The Morelloid Clade, also known as the black nightshades or “Maurella” (Morella), is one of the 10 major clades within the mega-diverse genus Solanum L. The clade is most species rich in the central to southern Andes, but species occur around the tropics and subtropics, some extending well into the temperate zone. Plants of the group are herbaceous or short-lived perennials, with small white or purplish white flowers, and small juicy berries. Due to the complex morphological variation and weedy nature of these plants, coupled with the large number of published synonyms (especially for European taxa), our understanding of species limits and diversity in the Morelloid Clade has lagged behind that of other major groups in Solanum. Here we provide the second in a three-part series of revisions of the morelloid solanums treating the species occurring in North and Central America and the Caribbean (for the Old World see “PhytoKeys 106”, the third part will treat species of South America). Synonymy, morphological descriptions, distribution maps, and common names and uses are provided for all 18 species occurring in this region. We treat 10 of these species as native, and eight as putatively naturalised, introduced and/or invasive in the region. We provide complete descriptions with nomenclatural details, including lecto- and neotypifications, for all species. Keys to all species occurring in the whole region and for each area within it (i.e., North America, Central America and Mexico, and the islands of the Caribbean), illustrations to aid identification both in herbaria and in the field, and distribution maps are provided. Preliminary conservation assessments are provided for all species. Details of all specimens examined are provided in three Supplementary materials sections.

black nightshades, Caribbean, Antilles, Mexico, Central America, North America, Solanum, vegetables, weeds

Solanum L., with approximately 1,400 species, is one of the largest genera of flowering plants (Frodin 2004). The genus poses a taxonomic challenge not only due to its large size, but also due to the 6,931 published names (see solanaceaesource.org), many of which are associated with the cultivated and widespread species of the genus, including the potato (S. tuberosum L.), tomato (S. lycopersicum L.), and eggplant (S. melongena L.). Recent taxonomic and molecular systematic efforts (http://www.solanaceaesource.org) have helped to identify major clades within Solanum (e.g., Weese and Bohs 2007), clarify relationships and the monophyly of previously recognised morphological sections (e.g., Stern et al. 2011), and to provide taxonomic revisions for major clades with keys for species identification (e.g., Knapp 2013).

The Morelloid Clade of Solanum, also known as the Black nightshades or “Maurella” (Morella), is amongst the 10 robustly supported major clades within Solanum (Bohs 2005; Weese and Bohs 2007). This group, which includes the type species of the genus, S. nigrum L., has traditionally been considered difficult, due in part to the weedy nature of its species and its worldwide distribution. The clade comprises 74 currently recognised non-spiny herbaceous and suffrutescent species with simple or branched hairs with or without glandular tips and inflorescences usually arising from the internodes (Särkinen et al. 2015b). Ploidy level varies from diploid to hexaploid within the group (e.g., Edmonds and Chweya 1997; Moyetta et al. 2013; Särkinen et al. 2018; Chiarini et al. 2018), in part contributing to the difficulties in its taxonomy. While taxonomic revisions of the smaller New World sections within the morelloids have recently been published (Del Vitto and Petenatti 1999; Barboza 2003; Barboza and Hunziker 2005), the group in its entirety has not been revised since the 19^th century (Dunal 1852).

General overviews of black nightshade taxonomy have been published (Edmonds 1977, 1978, 1979a), including geographically focused taxonomic treatments for South America (Edmonds 1972), North America (Schilling 1981) and Africa (Edmonds and Chweya 1997; Olet 2004; Manoko 2007; Edmonds 2012) and detailed cytological and morphological studies (Venkateswarlu and Roo 1972; Edmonds 1982, 1983, 1984). Genomic work is being developed with the use of the European S. nigrum as a model system for studying plant/insect interactions (e.g., Schmidt et al. 2004). These studies have greatly enhanced our understanding of the complex morphological and ploidy level variation present in the group, but much taxonomic work remains. A taxonomic treatment of morelloids in the Old World (19 species) has recently been published by Särkinen et al. (2018), including a revision of the nomenclature and typification of the ca. 371 names associated with those species. South America, especially the southern Andes, where more than half of the known species are found (Barboza et al. 2013), is the centre of diversity for morelloids in the Americas. North and Central America and the Caribbean have a distinctly different complement of species to those from continental South America, although some species with wide distributions span the Americas (e.g., S. americanum, S. nigrescens). In addition, several Old World species (e.g., S. nigrum, S. retroflexum) have been introduced or are sporadically cultivated in North America.

Here we provide a taxonomic revision of all 18 native and naturalised (or semi-naturalised) species of the Morelloid Clade occurring in North and Central America and the Caribbean based on a detailed morphological study, including both native and introduced taxa. Some of these taxa have been treated in Särkinen et al. (2018), but we include full descriptions here to aid identification and distributional understanding in the region. One morelloid species from Argentina, S. pilcomayense Morong, has been collected twice in port areas of Texas and New Jersey in the late 19^th and early 20^th centuries probably with ballast or wool waste. It has not been collected again since, so we have not included this taxon in the treatment; a description can be found in Barboza et al. (2013). The work presented here is part of our molecular systematic and taxonomic work focusing on producing a monographic treatment of the Morelloid Clade (e.g., Barboza et al. 2013; Särkinen et al. 2013, 2015a, b, 2018) across its entire range in a series of geographically focussed works, the first of which treated taxa occurring in the Old World (Särkinen et al. 2018) and the last of which will treat the South American species (in preparation).

Knowledge of the European species of black nightshades stretches back to the Greeks and Romans (see summary in Särkinen et al. 2018), and perceptions of the toxicity of these plants among European immigrants to the New World is likely in part to have derived from confusion over the identity of S. nigrum and Atropa bella-donna L., both of which have been referred to as “deadly nightshade”.

Solanum nigrum was the only species of this group treated by Linnaeus (1753). His circumscription was extremely broad and comprised six infraspecific taxa, many of which were based on the plates in Dillenius’s Hortus Elthamensis (Dillenius 1732). He recognised the European S. nigrum (as var. vulgare), S. villosum (as var. villosum), and S. americanum (as var. patulum), included the African cultivated species S. scabrum (as var. guineense), and recognised the native North American S. emulans (as var. virginicum), but he had not seen material of other species treated here (see individual species treatments for details). He clearly recognised all these taxa as very similar and as variants of a worldwide complex; his diagnosis reads “Habitat in Orbis totius, cultis” [Habitat in all the world, cultivated]. He also noted many of these looked like mixtures (“Tot varietates β, γ, δ, ε, ζ videntur esse hybridae proles” [All of the varieties β, γ, δ, ε, ζ seem to be hybrid offspring]). In Species plantarum Linnaeus (1753) did not cite many of the works based on non-European plants (e.g., Piso 1648; Rheede von Draakestein 1689) he had previously cited in Hortus cliffortianus (Linnaeus 1737), and in the Clifford herbarium (BM) specimens of S. nigrum, S. scabrum and S. villosum are preserved, all grown from cultivation.

Miller (1768), in the sixth edition of his Gardener’s dictionary and the first to use Linnaean binomials (see Stearn 1974), described seven members of the Morelloid Clade, five of these as new names (S. villosum Mill., S. luteum Mill., S. rubrum Mill., S. americanum Mill., and S. scabrum Mill.). He did not recognise infraspecific taxa, but also did not indicate he was raising Linnaeus’s varieties to species level. He did not include any new American taxa.

Lamarck (1794) recognised seven taxa, including some not known to either Miller or Linnaeus, such as S. radicans L.f. and S. corymbosum Jacq., both members of the clade belonging to the Radicans group (sensu Särkinen et al. 2015b). He additionally described S. chenopodioides Lam., from material said to be from “île de France” (Mauritius, see species description) and S. triangulare Lam. (= S. americanum) based on an illustration from Rumphius (1750). Some of these early authors re-used epithets (e.g., villosum used by both Miller and Lamarck), but it is not clear whether they were referring to earlier names or not; the principle of priority had not yet become established for botanical naming (see Knapp et al. 2004).

The name for the Morelloid Clade is derived from Dunal’s (1813: 119) un-ranked group “Maurella” that included herbaceous or subherbaceous species with entire leaves. He included 15 species in this group, all of which are still considered members of the Morelloid clade. In his Solanorum synopsis (Dunal 1816) he maintained Maurella, adding to it taxa described by himself and others, most of which are still considered related (except for S. quadrangulare Thunb. = S. africanum Mill., a member of the African Non-Spiny Clade, see Knapp and Vorontsova 2016). Dumortier (1827) used this group, with a changed spelling to “Morella” for the Belgian species. His concept of Morella was narrow and included only those species later recognised as members of Solanum section Solanum: it did not include species now recognised as part of the more broadly defined group (Bohs 2005; Weese and Bohs 2007; Särkinen et al. 2013, 2015b). In the Prodromus Dunal (1852) paid little attention to earlier names and erected an entirely new framework for Solanum mostly composed of gradi ambigui (names of ambiguous rank). Morella, however, was one of the names he continued to use. Within it Dunal (1852) recognised two groups based on inflorescence position, “Morellae spuriae” (6 spp.) and “Morellae verae” (54 spp.). Circumscription of Morella remained obscure and loose during most 19^th and 20^th centuries, with many herbaceous non-spiny taxa treated as members of the group, resulting in the large number of names associated with the Morelloid Clade. Many of these names do not belong to the clade as now recognised based on phylogenetic data (Bohs 2005; Weese and Bohs 2007).

Following the rules on the use of autonyms, Seithe (1962) was the first to name as section Solanum the group containing the type species of the genus (S. nigrum). She also recognised other groups of the Morelloid clade at the sectional level, as sections Campanulisolanum Bitter, Chamaesarachidium Bitter and Episarcophyllum Bitter (all groups confined to South America, see Del Vitto and Petenatti 1999; Barboza 2003; Barboza and Hunziker 2005), now considered part of the larger Morelloid Clade (Särkinen et al. 2015b). Her sectional names were followed by Danert (1967, 1970) with little change. D’Arcy (1972) lectotypified the infrageneric groupings in Solanum and provided an overview of the history of these infrageneric names.

Within the morelloids, four well-supported clades have been recognised based on a detailed molecular phylogenetic study (Särkinen et al. 2015b). These clades loosely correspond to the previously recognised morphological sections: 1) the Radicans clade which comprises four species of Solanum section Parasolanum A.Child (but not including the type species, S. triflorum Nutt.; Bohs 2005), 2) the Episarcophyllum clade that includes most species of Solanum section Episarcophyllum Bitter; 3) the Chamaesarachidium clade that includes two species of Solanum section Chamaesarachidium Bitter; and finally the largest group, 4) the Black nightshade clade, that includes all species of the traditional Solanum section Solanum plus S. triflorum (the first branching species in the black nightshade clade in Särkinen et al. 2015b). The first three clades are restricted to the New World, while most species of the Black nightshade clade occur in the New World but with a secondary centre of diversity in the Old World treated in Särkinen et al. (2018; see Figure 1).

Figure 1. 

Global distribution of the Morelloid Clade of Solanum, showing number of species per 3 degree grid cells (ca. 300 km²) based on native and non-native records.

The Black nightshade clade within the morelloids, also known as the S. nigrum complex and traditionally recognised as Solanum section Solanum, contains many widespread and morphologically variable species; this group has always been considered difficult. Although Edmonds (1972) suggested estimates of species richness had been exaggerated in the group and provided relatively low estimates of species numbers, our ongoing work in the group shows the Black nightshade clade s.s. includes ca. 62 species that are mostly restricted to South America (Särkinen et al. 2015b). Eighteen morelloid species are found in North and Central America and the Caribbean, of which seventeen are black nightshades (incl. S. triflorum) and one (S. corymbosum) is a member of the Radicans group. Eleven of the black nightshades are native (three are endemic to North America north of Mexico, one endemic to Mexico, the rest widespread) and eight are introduced from the Old World or South America (Table 3; Särkinen et al. 2015b). Most of the widespread species in Central America and the Caribbean are shared with northern South America (Colombia, Venezuela and the Guianas). Solanum corymbosum occurs in Mexico widely disjunct from the main species range in Peru and is treated here (Table 3); it is possibly an introduction brought by European explorers from its native range (see Mitchell 2014 and species discussion).

Numerical taxonomic studies have been undertaken in order to resolve species relationships, parental origin of polyploids, and species delimitation in the morelloids (Soria and Heiser 1961; Heiser et al. 1965; Edmonds 1978), but the power of these methods has remained limited due to the complex and often overlapping morphological variation between the closely related species. Species of morelloids show large amounts of morphological variation, especially in growth form, pubescence and leaf morphology. Ongoing phylogenetic work to resolve both relationships and species identity (e.g., Särkinen et al. 2015b) has more promise for untangling these problems.

Floristic treatments of morelloids in North and Central America and the Caribbean in the 19^thand early 20^thcentury (e.g., Gray 1878, Schulz 1909) often treated the native species as S. nigrum or as infraspecific taxa of S. nigrum. Later floristic works (Table 1) treated these taxa in variable ways, but in general citations of S. nigrum as a general term for all morelloids became less common and authors recognised similar numbers of taxa, albeit with variable species epithets (Table 1, see Costa Rica, Guatemala or the state of Illinois as examples; for current distribution of the species treated here see Tables 4 and 5).

Habit and stems. Members of the Morelloid Clade are either herbs or shrubs; species range from annuals (e.g., S. triflorum) to short-lived perennials (e.g., S. douglasii), although some species can develop woody bases and appear to be somewhat shrubby (e.g., S. nigrescens). Stems are usually weak, and occasionally somewhat scrambling, but can reach 2 m in height (Fig. 2A). Plants of all species usually have herbaceous upper stems, even if the base is woody. The stems can be hollow (drying flattened, e.g., S. scabrum) or solid (e.g., S. americanum, S. villosum); this can be a useful character for identification of herbarium specimens.

Figure 2. 

Morphology of the Morelloid Clade of Solanum. A Most species are found in disturbed habitats in the wild (S. douglasii, Ochoterena et al. 979) B small “spinose” processes are common on herbaceous stems in many species of black nightshades (S. emulans, Nee 61357) C glandular hairs are present in some species of morelloids (S. pruinosum, Amith 30248) D small stellate flowers in lateral inflorescences that are developmentally terminal characterise the clade (S. emulans, Nee 61357) E orange-red fleshy berries of S. corymbosum in highly branched inflorescences (Särkinen et al. 4604B) F black fleshy berries of S. nigrum (Nijmegen accession A44750150) G stone cells (also known as sclerotic granules or brachysclerids, L side of photo) are found in the fruits of most species of the Morelloid Clade and are round in shape as compared to the tear-drop shaped or ellipsoid seeds (R side of photo) (the African species S. umalilaense Manoko, Nijmegen accession A24750133) H stone cells are easy to see in herbarium specimens of some taxa (e.g., S. sarrachoides, Blom 2s.n. BM001207745). Photos by S. Knapp, T. Särkinen, and G. van der Weerden (previously published in “PhytoKeys 106”).

Sympodial growth is characteristic of Solanaceae giving the stems a typical “zig-zag” appearance; details of sympodial structure have proved useful for infrageneric classification within Solanum (Child and Lester 1991; Knapp 2002a). Vegetative growth is initially monopodial, but with the onset of flowering, becomes sympodial. The inflorescence is developmentally terminal, and stem continuation is initiated in the axil of the leaf below each inflorescence. Each lateral shoot with alternate leaves arranged in a 1/3 phyllotaxic spiral and a terminal inflorescence is termed a sympodial unit. In some cases, when the axes of sympodial units are fused, the inflorescences appear to originate laterally from the middle of an internode; and when growth of the axes is suppressed, the leaves appear paired (geminate) at a node (Danert 1958). All the members of the Morelloid Clade have difoliate sympodial units with leaves not strongly paired (geminate) at the nodes (Fig. 2C, D), and the inflorescences often arise internodally through axis fusion (Danert 1958, 1967). Occasionally inflorescences appear to be opposite the geminate leaves (e.g., S. sarrachoides) especially on very young shoots (e.g., S. americanum).

“Spinose” processes are common on herbaceous stems in many species of black nightshades (Fig. 2B). They usually occur along the angles of upper parts of larger stems and are often decurrent from leaf bases. These are not true prickles, like those found in the “spiny” solanums (Leptostemonum Clade, see Vorontsova and Knapp 2016) but are similar in that they are outgrowths of the epidermis and are usually associated with trichomes as the enlarged basal portions of stem trichomes that have fallen off. They have been used to differentiate species in this group, but these structures are variable within species where they do occur, and even within stems on a single plant. In addition, they often change markedly in appearance when plants are pressed and dried. Their absence, however, can be diagnostic when combined with other characters.

Leaves. Species of the Morelloid Clade have simple leaves that are generally elliptic or ovate in outline (see Fig. 2 and species descriptions and illustrations). As with other vegetative characters in this group, leaf morphology can be extremely variable within a species or even in a single plant. Many of the infraspecific taxa described for the Eurasian species S. nigrum are based on leaf morphology, particularly in pubescence density and leaf margins.

Leaf margins vary from entire to quite deeply sinuate and lobed. Most populations of S. triflorum have deeply pinnatifid leaves, but a wing of leaf blade is always present along the midrib; some individuals, however, can have almost simple leaves. Other species have variously entire or toothed margins, often the teeth occur only in the basal half to third of the leaf blade. The leaf blade in members of the Morelloid Clade is usually somewhat decurrent on to the petiole and the leaf base is cuneate to attenuate. Leaf apices are acute to attenuate but vary considerably within species.

Petiole length to some extent is related to leaf size, and on individual plants larger leaves always have longer petioles. Solanum scabrum tends to have long petioles with little decurrent leaf blade tissue; this character can be helpful in distinguishing it from the otherwise very similar S. nigrum.

Pubescence. Trichomes in species of the Morelloid Clade are simple or branched (e.g., S. pallidum Rusby of the Andes), but never stellate (Seithe 1962; Roe 1971). The species treated here have only simple trichomes; these are usually 1–6-celled and uniseriate. Occasionally the trichome base is enlarged with the lowermost cell much larger than more distal cells and these enlarged bases persist as “pseudospines” on stems (see above, Fig. 2B). Much importance has been placed on differences in density of pubescence as a taxonomic character (e.g., the densely pubescent plants of S. nigrum sometimes recognised infraspecifically as var. or subsp. schultesii in European floras), but pubescence within taxa is continuously variable and apparently also related to environment, with plants growing in sunny sites often recorded on labels as more densely pubescent.

The presence or absence of glandular trichomes has also been previously treated as taxonomically significant (see Edmonds 1972, 1979b, 1982), with glandular and eglandular morphotypes being treated as separate subspecies or varieties (see Edmonds 2012). Manoko (2007; Manoko et al. 2008) showed that this character did not correspond to coherent groups in AFLP analyses of S. nigrum or S. villosum. Seithe (1962, 1979) showed that in most Solanum species glandular trichomes are found on cotyledons and hypocotyls of seedlings and are lost as plants mature; she suggested that species with glandular trichomes were more “primitive”. It is equally probable that the retention of glandular tips on trichomes is a simple paedomorphic character and that it has little taxonomic significance if not correlated with other characteristics. Some species treated here are only occasionally glandular (e.g., S. triflorum), with the glandular trichomes very small and sparse; in these plants eglandular trichomes dominate. Solanum pruinosum consistently possesses glandular trichomes (Fig. 2C) that are spreading and translucent, unlike the more appressed, white-coloured trichomes found in other taxa such as S. nigrescens.

Modern developmental work has not been undertaken with morelloid trichomes, but work has been done with the glandular trichomes of tomatoes and their relatives (e.g., Bergau et al. 2015). These studies suggest that these trichomes play a role in pest defence through release of metabolites in response to insect contact. Local ecological and herbivore pressures may also play a role in the presence or absence of glandular trichomes in the morelloids; this may help explain the highly heterogeneous distributions of glandular and eglandular individuals in some morelloid species.

Inflorescences. The inflorescence of members of the Morelloid Clade is developmentally terminal and later overtopped by the leading axillary shoot so that it appears lateral (Fig. 2D); this is common to many clades of the genus (an exception is the Pteroidea clade with axillary inflorescences, Knapp and Helgason 1997; Tepe and Bohs 2010). The basic structure is a scorpioid cyme that is unbranched or variously branched. Most members of the black nightshades have unbranched (simple) or merely forked (once-branched or furcate) inflorescences, but S. corymbosum has inflorescences that consistently branch more than once (Fig. 2E). The degree of branching in some species of the group may also depend upon plant or inflorescence age (e.g., S. pseudogracile). In all Solanum species the inflorescence expands from the tip producing flowers in a proliferating manner (Lippmann et al. 2008).

All members of the group have distinct peduncles, usually somewhat longer than the distal flower-bearing portion, but inflorescence length and flower number vary both between and within species. Many species in the group have what are termed “sub-umbellate” inflorescences, where the flower-bearing rhachis is very short and the pedicels are all very closely spaced and congested at the very tip of the inflorescence. We use the term sub-umbelliform in the species descriptions for this flower clustering (see Fig. 2D). This inflorescence is not a true umbel, but is described as such in much previous literature, usually as an umbellate or subumbellate cyme (e.g., Edmonds and Chewya 1997; Edmonds 2012). Both peduncles and pedicels usually have pubescence that is similar to that of the stems and leaves, or somewhat reduced distally. The peduncles of S. chenopodioides are unique in being strongly deflexed, creating a right or acutely downward facing angle with the stem (Fig. 7D).

Pedicels in flower are usually deflexed or spreading, but this can be very difficult to see in herbarium specimens. In fruit, pedicels are usually somewhat pendent from the weight of the berry, but are strongly (e.g., S. chenopodioides, S. macrotonum) or weakly (e.g., S. nigrescens) deflexed in some species. Other species have markedly spreading pedicels in fruit (e.g., S. americanum). The abscission zone at the pedicel base in members of the Morelloid Clade is at the very base, and if and when pedicels fall, the scars are generally flush with the rhachis. In S. interius the basal flower in the inflorescence has the pedicel articulation markedly above the base; this can be a useful identification character. Pedicel persistence with fruit ripening is an important species character in this group. Ripe berries either fall or are taken from the plant with the pedicel still attached (e.g., S. emulans, S. nigrescens) or the berry falls alone, and the pedicel is left behind (e.g., S. americanum, S. villosum). The presence of old pedicels can be useful for identification of non-flowering herbarium specimens.

Calyces. The calyx in all members of the Morelloid Clade is 5-merous and synsepalous. The calyx tube is generally conical or occasionally somewhat elongate (e.g., S. corymbosum), and the lobes are extremely variable in size and shape ranging from deltate and rounded (e.g., S. americanum) to long-triangular (e.g., S. emulans). The position of the calyx lobes in fruit is an important identification character; they can be strongly reflexed (e.g., S. americanum), spreading (e.g., S. emulans, S. nigrescens) or appressed to the berry (e.g., S. corymbosum, S. douglasii). The calyces of the weedy introduced species S. nitidibaccatum and S. sarrachoides are accrescent in fruit with the calyx lobes expanding to envelope almost the entire berry (several South American members of the group also have accrescent calyces; see Särkinen and Knapp 2016).

Corollas. In common with most species of Solanum, members of the Morelloid Clade have 5-merous sympetalous corollas that are variously stellate. Fasciated floral mutants are often observed, where 4–6-merous corollas can occur on individual plants that are otherwise 5-merous (e.g., S. scabrum). Colour is generally white or pale violet-tinged in the species treated here, but anthocyanin pigmentation can vary depending on environmental growth conditions. In most species at least some individuals (collections) with purple and violet flowers have been recorded (a single South American species of the group has pale yellow flowers S. huayavillense Del Vitto & Peten.; all of the species treated here have white or pale purple flowers). At the base of the corolla tube there is usually a ring or irregular area of differently coloured tissue usually referred to as the “eye”; in the species of the Morelloid clade this is usually yellow or greenish yellow. This eye is usually similar in texture to the rest of the corolla and not shiny as occurs in the Dulcamaroid Clade (see Knapp 2013); in some species the eye has darker brown or blackish purple margins (e.g., S. nitidibaccatum). The colours of the eye usually disappear in herbarium specimens and are rarely noted on labels.

Corollas in the Morelloid Clade are stellate, deeply stellate or rotate-stellate, and corolla lobes are deltate to long-triangular. Solanum triflorum has deeply stellate corollas, with narrow, reflexed corolla lobes, whereas S. corymbosum has corollas with the lobes approximately the same length as the tubular portion, and the lobes are not strongly reflexed at anthesis. These characters, particularly those of the degree to which corolla lobes are reflexed, can be very difficult to see in herbarium specimens. As is seen in many other groups of solanums (e.g., Dulcamaroid Clade, African Non-Spiny Clade, see Knapp 2013; Knapp and Vorontsova 2016) where flowers last more than one day, the corolla lobes can be more or less reflexed through the life of the flower. Lobes are often spreading on day one, become reflexed to strongly reflexed on subsequent days, and as the flower ages, become spreading again.

Corollas of members of the Morelloid Clade are usually very small, as compared to other groups of Solanum species; these species have among the tiniest flowers of any Solanum. Corolla diameter varies from 4–20 mm; S. nitidibaccatum has the smallest corollas and S. douglasii the largest. Adaxial lobe surfaces are usually glabrous, while abaxial corolla lobe surfaces are variously papillate, with longer simple uniseriate trichomes on the margins and tips.

Androecium. The stamens of members of the Morelloid Clade are ellipsoid-anthered and equal to very slightly unequal in size and length. The filament tube and filaments are variously pubescent adaxially. The trichomes on filaments are simple and uniseriate; they are usually weak-walled and tangled. The filament tube is generally very short to almost absent and the free portion of the filaments is distinct. Filament length in comparison to anther length is a useful character for distinguishing species. In most species of morelloids the free portion of the filament is more or less equal to the anther length, but in some species pairs with otherwise similar anther length (e.g., S. americanum, S. emulans) differences in free filament length can be diagnostic (S. emulans has much longer filaments than does S. americanum). Solanum douglasii and S. nigrescens are similar in overall stamen length, but S. douglasii has very short filaments and longer anthers, while the filaments and anthers of S. nigrescens are more equal in size. The length of filaments can affect the biophysical properties of anther vibration and thus vibratile pollination (e.g., Timerman et al. 2014; Switzer and Combes 2016), and may be an important characteristic involved in speciation in this group.

Anthers of members of the Morelloid Clade conform to the poricidal morphology of all other species of Solanum (see Knapp 2001). In common with other “non-spiny” solanums, the anther is ellipsoid and the terminal pore usually “unzips” during anthesis to become an elongate slit. The anthers are loosely connivent, and not connected by either “glue” (as in S. dulcamara, see Glover et al. 2004) or elongate papillae (as in the tomatoes, see Peralta et al. 2008). Anther size is an important identification feature in the Morelloid Clade, varying from less than 1 mm (S. americanum, S. emulans) to ca. 4 mm long (S. douglasii); in such small flowers, small differences can be very important. Pollen is not useful in distinguishing members of this group (Edmonds 1984).

Gynoecium. The gynoecium in members of the Morelloid Clade is bicarpellate; the carpels are fused in a superior ovary with axile placentation. The ovary is glabrous, and usually conical to globose. The flowers lack nectaries, as do all species of Solanum. The style is straight or slightly curved and usually sparsely to densely pubescent in the lower half to third where it is enclosed in the anther cone. It is usually exserted from the anther cone, but in some species (e.g., most populations of S. americanum, S. corymbosum) only barely exceeds the length of the stamens. This may be related to self-fertilisation and thus self-compatibility, as has been observed in the tomatoes (Rick et al. 1977, 1978, 1979; Rick and Tanksley 1981; Peralta et al. 2008), but all species of the Morelloid Clade tested have been self-compatible (Edmonds 1979a; Schilling and Heiser 1979; Eijlander and Stiekema 1994; Olet 2004). None of the species of the Morelloid Clade treated here has heterostylous flowers. The stigma is either very minutely capitate (e.g., S. nigrescens) or larger and more obviously globose-capitate (e.g., S. douglasii, S. emulans). The ovules are anatropous and non-arillate.

Fruits. As with all species of Solanum, the fruit is a bicarpellate berry. Fruits of members of the Morelloid Clade are usually brightly coloured and juicy (Fig. 2E, F). Most species have globose berries, but those of the introduced species S. villosum are usually somewhat longer than wide. Berry colour is usually green, yellowish green (e.g. S. triflorum) or varying shades of purple and purple-black (many species); immature berries are usually described as green on herbarium labels. Solanum villosum has bright orange or yellow translucent berries and S. corymbosum has orange to red berries that are opaque (Fig. 2E). Colour polymorphisms are common in species of this group in the Old World; both S. nigrum and S. tarderemotum Bitter, for example, have individuals and populations with green or purple berries. Manoko (2007) showed that berry colour did not differentiate groups within European populations of S. nigrum. Despite this variation, berry colour is an important identification aid in this group, but is often not recorded on herbarium labels, especially of older specimens.

The pericarp (epicarp) of the berries is thin and either matte (e.g., S. chenopodioides, S. emulans) or shiny (e.g., S. americanum, S. pseudogracile). Surface characteristics are useful for species identification, especially when combined with other characters (see discussion of S. americanum). The mesocarp is always juicy and very liquid; these fruits are eaten by both birds and mammals (including people). In general, the mesocarp of fresh fruits is green or greenish yellow, but in species with purple berries it is sometimes purplish. Berries of some species are markedly translucent (e.g., S. villosum, Fig. 55E), while most species are opaque (e.g., S. nigrum, Fig. 2F, S. interius, Fig. 22D). Neither of these characters is usually mentioned on herbarium labels.

Like some other groups of non-spiny solanums such as the Pachystemonum (Cyphomandra) Clade (Bohs 1998) and the Archaesolanum Clade (Symon 1994) berries of members of the Morelloid Clade contain small, hard inclusions commonly referred to as sclerotic granules, stone cells or brachysclereids (Bitter 1911, 1914; in species descriptions here referred to as stone cells). These concretions are composed of modified sclerenchyma cells with massively enlarged cell walls (Fig. 2G, H); the stone cells of pears and quinces (Rosaceae) are classic examples of this cell type. Neither their function nor their origin in Solanaceae is known. Bitter (1914) suggested that they existed in an evolutionary series in the family, with more “advanced” taxa lacking them altogether (e.g., the spiny solanums). Some members of the Archaesolanum Clade have more stone cells than seeds in each berry (e.g., S. aviculare G.Forst. with an average of 12–55 seeds and 491–607 stone cells, Symon 1994). In the Morelloid Clade these stone cells are usually quite small and are always round in shape, ca. 0.5 mm in diameter, and brown to white in colour (Fig. 2G, L hand side of photograph). Stone cells can usually be easily seen in dried specimens without dissecting the berry (see fig. 1 in Bitter 1914; Fig. 2H); they appear globose and are often larger than the seeds. Sometimes stone cells of different sizes are found in the same berry, but this character is not consistent within species. The number of these is usually relatively consistent within a species, and varies from absent (e.g., S. chenopodioides, S. retroflexum, S. scabrum, S. villosum) to (1)2–4(–6) (e.g., S. interius, S. macrotonum, S. nigrescens) to more than 10 (e.g., S. furcatum, S. triflorum). Solanum americanum varies from 0 to 4 stone cells per berry. Bitter (1914) reported that in crosses involving morelloid species with and without stone cells hybrids had stone cells present in the fruit, indicating that this was an inherited character. Cultivated species (e.g., S. scabrum, S. villosum) tend to lack stone cells; this may be related to human-mediated selection.

Seeds. Members of the Morelloid Clade have flattened seeds, like many other solanums. Unlike other groups, however, they are usually tear-drop rather than kidney shaped, with the hilum and micropyle at one of the short ends of the seed (see Fig. 2G, R hand side of photograph). Seed size varies from 1–3 mm long, and in general polyploid species have larger seeds than diploids (e.g., S. americanum seed size is 1–1.5 mm, while that of S. scabrum is 2–2.8 mm). Solanum interius, however, has very large seeds (1.8–2 mm) and is diploid. Seed size is a good feature for distinguishing S. nigrum (hexaploid) from S. americanum (diploid). Seed number per berry in the Morelloid Clade is generally quite high (Särkinen et al. 2015b), with usually 30–50 seeds in each berry.

Seed coat morphology has been suggested as a useful character for species-level taxonomy in Solanum (Souèges 1907; Lester and Durrands 1984) and has been useful in delimiting groups in some clades (e.g., Geminata Clade, Knapp 2002a). All of the species treated here have sinuate-walled (digitate) testal cells. The lateral walls of these cells of the outer epidermal layer develop lignified radial thickenings that form as hair-like structures (Souèges 1907; Lester and Durrands 1984; Axelius 1992; Peralta et al. 2008). When the outer wall of the epidermis is removed, either naturally (e.g., by passage through frugivore guts; see Barnea et al. 1990) or by enzymatic digestion (Lester and Durrands 1984; Knapp 2002a) the seeds appear pubescent; seed measurements here include these projections. Edmonds (1983) examined seed coat patterns in some members of the Morelloid Clade (species previously included in Solanum section Solanum) and found no useful variation for delimiting either species or species groups.

Chromosomes. Chromosome numbers in the Morelloid Clade are variations on the base number of 12 (Table 2). The chromosomes are very small; an unvouchered diploid accession grown in India (Bhiravamurty 1975) had median, submedian and subterminal centromeres indicating variation in chromosome morphology. The Morelloid Clade, along with the potatoes, is one of the few lineages in Solanum where polyploidy is common (see discussion of polyploidy and hybridisation in Särkinen et al. 2018; Chiarini et al. 2018). Polyploidy is common in the Old World members of the group (Särkinen et al. 2015b, 2018), but less so for New World taxa (although many South American species have not had chromosome counts). Variation in ploidy level within a species is not common in Solanum, but S. macrotonum appears to have diploid (Central and South America) and hexaploid (South America) populations and similar variation occurs elsewhere in both morelloids (e.g., S. interandinum Bitter of the northern Andes) and in the potatoes (see Spooner et al. 2014). DNA amounts in unreplicated gametic nuclei (C-values) vary between 1.03 pg in S. americanum (as S. nodiflorum) and 3.10 pg in S. nigrum (Bennett and Leitch 2012).

Many chromosome counts have been reported for members of this group, often as unvouchered counts of “Solanum nigrum”. In the species treatments we only report counts that are based on identifiable material or those that are vouchered and for which we have verified the specimen in question. Chromosome counts recorded in floras (e.g., Radford et al. 1964) without vouchers are not listed.

Habitats and distribution. Members of the Morelloid Clade are plants of disturbed habitats and occur in landslides, along roads and streams, and at the edges of cultivated fields (Fig. 2A). Many of the species have broad elevational ranges (e.g., S. americanum) and extremely broad distributions (see Tables 3, 4 and 5). Species diversity in the region treated here is highest in North America (Canada and the United States; Table 3), with 7 native and 8 adventive species. This is largely due to the high numbers of adventive species occurring in the temperate parts of the continent as weeds of agriculture or escapes from cultivation, but S. emulans and S. pseudogracile are endemic to North America. The southeastern states of the United States have the highest species diversity on the North American continent (see Table 5). Central America and the Caribbean share three extremely common and widespread species (S. americanum, S. macrotonum and S. nigrescens); these also occur in Mexico and south to northern South America.

Adventive species from Europe such as S. nigrum and S. villosum are often recorded as growing on ballast near ports. Solanum pilcomayense (not treated here, see Introduction) of the Río Paraná drainage (Argentina, Paraguay, Brazil) has been recorded only twice, once in New Jersey and once in Texas, both times in the 19^th century; unlike S. nigrum and S. villosum however, it has not spread further, nor has it been collected recently. It must not be assumed, however, that only adventive non-natives occur on ballast, many collections of S. emulans have also been made on such disturbed sites along the eastern seaboard of the United States.

Several members of the group (e.g., S. nigrum, S. nigrescens, S. nitidibaccatum) are registered as noxious weeds of agriculture (see below) in both Europe and North America (Arnold 1985; Burgert et al. 1973; Ogg et al. 1981; Rogers and Ogg 1981; Defelice 2003; Orgeron et al. 2018). Solanum triflorum is listed as a declared weed in Tasmania (Weed Management Act 1999 2000). Confusion over the identification of individual species (Ogg et al. 1981) and the common use of “S. nigrum agg.” in describing these species makes assessment of their invasive status very difficult in the absence of vouchers. Most morelloid species are weedy in nature.

We list the status and general distribution of the species in the group in Table 3, and in Table 4 document country distribution from herbarium specimens (see Materials and methods).

Pollination and dispersal. Like all solanums, flowers of members of the Morelloid Clade are buzz-pollinated by bees (Buchmann et al. 1977; De Luca and Vallejo-Marín 2013). Females of solitary bees and bumblebees vibrate the anthers with their indirect flight muscles causing pollen to “squirt” out of the terminal pores; they curl their bodies over the anther cone and rotate around the flower (Buchmann et al. 1977). The pollen is then groomed from the body and packed into the corbiculae, but the area of the venter that contacts the stigma of the next flower cannot be reached. Smaller bees visit and buzz individual anthers (Symon 1979), but do not usually contact the stigma and thus in solanums with large flowers are more properly seen as pollen thieves. Some bees also exhibit “milking” behaviour, where insects grasp the lower part of the anthers and try to force pollen out of the apical pores using upwards pressure (Buchmann et al. 1977). “Gleaning” of loose pollen grains is also done by various small bees and flies (Symon 1979; Knapp 1986). Buchmann et al. (1977) studied S. douglasii where flowers were visited and buzzed by a wide range of bees in various families, but no more recent pollination studies have been carried out. Few pollination studies have been carried out on the morelloid species.

Members of the Morelloid Clade have juicy berries with thin pericarp (skins) that are typical for bird-dispersed fruits (Knapp 2002b). Studies of dispersal of morelloid species have mostly been done on the species occurring in the USA with native bird and mammal frugivores (quail, American robins and deer mice; Tamboia et al. 1996). Green fruits are expected to be more attractive to mammals but Tamboia et al. (1996) found that both birds and mammals preferred the purple berries of S. americanum to the green berries of S. sarrachoides (probably = S. nitidibaccatum, no vouchers cited). The suite of characters expected to be attractive to mammals such as green colour, odour, and abscission shortly after ripening are all found in some of the morelloids, suggesting that mammals may be important fruit dispersers for these plants as well as birds.

Glycoalkaloid concentrations are very low in ripe berries of S. americanum and other members of the Morelloid Clade that have been tested, and alkaloid levels are similar across the clade (Cipollini et al. 2002). Higher concentrations in unripe fruit (Cipollini et al. 2002) of these species make them unattractive to frugivores (Cipollini and Levey 1997a). This loss of secondary metabolites in ripe berries is common across Solanum species with brightly coloured, fleshy fruits (e.g., Bradley et al. 1979) and is most likely related to fruit persistence (Cipollini and Levey 1997b), where risk of fungal infection is balanced by probability of animal ingestion and thus dispersal. Glycoalkaloids are known to have a constipative effect (see above, e.g., Gerard 1597) and to inhibit seed germination after ingestion (Cipollini and Levey 1997b), but Wahaj et al. (1998) found that ripe berries of S. americanum had a laxative effect on birds thus speeding seed passage through the gut. They suggested this was due to some other chemical compound (perhaps calystegines (?), see Dräger et al. 1994). Bravo et al. (2014), however, found that ingestion of seeds of S. nigrum by great bustards (Otis tarda) reduced seedling emergence, but suggested that because seed numbers were so high, the bustrads still functioned as efficient seed dispersers.

Conservation status. Most morelloid species are weedy and widely distributed; in the Old World many species are also cultivated (e.g., S. scabrum, S. tarderemotum, S. villosum) and are distributed widely via human migration. Many introductions of species from Europe particularly to North America may have resulted from transport of soil or seed with introduced crops, but even casual visitors to far-flung places have been implicated in the introduction of alien species (Chown et al. 2012). It is likely that the early explorations of the southern hemisphere inadvertently carried seeds of nightshades with them, accounting for the widespread nature of many of these taxa. The genetic structure of populations of extremely widespread species such as S. americanum will need to be investigated to determine if structure exists in the distribution that can be related to natural or human-mediated causes.

Preliminary conservation assessments for the Caribbean and North and Central American members of the Morelloid Clade (including introduced taxa) are presented in Table 6. All of these species can be assigned the status of Least Concern; Table 6 records only the Extent of Occurrence (EOO), because Area of Occurrence (AOO) is highly influenced by collection or georeferencing deficit.

Black nightshades are used as potherbs (often referred to on English language labels as “spinach”) worldwide, especially in Africa. In the Americas, these plants are used in similar ways, especially among communities of African origin, but also more widely. It is not clear whether the use of leaves of morelloid solanums was brought to the Americas by enslaved peoples from Africa; it is more likely their use as potherbs developed in parallel indigenously on both continents.

Moerman (1998) records medicinal, culinary and other uses for several morelloid species amongst native peoples of North America. Some of these are identifiable to species (i.e., S. douglasii, S. nitidibaccatum, S. triflorum) but a great many uses are attributed to “Solanum nigrum”. Use of these plants to relieve loneliness due to death of family members among people of the Cherokee Nation living in the Smoky Mountains in North Carolina (Banks 2004) is likely to refer to S. emulans, as is the use of “S. nigrum” as “the best relished” potherb by the Cherokee in northwestern Georgia (Witthoft 1947). Ceremonial use in medicine ceremonies by the Objiwa (Chippewa)in Minnesota (Reagan 1928, quoted in Moerman 1998) certainly refers to S. emulans. The use of ripe berries as food by several peoples of coastal and central California (Tübatulabal, Ohlone, Mendocino) is likely to refer to S. douglasii, and the smoking of leaves to relieve toothache and as a remedy for scarlet fever among the Ohlone (as Costanoan) recorded by Harrington (Bocke 1984) also probably is attributable to S. douglasii (with the recorded common name of chichiquelite, taken from the Spanish). The Houma people of Louisiana’s use of a morelloid to treat worms in children could apply to S. americanum, S. nigrescens or S. pseudogracile. Where uses of these species are clearly of a single taxon (e.g., S. douglasii, S. nitidibaccatum, S. triflorum from Moerman 1998) or are vouchered they are recorded in the species treatments.

Many common names for these taxa in Mexico (see species treatments) include the suffix “-quelite” which is a generic term for potherbs. In the United States of America, the berries are eaten in pies and jams, but leaves appear not to be used as widely as they are further south (but see above and species treatments). Many manuals or floras list black nightshade berries as toxic (e.g., Kingsbury 1964), but see Särkinen et al. (2018) for a discussion of this in relation to plant chemistry.

Our goal for the treatment of the Morelloid Clade has been to provide circumscriptions for the members of this morphologically variable group of species, while clearly highlighting areas, taxa and populations where further in-depth research would be useful. Delimitation of species here basically follows what is known as the “morphological cluster” species concept (Mallet 1995): i.e., “assemblages of individuals with morphological features in common and separate from other such assemblages by correlated morphological discontinuities in a number of features” (Davis and Heywood 1963). Biological (Mayr 1982), phylogenetic (Cracraft 1989) and the host of other finely defined species concepts (see Mallet 1995) are almost impossible to apply in practice and are therefore of little utility in a practical sense (see Knapp 2008a). It is important, however, to clearly state the criteria for the delimitation of species, rather than dogmatically follow particular ideological lines (see Luckow 1995; Davis 1997). Our decisions relied on clear morphological discontinuities to define the easily distinguished species. Specific characters used for recognition are detailed with each species description and in the key. Some potential reasons for variability and intergradation are recent divergence, hybridization and environmental influence on morphology. In this revision we have tried to emphasise similarities between populations instead of differences, which so often reflect incomplete collecting or local variation. We have not recognised subspecies or varieties, but have rather described and documented variation where present, rather than formalised such variability with a name which then encumbers the literature. We have been conservative in our approach, recognising as distinct entities those population systems (sets of specimens) that differ in several morphological characteristics. Many of the species in the group (and of morelloids in general) are extremely widespread and variable; variation exists in certain characters, but the pattern of variation is such that no reliable units can be consistently extracted, nor is geography a completely reliable predictor of character states. Here variability within and between populations seems more important than the variations of the extremes other taxonomists have recognised as distinct. We describe this variation realising that others may wish to interpret it differently.

Although infraspecific taxa have been recognised by others within the group, we do not recognise any here due to the complex morphological variation observed within each species, where the inspection of large number of specimens quickly reveals no apparent natural breaks in variation but rather a mixing between highly morphologically variable populations of widespread species.

Our taxonomic treatment is based on results from recent molecular systematic studies considering the taxonomy of the section and the molecular phylogenetic study of the entire Morelloid Clade by Särkinen et al. (2015b). Descriptions are based on field work and examination (physical and virtual) of 20,370 [=16,004 collections] herbarium specimens (of which 13,111 were from the New World) from 228 herbaria (A, AD, AK, ALCB, ANG, APSC, ARIZ, ASE, ASU, AZU, B, B-W, BA, BAH, BBLM, BH, BHCB, BHSC, BLMV, BM, BOIS, BP, BR, BRI, BRU, BRY, BSD, BSHC, BUT, C, CAL, CANB, CAS, CEN, CEPEC, CESJ, CGE, CHR, CICY, CLEMS, CM, CNS, COI, COL, COLO, CONN, CORD, CPUN, CR, CRMO, DBG, DD, DES, DNA, DS, DSC, DSM, DUKE, DVPR, E, EA, EAC, ECON, EIU, EKY, EMS, ESA, EWU, F, FCQ, FSU, FT, FUEL, FURB, G, G-DC, GA, GAS, GB, GH, GMUF, GOET, H, HAJB, HAMAB, HAO, HAS, HBG, HO, HOXA, HST, HUCS, HUEFS, HUEM, HUSA, HUT, IAC, ICN, ID, IDS, IFP, ILLS, INB, IND, INPA, IPA, JE, JEPS, JOI, JPB, K, KFTA, KHD, KIRI, KUFS, L, LAGU, LE, LEA, LIL, LL, LOJA, LP, LPB, LSU, LU, M, MA, MAC, MARY, MBM, MBML, MEL, MERL, MEXU, MHES, MHU, MICH, MIN, MISS, MISSA, MO, MOL, MONT, MONTU, MOR, MPU, MPUC, MT, MU, MY, NCU, NE, NEBC, NSW, NY, OBI, OS, OSC, OTA, OUPR, OXF, P, P-LA, PACA, PAL, PBL, PERTH, PH, PNNL, POM, PSM, Q, QAP, QCNE, RAB, RENO, RM, RSA, S, SASK, SD, SGO, SI, SJRP, SMDB, SOC, SRSC, TAN, TEX, TO, U, UB, UBC, UC, UCR, UDBC, UEC, UFP, UFRN, UMO, UNCC, UOS, UPCB, UPS, URV, US, USF, USM, USMS, UT, UTC, V, VEN, VIES, VPI, VT, W, WAG, WCW, WELT, WIS, WOLL, WTU, WU, WWB, YU, Z). Some of these specimens (especially for North America) were examined digitally through the portals of SEINet (http://swbiodiversity.org/seinet/index.php), the Southeast Regional Network of Expertise and Collections (SERNEC, http://sernecportal.org/portal/index.php), the Consortium of Northeast Herbaria (www.cnh.org), the Consortium of Midwest Herbaria (www.midwestherbaria.org), and the Consortium of Pacific Northwest Herbaria (http://www.pnwherbaria.org/); we include only those specimens we have been able to unequivocally identify from these images or that are duplicates of collections we have personally examined. We have compared introduced and adventive species across their entire ranges, not only collections from North and Central America and the Caribbean.

Measurements were made from dried herbarium material supplemented by measurements and observations from living material. Colours of corollas, fruits, etc., are described from living material or from herbarium label data. Specimens with latitude and longitude data on the labels were mapped directly. Some species had few or no georeferenced collections; in these cases, we retrospectively georeferenced the collections using available locality data. Maps were constructed with the points in the centres of degree squares in a 1° square grid. Conservation threat status was assessed following the IUCN Red List Categories and Criteria (IUCN 2017) using the GIS-based method of Moat (2007) as implemented in the online assessment tools in GeoCat (http://geocat.kew.org). The Extent of Occurrence (EOO) measures the range of the species, and the Area of Occupancy (AOO) represents the number of occupied points within that range based on the default grid size of 2 km². We present only the EOO in the threat assessments for widespread species; AOO is very sensitive to georeferencing bias and collecting effort.

Type specimens for many morelloids have proved difficult to trace; most of the names for the introduced European species (e.g., S. nigrum, S. villosum) and for North and Central American species introduced elsewhere (e.g., S. americanum, S. triflorum) have been treated in Särkinen et al. (2018). Decisions on choices of lectotypes and synonymy can be found there.

Where specific herbaria have not been cited in protologues we have followed McNeill (2014) and designated lectotypes rather than assuming holotypes exist. We cite page numbers for all previous lectotypifications. In general, we have lectotypified names with the best preserved, or in some cases with the only, herbarium sheet we have seen; in these cases, we have not outlined our reasoning for the lectotypifications. Where there has been difficulty or where the choice may not be obvious, we detail our reasoning at the end of the species discussions (e.g., see Smith and Figueiredo 2011).

Georg Bitter described many taxa of Solanum in the course of his monumental work on the genus Solanum and worked widely in Germany in the period between the two World Wars (Weber 1928), including, but not exclusively at Berlin. His protologues frequently include specific herbarium citations, but often do not. We have cited specimens as holotypes only when a single specimen with a single herbarium citation is indicated in the protologue; we have not assumed his types are all in B. The collections of Edward Palmer made in the southwestern United States and Mexico were numbered for each collecting trip (McVaugh 1956), so care must be taken in assuming collections with the same number are duplicates, localities and years must also be taken into account.

D’Arcy (1974a) cited “type”, “syntype” or “lectotype” for many of the names treated here in his treatment of Solanum for Flora of Panama. He explicitly cited some of these as “lectotype” and we treat these as validly published lectotypifications because his intention was clear. We also treat his citations as “type” coupled with the citation of a single herbarium as unintentional (“inadvertent”) lectotypifications (e.g., Prado et al. 2015), following the stipulations of Art. 7.11 of the Code (Turland et al. 2018).

Type specimens with sheet numbers are cited with the herbarium acronym followed by the sheet number (e.g. SD [acc. # 6543]); barcodes are written as a continuous string in the way they are read by barcode readers (e.g., G00104280, MO-1781232), with the exception of those herbaria (e.g., A, GH, NY, US) where the barcode consists of only a number; here we have added the acronym to the string. For widely distributed and adventive species we have cited only types based on material from the Americas; the synonymy for S. americanum, S. nigrum, and S. villosum in particular is extensive and includes many names based on Old World collections. Details of names based on types from outside the Americas can be found in Särkinen et al. (2018) or on Solanaceae Source (www.solanaceasoursce.org).

Identities of all collections seen for this study are in Supplementary materials sections (Index to Numbered Collections; Suppl. material 1) and full searchable specimen details are available on the Solanaceae Source website (www.solanaceaesource.org), in Suppl. material 3 and in the dataset for this study deposited in the Natural History Museum Data Portal (https://doi.org/10.5519/0079673). We have not included traditional specimen citations in the main body of this paper but provide these as Suppl. material 2 (also see Tables 3 and 4). For all taxa we cite only specimens from the Caribbean, North and Central America, but Suppl. material 3 and the data set on the NHM Data Portal (https://doi.org/10.5519/0079673) include all material seen for all species treated here.

Citation of literature follows BPH-2 (Bridson 2004) with alterations implemented in IPNI (International Plant Names Index, http://www.ipni.org) and Harvard University Index of Botanical Publications (http://kiki.huh.harvard.edu/databases/publication_index.html). Following Knapp (2013) we have used the square bracket convention for publications in which a species is described by one author in a publication edited or compiled by another, the traditional “in” attributions such as Dunal in DC. for those taxa described by Dunal in Candolle’s Prodromus Systematis Naturalis Regni Vegetabilis. This work is cited here as Prodr. [A.P. de Candolle] and the names are thus attributed only to Dunal. For “ex” attributions we cite only the publishing author, as suggested in the Code (Turland et al. 2018). Standard forms of author names are according to IPNI (International Plant Names Index, http://www.ipni.org).