao 1969, 1972; Soria and Heiser 1959; Edmonds 1979a). Reciprocal backgrossing of the artificial hexaploids with S. nigrum results in high fruit set (Venkateswarlu and Rao 1969, 1972; Edmonds 1979a), supporting the hypothesis that S. villosum and S. americanum are the parent species of S. nigrum. Autoallopolyploid origin of S. nigrum has been suggested by previous authors (Magoon et al. 1962; Rao 1971). In the light of the current molecular evidence combined with the accumulating evidence from cytological and crossing studies, the alternative hypotheses on the origin of S. nigrum as an autohexaploid (Jørgensen 1928; Nakamura 1935, 1937) and an allopolyploid derived from three distinct genomes (e.g., Tandon and Rao 1964, 1966a; Henderson 1974; Edmonds 1979a) are becoming less likely.

In parts of eastern England S. ×procurrens A.C.Leslie (Leslie 1978), a sterile tetraploid hybrid between S. nitidibaccatum and S. nigrum, is locally established where the two species grown together (Stace 2010: 531; Stace et al. 2015). The hybrid has also been recorded in New Zealand (Webb et al. 1988). These plants are intermediate between the two species, with glandular pubescence and black berries with somewhat accrescent calyx lobes. A good description and distribution map for this local hybrid can be found in Stace et al. (2015). We have not seen convincing material from elsewhere in Europe of this hybrid, but it potentially occurs wherever S. nitidibaccatum and S. nigrum co-occur. Because it is sterile, however, it does not spread or persist.

Linnaeus (1753) recognised six varieties of his S. nigrum, of which four are now considered distinct species (var. patulum = S. americanum; var. villosum = S. villosum; var. guineense = S. scabrum; var. virginicum = S. emulans Raf.). Henderson (1974) lectotypified S. nigrum with the single sheet in the Linnean herbarium (LINN 248.28) corresponding to this species. In the protologue Linnaeus (1753) cited several other elements, and it is from these that we select the lectotype for var. vulgare while for var. judiacum he cites no elements. It is possible that a specimen from his herbarium was the basis for this infraspecific epithet, and that the sheet in LINN is that referred to by this name.

In describing S. judaicum, Besser (1809) did not specifically cite Linnaeus’s varietal name, so we have assumed he was coining a new name, rather than making a combination.

The name S. cestrifolium has a complex history; we can find no place of publication of “Solanum cestrifolium Jacq.” as cited by Sprengel (1825) and Weinmann (1824:100; in synonymy with his nomen nudum S. besserianum, see Doubtful names under S. besseri Weinm. ex Roem. & Schult.). The name S. cestrifolium has also been attributed to Willdenow by Gussone (1825, as a nomen nudum) and subsequently validated by Colla (1835); this epithet refers to plants now considered part of the species S. bahamense L. (Strickland-Constable et al. 2008). We have not lectotypified S. cestrifolium Jacq. ex Spreng. in the hopes that material among the cultivated holdings at W will reveal potential original material.

Blume (1826) cited no specimens for any of the names in his Bijdragen tot de flora van Nederlandsch Indië nor do many of the descriptions have specific localities. We have found a specimen labelled S. rhinozerothis in Blume’s hand in L (L.2883159) that we here select as the neotype for that species, but have not found any material directly attributable to Blume that we could associate with S. uliginosum.

The varietal epithet “atriplicifolium” was used by many authors to refer to plants of S. nigrum with dentate leaf margins. It appears to have been used in reference to a specimen that was annotated “Solanum atriplicifolium” by Narcisse Desportes, probably seen in Paris or Geneva. Georg Meyer of Hannover was the first botanist to effectively and validly publish this epithet and did so at the varietal rank. Dunal (1852) cited the same material, and said that the collector was “Prost”, though the G herbarium catalogue states the collector as Desportes. We select this G-DC (G00144334) sheet as the lectotype for S. nigrum var. atriplicifolium because it appears to be original material by way of locality and annotation. The combinations made by Don (1838) and Dunal (1852) are isonyms and therefore have no standing, but we include them here because they have been widely used and cited, and other combinations have been made based upon them.

The various names coined by the amateur Czech botanist Philipp Maximilian Opiz and here recognised as synonyms of S. nigrum were all included by him in the “superspecies” S. nigrum and from descriptions and key represent leaf shape, pubescence and inflorescence size variations of that species. Opiz’s enormous herbarium is housed mostly in PR (Kirschner et al. 2007) with duplicates in PRC and other major European herbaria. We have been unable to visit Prague to examine the no doubt extensive gatherings of S. nigrum, and have found few unambiguous duplicates of the collections cited in the protologues. We therefore leave the typification of these infraspecific names until further study of Opiz’s herbarium can be undertaken. The same is true for the infraspecific names coined by Johann Döll (1843), whose protologues cited some presumed collections, but no herbaria. Searches at KR reveal no original material, and the A. Braun collections cited were probably at B and were destroyed. Again, these infraspecies refer to the highly variable populations of S. nigrum in central Europe. Döll (1843) attributed the infraspecific epithets var. chlorocarpum and stenopetalum to Braun; he was thus coining a new name “chlorocarpum” and not citing Spenner’s earlier use of this epithet.
Solanum chenopodium, S. exarmatum and S. bidentatum were all coined by Rafinesque (1840) for European plants. He cited “S. nigrum var. undatum”, a name never published, in the protologue of S. chenopodium, and suggested that S. bidentatum was the same as “S. patulum of India”. We here place these three in the synonymy of S. nigrum based on their rather meagre descriptions; Rafinesque’s herbarium was destroyed, but occasionally fragments he sent to European herbaria survive (e.g., material relating to S. emulans Raf.)
Dunal (1852) described several varieties of his complex taxon S. pterocaulum (in 1852 written as pterocaulon); most of these correspond to S. scabrum. His var. deppei was described from living material “v.v. Hort. Monsp.”; a sheet in MPU (MPU310704) labelled “Solanum deppei. In hortis bot. cultum” is here selected as neotype for this name.

A single collection of a plant from Nepal cultivated in Avignon was cited in the protologue of S. guineense var. nepalense (Dunal 1852), housed in “h. Requien”. A sheet at AV clearly labelled as “S. guineense β nepalense Prodr.” is most likely original material for the name and we designate this as the lectotype.

Solanum roxburghii was coined by Dunal (1852) as a replacement for “S. rubrum” as used by Roxburgh (1824) in his Flora Indica. Dunal cited the publications of Roxburgh (1824, but with the incorrect page number of 216 rather than 246) and Nees van Esenbeck (1837) and an illustration by Wight, but cited no herbarium material. We consider the illustration in Wight (1843) as the only unambiguous original material for this name, and designate it as the lectotype for S. roxburghii. Both the citations of “Solanum rubrum” are based on the epithet of Miller and/or Linnaeus, and are not at all clear. Differentiating S. nigrum from S. villosum (both which occur in India) can be difficult without ripe berries, and since berry colour in the original hand-coloured illustration at E is green, we are certain the Wight illustration depicts a plant of S. nigrum, with flowers spaced along the inflorescence and sepals that are not reflexed in fruit. We therefore designate an epitype from amongst the sheets collected by Wight (E00718973) to fix application of this name. Early authors such as Roxburgh and Nees van Esenbeck included both red/orange and black-fruited plants in their circumscriptions of both S. nigrum and S. rubrum. The sheets in the East India Company herbarium at K (see de Candolle and Radcliffe-Smith 1981; Noltie 2005) are a complex and confusing mixture of S. americanum and S. villosum; none of these specimens match the illustration as well as does the E sheet we select here as the epitype. This again illustrates the difficulty that early authors had with these very similar plants, and the dangers of assuming that collections are duplicates.

Miquel (1857) recognised several forms of S. nigrum in his broad species circumscription. His forma judiacum was specifically coined to encompass S. judaicum Besser in the sense of Blume (1826), but excluding Besser’s material. We therefore consider this the coining of a new name, and not a new combination based on Besser’s S. judaicum; the lectotype selected is a sheet in L (L2880952) with the locality “in uliginosis circa Buitenzorg” as cited by Blume and in Blume’s hand.

The names coined by the Hungarian botanist Pál Kitaibel were published post-humously by Kanitz (1863) and are largely illegitimate (some were used in earlier publications by Schultes, see discussion under S. villosum). Solanum hirsutum and S. acutifolium were published as alternative names “Solanum hirsutum vel acutifolium” and therefore have the same type; we have selected the sheet in the Kitaibel herbarium at BP with the locality matching that in the protologue (“ex itinere Arvensi”, BP [Herb. Kit. fasc. IX: 103]).
We have selected a specimen collected by Schur (LW00210121), but with a different date of collection and exact locality, as the neotype for S. nigrum var. macrocarpum; searches in the other relevant herbaria revealed no original material.

Edmonds (2012) only lectotypified one of the varieties of S. nigrum from Lowe’s Manual Flora of Madeira (1872). Lowe’s var. hebecaulon cited a single locality and date “Levada de Sta. Luzia, above Funchal, Feb”; no specimens corresponding exactly to that are found in BM or at K.

Solanum probstianum was described from material cultivated in Hungary from seeds sent by Rudolf Probst to Sandor Polgár in 1932. Although no specific specimens were cited in Polgár’s protologue (in Probst 1938), there are many specimens annotated “Solanum probstianum” in Polgar’s hand at BP that are clearly cultivated and appear to be from this original seed collection. We have selected one of these with both flowers and fruits as the lectotype of S. probstianum (BP-272406], it bears a collecting number (4051) and was collected in July 1933. We do not consider the other sheets with this number as necessarily duplicates; the sheets do not have consistent collection numbers, and may represent individual plants from the cultivated population collected on different dates in the same or different years.