Members of the Morelloid clade are annual to perennial herbs or shrubs, often woody at the base. South American taxa are much more diverse in habit (Fig. 2) than in the rest of the clade’s range (e.g., Särkinen et al. 2018; Knapp et al. 2019). Here, species range from annual herbs (e.g., S. triflorum) or large coarse perennial herbs (e.g., S. pilcomayense) to short-lived somewhat woody perennials (e.g., S. arequipense) to woody shrubs (e.g., S. gonocladum). Stems are often weak, and occasionally somewhat scrambling, but can reach 5 m in height (e.g., S. cochabambense). Plants of all species usually have herbaceous upper stems, even if the base is woody. The stems can be terete (e.g., S. americanum), angled (e.g., S. antisuyo) or strongly winged throughout (e.g., S. marmoratum); this can be a useful character for identification of herbarium specimens, but note that within species variation is common.

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 phyllotactic 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; when growth of the axes is suppressed, the leaves appear paired (geminate) at a node (Danert 1958). Further fusion of axes can give rise to inflorescences arising at the node and appearing to be opposite the leaves (Danert 1970). Most members of the Morelloid clade have difoliate sympodial units with leaves usually strongly paired (geminate) at the nodes.

“Spinose” processes are common on herbaceous stems in some species of black nightshades (see Särkinen et al. 2018). They usually occur along the angles of upper parts of larger stems and are often decurrent from leaf bases (Fig. 2D). These are not true prickles, like those found in the “spiny” solanums (Leptostemonum clade, Whalen 1984; 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. In South American morelloid species spinose processes are prominent and always present in some species, such as S. salamancae, while in others (e.g., S. huayavillense) individual plants vary. Their absence, however, can be diagnostic when combined with other characters.

Species of the Morelloid clade have simple entire, shallowly toothed, deeply 3–5 lobed or deeply pinnatifid leaves that are generally elliptic or ovate in outline (see Fig. 2 and species descriptions). As with other vegetative characters in this group, leaf morphology can be extremely variable within a species or even in a single plant. Basal stem leaves are usually larger than those at the tips, and in some species (e.g., S. gonocladum) plants from extremely arid conditions have very small leaves.

Leaf margins vary from entire to deeply sinuate, lobed and pinnatifid. In species with deeply pinnatifid leaves, a wing of leaf blade is always present along the midrib, thus leaves are not strictly pinnate. Solanum annuum and S. salicifolium have pinnatifid and simple leaves on the same stems (Fig. 2H); other species, such as S. triflorum, exhibit considerable variation between plants, from deeply pinnatifid to almost entire leaves. Simple leaves with variously entire or toothed margins are common in the group. In those species with predominantly simple entire leaves at least some specimens have been examined with shallowly toothed leaf margins. In these individuals the teeth often occur only in the basal half to third of the leaf blade. The leaf blade in members of the Morelloid clade is often somewhat decurrent onto the petiole and the leaf base is then 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. Some species have almost sessile leaves (e.g., S. gonocladum, S. salicifolium, S. sinuatirecurvum, S. weddellii) where no abrupt narrowing of the leaf base onto the petiole occurs. The cultivated S. scabrum (in South America only known from Brazil) has relatively long petioles relative to leaf size (see Särkinen et al. 2018).

Trichomes in species of the Morelloid clade are simple or branched (e.g., S. pallidum, Fig. 2F), but never stellate (Seithe 1962). The simple trichomes are usually 1–6-celled and uniseriate; dendritic trichomes are similarly uniseriate and relatively few-celled. Occasionally the trichome base is enlarged with the lowermost cell much larger than more distal cells and these enlarged bases persist as spinose processes on stems (Figs 2D, 149A; sometimes called ‘pseudospines’ by other authors). Much importance has been placed on differences in density of pubescence as a taxonomic character, but pubescence within taxa is continuously variable and apparently also related to environment, with plants growing in sunny sites 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). 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 (see Subils 1989); in these plants eglandular trichomes dominate. In the species descriptions for this revision we indicate when trichomes are glandular, but if no state is indicated, this means they are eglandular.

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 show 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 heterogenous distributions of glandular and eglandular individuals in some morelloid species.

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. 3A); this is the case across the clades of Solanum (but see the Pteroidea clade with axillary inflorescences, Knapp and Helgason 1997; Tepe and Bohs 2010). Inflorescences usually arise internodally through axis fusion (Danert 1958, 1967; see above) or appear to arise opposite the geminate leaves (e.g., S. dianthum, S. sarrachoides) especially on very young shoots (e.g., S. americanum). The inflorescences of some species (e.g, S. riojense) are terminal with little or no continued shoot growth.

The basic inflorescence structure is an unbranched or variously branched scorpioid cyme. Most members of the Morelloid clade have unbranched (simple) or merely forked (once-branched) inflorescences, but some species (e.g., S. cochabambense, S. corymbosum) have inflorescences that consistently branch more than once (Fig. 4B, F). The degree of branching in some species of the group may also depend upon plant or inflorescence age (e.g., S. leptocaulon). In all Solanum species the inflorescence expands from the tip producing flowers in a proliferating manner (Lippman 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 condensed cymes, termed “sub-umbellate” inflorescences, where the flower-bearing portion is very short and the pedicels are all very closely spaced and congested at the very tip of the inflorescence (e.g., S. americanum, S. interandinum). These inflorescences are not true umbels, but are described as such in much previous literature, usually as umbellate or subumbellate cymes (e.g., Edmonds and Chweya 1997; Edmonds 2012). Both peduncles and pedicels usually have pubescence like that of the stems and leaves, or somewhat reduced distally. Solanum huayavillense is unusual in always having a pubescent inflorescence even in plants where the stems and leaves are glabrous.

Pedicels in flower are usually deflexed or spreading, and pedicel position in flower and fruit can be a good species-level character for identification but 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. gonocladum, S. macrotonum) or weakly (e.g., S. dianthum, S. fiebrigii) deflexed in some species. Other species have markedly spreading pedicels in fruit (e.g., S. americanum). Pedicels in the Morelloid clade have an abscission zone at the very base, and if and when pedicels abscise, the scars are generally flush with the inflorescence axis or sometimes on a tiny, raised stump. Pedicel persistence after fruit ripening and abscission can be important species character in this group (S. americanum, S. antisuyo), but in South America most species do not have persistent pedicels. In S. americanum the ripe berries fall without the pedicels, thus the pedicel is left behind and persists. The presence of old pedicels can be useful for identification of non-flowering herbarium specimens.

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, S. dianthum), and the lobes are extremely variable in size and shape from small-deltate and rounded (e.g., S. antisuyo) to long-triangular (e.g., S. glandulosipilosum, S. physalidicalyx, S. sinuatiexcisum). 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. fragile, S. grandidentatum, S. marmoratum) or appressed to the berry (e.g., S. corymbosum, S. nigrescens). The calyces of several species are accrescent in fruit with the calyx lobes expanding to envelop the entire to almost the entire berry (e.g., S. physalidicalyx, S. tweedieanum). In these species the calyx base in fruit is often invaginate (e.g. S. gilioides, Fig. 62H).

In common with most species of Solanum, members of the Morelloid clade have 5-merous sympetalous corollas that are variously lobed (see Fig. 3 for representative corollas in South American species). Floral mutants are often observed, where 4–6-merous corollas can occur on individual plants that are otherwise 5-merous (e.g., S. americanum). Colour is generally white or pale violet-tinged (see Fig. 3 and individual species illustrations), but anthocyanin pigmentation can vary depending on environmental growth conditions and in most white-flowered species at least some individuals with purple and violet flowers have been recorded. A single species of the group has pale yellow flowers (S. huayavillense). At the base of the corolla tube there can be 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 but can be dark purple or ringed with blackish purple pigment (Fig. 3D, F, H). This eye is usually similar in texture to the rest of the corolla and not shiny as occurs in the Dulcamaroid clade (Knapp 2013). The colours of the eye usually disappear in herbarium specimens and are rarely noted on labels.

Corollas in the Morelloid clade vary from stellate, deeply stellate, rotate-stellate or pentagonal to occasionally campanulate, and corolla lobes from small-deltate to long-triangular (Fig. 3). Most species have stellate corollas where the lobes and tube are approximately of equal length, and the lobes can be spreading (held horizontally), reflexed or somewhat cupped. Solanum triflorum has deeply stellate corollas, with narrow, reflexed corolla lobes, while S. corymbosum has corollas with the lobes approximately the same length as the tubular portion, and the lobes are not strongly reflexed at anthesis. Pentagonal, spreading rotate-stellate corollas with small lobes occur in some species (e.g., S. annuum, S. caesium, S. weddellii); in S. caesium, the entire corolla is reflexed at some points during anthesis. A few species have campanulate corollas (Fig. 3A) where the lobes are tiny and never reflexed but rather somewhat cupped (e.g., S. albescens, S. fiebrigii, S. leptocaulon, S. sinuatiexcisum); in these species descriptions we have recorded corolla length rather than diameter. These characters, particularly those of the degree to which corolla lobes are reflexed, can be very difficult to see in herbarium specimens. The corolla lobes can be more or less reflexed through the life of the flower as is seen in many other groups of solanums (e.g., Dulcamaroid clade, ANS clade, see Knapp 2013; Knapp and Vorontsova 2016) where flowers last more than one day. Lobes often are spreading on day one, become reflexed to strongly reflexed on subsequent days, and as the flower ages, lobes become spreading again. In some species (e.g., S. cochabambense, S. leptocaulon) flower size can appear extremely variable within plants (Fig. 3H); this may be due to corolla expansion through the life of the flower as has been demonstrated in Lycianthes (Dean 2001; Dean et al. 2020).

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; amongst the species treated here S. marmoratum has the smallest corollas and S. albescens 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. Some species have corolla surfaces that are densely puberulent/pubescent where the surfaces are exposed in bud, in these taxa the interpetalar tissue (that is folded within the bud before anthesis) is usually glabrous.

The stamens of members of the Morelloid clade are mostly equal to very slightly unequal in size and length. In those taxa with slightly unequal stamens the basal-most filament appears to be somewhat longer, but this has not been assessed quantitatively as is the case in other Solanum species (Bohs et al. 2007; Aubriot and Knapp 2022). The differences in length are so small that they are unlikely to influence pollinator behaviour as is the case for strongly enantiostylous solanums (e g., S. rostratum Dunal of the Androceras clade; see Bowers 1975; Vallejo-Marín 2022). The filament tube and filaments are variously pubescent adaxially. The trichomes on filaments are eglandular, 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 distinct. Filament length in comparison to anther length can be a useful character for distinguishing species. In most species of morelloids treated here the free portion of the filament is about half the anther length, some (e.g., S. americanum) have the anthers and filaments of equal length, while other species are characterised by long filaments in relation to anther length (e.g., S. subtusviolaceum). The length of filaments can affect the biophysical properties of anther vibration and thus perhaps vibratile pollination (e.g., Timerman et al. 2014; Switzer and Combes 2016), and may be an important characteristic involved in speciation in this group. In some species (e.g., S. marmoratum) filaments elongate throughout anthesis, beginning shorter than the anthers and much longer at the end of flowering.

Anthers of members of the Morelloid clade conform to the poricidal morphology of all other species of Solanum (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 tapering and somewhat beaked anthers of S. woodii (Fig. 185C) are unique in the group; when originally described (Särkinen and Knapp 2016) this species was thought to be closely related to S. anomalostemon S.Knapp & M.Nee, an unusual species with heart-shaped anthers and no close relatives (Gagnon et al. 2022). The anthers are loosely connivent, and not connected by either “glue” (as in S. dulcamara L., 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, where anthers vary from less than 1 mm (S. americanum, S. marmoratum) to ca. 5 mm long (S. dianthum, S. gonocladum, S. hunzikeri, S. tweedieanum); in such small flowers, small differences can be very important.

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 (Fig. 3B, E) or slightly curved (Fig. 3C) 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, S. marmoratum, S. weddellii) 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 studied so far have been self-compatible (Edmonds 1979a; Schilling and Heiser 1979; Eijlander and Stiekema 1994; Olet 2004). We have observed marked difference in style length and exsertion over the course of anthesis in S. marmoratum (see species description) and so have described this character as included, exserted or long-exserted without giving specific measurements, as the detailed floral biology of morelloid species is so poorly known. Flowers collected at different stages of anthesis can be quite disparate and little is known about changes in style length over the course of anthesis for the majority of species.

Species of the Morelloid clade do not have markedly heterostylous flowers. The stigma is either very minutely capitate (e.g., S. nigrescens) or larger and more obviously globose-capitate (e.g., S. corymbosum, S. radicans) and sometimes bilobed (e.g., S. arequipense, S. weddellii). In Solanaceae the ovules are anatropous and the seeds non-arillate.

As with all species of Solanum, the fruit is a bicarpellate berry. Fruits of members of the Morelloid clade are small (usually less than 1 cm in diameter) and juicy, with thin pericarp that is often shiny (Fig. 4). Most species have globose berries, but those of S. palitans are somewhat flattened and those of S. tripartitum are conspicuously bilobed (Fig. 4A). Berry colour is usually green, yellowish green or varying shades of purple and purple-black (Fig. 4D–G); immature berries are usually described as green on herbarium labels. The berries of S. tweedieanum are almost cream-coloured when ripe and could be described as whitish green. Marbling with white occurs in several species with green mature berries (e.g., S. marmoratum, S. physalifolium, Fig. 4C); these markings often disappear in herbarium specimens and are not usually recorded on labels. Solanum palitans has yellow translucent berries and S. corymbosum and S. tripartitum orange to red berries that are more opaque (Figs 4B, 42D, 108D, 176D). Colour polymorphisms are common in species of this group; Solanum aloysiifolium, for example, has 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 those of older specimens. Some species of South American morelloids have berries that turn from green to mottled purple or purple-tinged as they ripen (e.g., S. interandinum) so berry colour is often difficult to interpret from herbarium labels.

The pericarp (epicarp) of the berries is thin and either matte (e.g., S. aloysiifolium, S. chenopodioides) or shiny (e.g., S. americanum, S. gonocladum, S. physalifolium). 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 (S. americanum, S. scabrum). This character is rarely mentioned on herbarium labels.

Berries of members of the Morelloid clade contain small, hard inclusions commonly referred to as stone cells or brachysclereids (Bitter 1911, 1914a), known also from other groups of non-spiny solanum such as the Pachyphylla clade (ex-Cyphomandra Sendtn., Bohs 1998) and the Archaesolanum clade (Symon 1994). These concretions are composed of modified sclerenchyma cells with massively enlarged cell walls (Fig. 4H); 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 (1914a) suggested that they existed in an evolutionary series in the family, with more “advanced” taxa lacking stone cells 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). Stone cells in the Morelloid clade are usually quite small and are always more or less spherical, ca. 0.5 mm in diameter, and brown to white in colour; they sometimes have irregular surface patterning. Stone cells can usually be easily seen in dried specimens without dissecting the berry (see fig. 1 in Bitter 1914a; Fig. 4I); 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, except for in the members of the Radicans clade where there are consistently two large apical inclusions and varying numbers of smaller stone cells scattered in the berry flesh. The number of stone cells is usually relatively consistent within a species, and varies from absent (e.g., S. annuum, S. chenopodioides, S. fragile, S. scabrum) to (1)2–4(-6) (e.g., S. arequipense, S. macrotonum, S. nigrescens) to more than 10 (e.g., S. echegarayi, S. furcatum, S. triflorum). Solanum americanum varies from having 0 to 4 stone cells per berry. Bitter (1914a) reported that in crosses involving Morelloid species with and without stone cells hybrid progeny had stone cells present in the fruit, indicating that this was an inherited character. Cultivated species (e.g., S. scabrum) tend to lack stone cells; this may be related to human-mediated selection.

Members of the Morelloid clade usually have flattened seeds, like many other solanums. Seed shape varies from rounded to reniform and markedly kidney-shaped. Most species have teardrop shaped seeds, with the hilum and micropyle at one of the short ends of the seed (Fig. 4H), which is unusual as most species of Solanum have reniform seeds. Seed size varies from 1–3 mm long, 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). Seed number per berry in the Morelloid clade is generally quite high, with usually 30–50 seeds in each berry, but S. annuum consistently has only one or two seeds per 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). Most 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; 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) seeds appear pubescent; seed measurements here include these projections. Edmonds (1983) examined seed coat patterns in some members of the Morelloid clade (as Solanum section Solanum) and found no useful variation for delimiting either species or species groups. Solanum. annuum, S. gilioides and S. weddellii (previously recognised as section Chamaesarachidium; Barboza 2003) have tuberculate seeds (Fig. 18M), a character state found nowhere else in the Morelloid clade (interestingly, tuberculate seeds are also found in desert-dwelling species of the unrelated spiny Androceras clade; Whalen 1979).

Chromosome numbers in the Morelloid clade are variations on the base number of 12 (Table 1); most species are diploid, but several tetraploid species of uncertain parentage are found in the clade. The chromosomes are very small; median, submedian and subterminal centromeres have been reported (Bhiravamurty 1975). 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 Chiarini et al. 2018; Särkinen et al. 2018). Polyploidy is common in the members of the group found outside the Americas, but apparently less so in South American species. Variation in ploidy level within a species is not common in Solanum, but some species appear to have populations with different chromosome numbers (e.g., S. interandinum, S. macrotonum, see species descriptions); similar variation occurs elsewhere in Solanum in the potatoes (see Spooner et al. 2014). Genome sizes in unreplicated gametic nuclei (C-values) of morelloid species vary between 0.60 pg in S. tripartitum and 3.10 pg in S. nigrum (Bennett and Leitch 2019).

Many chromosome counts are 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 our own counts or those that are vouchered and for which we have verified the specimen in question. Many of the numbers reported in previous publications (e.g., Edmonds 1972, 1977, 1978b, 1986; Edmonds and Chweya 1997) are based on plants grown from wild collected seed, but we have not been able to trace the vouchers and so these are not reported here. Where the count based on a voucher that we have not located for verification is the only one for a species we indicate by citing the count as “reported as”. We report chromosome numbers as they are presented in the publications – either as meiotic counts (n) or mitotic counts (2n).

Members of the Morelloid clade are usually plants of disturbed habitats and occur in landslides, along roads and streams, and at the edges of cultivated fields (Fig. 5). Many of the species have broad elevational ranges (e.g., S. americanum) and extremely broad geographical distributions (see Tables 2, 3). Species diversity in South America is highest in the central and southern central Andes (see Fig. 1C); Bolivia is home to 41 species and Argentina 38 species.

The largest number of endemic species is found in Argentina (six endemic of 38 species, see Table 2) followed by Bolivia (three endemic of 41 species) and Brazil (two endemic of eight species) and Peru (a single endemic of 25 species). Endemic species in Argentina occupy a wide range of habitats, from the low elevation pampas in the centre of country (S. marmoratum) to the high Andes (S. riojense), but most are from the Andean foothills, often in the drier habitats defined as prepuna (Cabrera 1976). The high diversity in Bolivia is due to sharing of species from both the south and north; Bolivia shares 16 species with Argentina but not with Peru, and 14 species with Peru and Ecuador but not with Argentina. Eight species of morelloids are found across all three countries (Argentina, Bolivia and Peru). We list the status and general distribution of the species in the group in Table 2, and in Table 3 document country distribution from herbarium specimens (see Materials and methods).

The NOA (“nor-oeste-Argentina”, sensu Aagensen et al. 2012), where Argentina borders Bolivia, is home to many of the endemic and semi-endemic species treated here. This area of endemism is composed of several overlapping more discrete areas of endemism in northern Argentina, such as the so-called Jujuy, Tucumán and Jujuy-Tucumán areas of endemism (sensu Aagensen et al. 2012). Several species previously considered as Argentine endemics (e.g., S. huayavillense, S. hunzikeri, S. zuloagae) have only recently been collected in southwestern Bolivia, confirming the suggestion of Aagensen et al. (2012) that the northern boundary of their NOA (border of Argentina and Bolivia) could change with future collecting. The 16 shared species between Bolivia and Argentina all occur within this previously defined area of endemism.

In contrast to our findings from North America, Europe and Australia (see Särkinen et al. 2018; Knapp et al. 2019), adventive species are rare to non-existent in South America. The single clearly introduced species in South America is S. scabrum, only known to us from two old collections (see species description). It is likely that this plant, widely cultivated in Africa for both its leaves and fruits, was brought to Brazil by enslaved Africans during the 19^th century. Unlike S. aethiopicum L. (“Gilo” an African species of the Leptostemonum Clade, see Vorontsova and Knapp 2016), whose use is widespread in Brazil today, S. scabrum appears not to have persisted in cultivation.

South America appears to have been a source, rather than a sink, of adventive species; several South American members of the group (e.g., S. nigrescens, S. nitidibaccatum) are registered as noxious weeds of agriculture (see below) in both Europe and North America (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).

Like most 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 (Fig. 3G) and rotate around the flower (Buchmann et al. 1977). Bees then groom the pollen from their bodies and pack it into their corbiculae (hollow areas on the hind legs), but they cannot reach the area of the venter that contacts the stigma of the next flower and so pollen is transferred from flower to flower. Smaller bees visit and buzz individual anthers (Symon 1979), but do not usually contact the stigma and thus in solanums with large flowers these small bees 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 the morelloid S. douglasii Dunal in the southwestern United Sates 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 in this group.

The juicy berries with thin pericarp (skins) of members of the Morelloid clade that are typical of bird-dispersed fruits (Knapp 2002b). Studies of dispersal of morelloid species have mostly been done on those 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 mammal 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.

Glycoalkaloid concentrations are very low in ripe berries of S. americanum and other members of the Morelloid clade that have been tested (Cipollini et al. 2002), and levels are similar across the clade. 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 constipating 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).

Preliminary conservation assessments for all species of the Morelloid clade treated here (including introduced taxa) are presented in Table 4. Many of these species can be assigned the status of Least Concern; we have based our assessments primarily on Extent of Occurrence (EOO), because Area of Occurrence (AOO) is highly influenced by collection effort or georeferencing deficit but see individual species treatments for discussion.

Most morelloid species are weedy and widely distributed; outside of the Americas, many species are also cultivated (e.g., S. scabrum, S. tarderemotum Bitter, 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). Several of the South American species that are adventive in other parts of the world were transported via wool, particularly from Argentina (e.g., S. chenopodioides). 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. Most of the South American species of morelloids, however, are confined to the continent; some are widespread (e.g., S. cochabambense, S. nigrescens) while others have quite narrow distributions (e.g., S. annuum, S. caatingae). It is possible that many of the species known from few collections are under-collected due to the common perception that all these species are the same, common, weedy and thus not worth collecting.

The Morelloid clade

The Morelloid clade, sensu Bohs (2005) and Särkinen et al. (2013, 2015b)

Solanum grad. ambig. Maurella Dunal, Hist. Solanum 119, 151. 1813. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum section Morella Dumort., Fl. Belg. 39. 1827. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum section Inermis G.Don, Gen. Syst. 4: 400. 1838. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum grad ambig. Morella G.Don, Gen. Syst. 4: 411. 1838. Lectotype. S. nigrum L. (designated by D’Arcy 1972).

Solanum section Pachystemonum Dunal, Prodr. [A. P. de Candolle] 13(1): 28, 31. 1852. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum subsection Morella Dunal, Prodr. [A. P. de Candolle] 13(1): 28, 44. 1852. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum section Campanulisolanum Bitter, Repert. Spec. Nov. Regni Veg. 11: 234. 1912. Lectotype species. S. fiebrigii Bitter (designated by Seithe 1962).

Solanum section Episarcophyllum Bitter, Repert. Spec. Nov. Regni Veg. 11: 241. 1912. Lectotype species. S. sinuatirecurvum Bitter (designated by Seithe 1962).

Solanocharis Bitter, Repert. Spec. Nov. Regni Veg. 15: 153. 1918. Type species. Solanocharis albescens (Britton) Bitter (= Solanum albescens (Britton) Hunz.)

Solanum section Morella (Dunal) Bitter, Bot. Jahrb. 54: 416, 493. 1917. Lectotype species. S. nigrum L. (designated by D’Arcy 1972).

Solanum section Chamaesarachidium Bitter, Repert. Spec. Nov. Regni Veg. 15: 93. 1919. Type species. S. chamaesarachidium Bitter (= S. weddellii Phil.).

Solanum series Transcaucasica Pojark., Bot. Mater.Gerb.Inst. Komorova Akad. Nauk S.S.S.R. 17: 332. 1955. Lectotype species. S. transcauscasica Pojark. (= S. villosum Mill.) (designated by D’Arcy 1972 [as type]).

Solanum series Alata Pojark., Bot. Mater.Gerb.Inst. Komorova Akad. Nauk S.S.S.R. 17: 336.1955. Type species. S. alatum Moench [nom. et typ. cons.] (= S. villosum Mill.) (designated by D’Arcy 1972 [as type]).

Solanum series Pseudoflava Pojark., Bot. Mater.Gerb.Inst. Komorova Akad. Nauk S.S.S.R. 17: 338. 1955. Type species. S. pseudoflavum Pojark. (= S. villosum Mill.) (designated by D’Arcy 1972 [as type]).

Solanum section Parasolanum Child, Feddes Repert. 95: 142. 1984. Type species. S. triflorum Nutt.

Solanum section Solanocharis (Bitter) Child, Feddes Repert. 95: 147. 1984, as ‘Solancharis’ Type species. Solanum albescens (Britton) Hunz.

Solanum section Dulcamara (Moench) Dumort. subsect. 2 “herbaceous plants confined to the central Andes” of Nee (1999: 295) [includes the species of Child’s section Parasolanum excluding the type]

Solanum section Solanum subsects. 1 “Solanum”, 2 “Glandular pubescent group”, 3 “Campanulisolanum”, 4 “Chamaesarachidium” and 6 “Episarcophyllum” of Nee (1999: 306–308), excluding his subsect. 5 “Gonatotrichum” [now recognised as being part of the Brevantherum clade, see Stern et al. 2013].

Solanum series Lutea Pojark. ex Ivanina, Bot. Zhurn. (Moscow & Leningrad) 85(6): 144. 2000. Type species. S. villosum Mill.

Description. Annual to perennial herbs, subshrubs or shrubs, often woody at the base; unarmed. Stems terete or angled, sometimes hollow, lacking true prickles but sometimes with spinose processes along the angles, glabrous or pubescent with simple or branched (forked and dendritic) uniseriate trichomes, these eglandular or glandular. Sympodial units difoliate, trifoliate or plurifoliate, the leaves usually not geminate. Leaves simple with entire or variously dentate or lobed margins or occasionally deeply pinnatifid, concolorous or less commonly discolorous, glabrous to densely pubescent with eglandular and/or glandular simple or branched (only in South America) uniseriate trichomes; petioles generally well developed, the leaves sessile in some species. Inflorescences opposite the leaves or internodal, unbranched, forked or many times branched, not bracteate (except in S. triflorum where a single bracteole sometimes present), with few to many (up to 100) flowers, these clustered at the tip (umbelliform or sub-umbelliform) or spaced along the axis; peduncle various, usually not longer than the inflorescence branches; pedicels articulated at the base (in S. interius Rydb. of North America the basal flower with the articulation slightly above the base), either flush with the axis or leaving a small stump, occasionally with a cup-shaped base in fruit (S. caesium). Flowers 5-merous (occasionally 4-merous or fasciate and 6–7-merous in S. scabrum), actinomorphic to very slightly zygomorphic in filament length or calyx lobe length, cosexual (hermaphroditic). Calyx with the lobes deltate to spathulate to long-triangular. Corolla deeply to broadly stellate or pentagonal and rotate-stellate, rarely campanulate, white or purplish-tinged to lavender or purple, rarely pale yellow (S. huayavillense), usually with an “eye” at the base of the lobes of a contrasting colour (yellow, green or dark purplish black), the lobes spreading or reflexed at anthesis. Stamens equal or very slightly unequal, the filaments equal to very slightly unequal, glabrous or more usually densely pubescent with tangled uniseriate weak-walled simple uniseriate trichomes, the anthers ellipsoid (slightly tapering in S. scabrum; somewhat beaked in S. woodii) and connivent, with distal pores that elongate to slits with drying and/or age. Ovary conical, glabrous or occasionally very minutely puberulent; style straight or curved and bent, usually pubescent with simple uniseriate trichomes in the lower half, exserted from the anther cone, sometimes only very slightly so; stigma minutely capitate to capitate or clavate. Fruit a globose, flattened (depressed) or ellipsoid juicy berry with thin pericarp, green, blackish purple, yellow or reddish orange at maturity, occasionally marbled with white (e.g., S. physalifolium), opaque or translucent, glabrous; fruiting pedicels spreading or deflexed, occasionally secund, either remaining on the plant after fruit drop (persistent) or not; fruiting calyx lobes spreading, reflexed, appressed or accrescent at fruit maturity; accrescent lobes appressed or inflated, the base sometimes invaginate. Seeds mostly flattened and teardrop shaped, occasionally reniform or rounded, yellow or tan to dark brown, the surfaces minutely pitted or in a few species tuberculate (e.g., S. annuum, S. gilioides, S. weddellii). Stone cells absent or present, if present few to numerous. Chromosome number: n = 12, 24, 36 (see Särkinen et al. 2018, and individual species treatments).

Distribution. A worldwide species group occurring in on all continents except Antarctica, but with highest species diversity in the central and southern Andes and Africa.

Discussion. In the synonymy of the group presented here we have included all groups that are members of the clade as we define it; for more detailed discussion of morphology and group definition see Särkinen et al. (2015b). Solanum nigrum is the lectotype species of Solanum (Hitchcock and Green 1929), and thus if the Morelloid clade were to be formally recognised at the infrageneric level it would necessarily be called Solanum independent of rank (as recognised by Seithe 1962).

Members of the Morelloid clade are among the most widely collected of solanums, in part because are they are herbaceous, widespread and often weedy. They are also among the most difficult to identify, due to their extreme vegetative plasticity (see Morphology above) and their lack of striking distinguishing characters. Combinations of characters are most useful for identification, and we have included these in the species treatments as well as in the keys. Geography is very helpful in assisting with species identification in this group, but the large number of potentially invasive and introduced species means one must exercise caution if a species is not readily identifiable and consider species not currently known from the area (taking into account variation of course).

The Morelloid clade suffers from two extreme sorts of taxonomic recognition issues. Firstly, in many parts of the world all taxa have been treated as a single highly variable species (usually S. nigrum, see for example Sendtner 1846) and local endemic taxa are overlooked. Secondly, and especially in Europe in the late 19^th and early 20^th century, many minor variants were described and were then transferred and recombined at different taxonomic levels, creating a confusing morass of names, many of which lack types. The latter is unfortunate because of the nomenclatural work entailed in sorting out the identities and types for these names is time-consuming and often quite difficult (see Särkinen et al. 2018), but the former is more serious, because endemic taxa have been overlooked (e.g., S. caatingae, S. marmoratum) and thus have possibly been placed at risk due to their being equated with widespread invasive weeds.

These plants are all remarkably superficially similar and distinguishing features often involve minute differences in anther length; geography is often a good indicator of what species one has, but not always. Combinations of characters are useful in identifying these species and to this end we provide a synoptic character list after the main dichotomous key.

A global multi-access key that includes all of the taxa in this monograph can be found at http://xper3.fr/xper3GeneratedFiles/publish/identification/-3915026624309343770/mkey.html and under the identification tab on Solanaceae Source. Country-level keys have been published for Argentina (Knapp et al. 2020) and Brazil (Knapp and Särkinen 2018). Geography is only indicated in couplets that terminate in a species name.

Many of these species are polymorphic in a number of these characters; please refer to species descriptions for details.

Rhizomatous herbs or subshrubs: S. echegarayi, S. profusum, S. pygmaeum, S. rhizomatum, S. riojense, S. sinuatirecurvum, S. tweedieanum.

Plants with adventitious roots: S. alliariifolium, S. corymbosum, S. palitans, S. radicans, S. tripartitum.

Apparently annual plants: S. americanum, S. annuum, S. corymbosum, S. gilioides, S. grandidentatum, S. michaelis, S. nitidibaccatum, S. palitans, S. physalifolium, S. pseudoamericanum, S. sarrachoides, S. triflorum, S. weddellii, S. woodii.

Large shrubby plants: S. americanum, S. arequipense, S. arenicola, S. chenopodioides, S. cochabambense, S. enantiophyllanthum, S. fiebrigii, S. furcatum, S. interandinum, S. juninense, S. macrotonum, S. nigrescens, S. pallidum, S. paucidens, S. pilcomayense, S. polytrichostylum, S. pseudoamericanum, S. salicifolium, S. sinuatiexcisum, S. subtusviolaceum, S. zuloagae.

Plants from robust woody stems: S. echegarayi, S. fragile, S. gonocladum

Stems strongly winged (wings or angles > 0.4 mm wide): S. corymbosum, S. fragile, S. grandidentatum, S. interandinum, S. marmoratum, S. pentlandii, S. radicans, S. salamancae, S. tiinae.

Stems with “spinose” processes: S. americanum, S. arequipense, S. cochabambense, S. dianthum, S. interandinum, S. macrotonum, S. marmoratum, S. nigrescens, S. paucidens, S. pentlandii, S. physalifolium, S. radicans, S. rhizomatum, S. salamancae, S. scabrum, S. tiinae.

Stems with long glandular trichomes: S. arenicola, S. caatingae, S. caesium, S. fiebrigii, S. fragile, S. gilioides, S. glandulosipilosum, S. grandidentatum, S. hunzikeri, S. juninense, S. michaelis, S. nitidibaccatum, S. physalidicalyx, S. physalifolium, S. profusum, S. sarrachoides, S. sinuatiexcisum, S. subtusviolaceum, S. tweedieanum, S. woodii.

Stem pubescence strongly antrorse: S. gonocladum, S. leptocaulon, S. salamancae, S. salicifolium, S. tiinae, S. triflorum.

Stem pubescence soft and curling or tangled: S. albescens, S. dianthum, S. riojense, S. sinuatirecurvum, S. weddellii.

Stem pubescence dendritic (branched): S. pallidum.

Leaves sessile (petiole absent): S. echegarayi, S. gilioides, S. huayavillense, S. hunzikeri, S. leptocaulon, S. profusum, S. riojense, S. salicifolium, S. sinuatirecurvum, S. tiinae, S. tripartitum.

Leaves pinnatifid (compound or lobed more than halfway to the midrib): S. annuum, S. gilioides, S. palitans, S. radicans, S. salicifolium, S. tripartitum, S. triflorum.

Leaves deeply and regularly 3-lobed: S. palitans, S. tripartitum.

Leaves deeply and regularly 3-lobed: S. radicans.

Leaves fleshy, the margins often revolute: S. echegarayi, S. riojense, S. sinuatirecurvum, S. triflorum, S. weddellii.

Leaves glabrous: S. corymbosum, S. echegarayi, S. huayavillense, S. palitans, S. tripartitum.

Leaves with ciliate margins: S. huayavillense, S. zuloagae.

Bud globose: S. americanum, S. annuum, S. corymbosum, S. fragile, S. grandidentatum, S. palitans, S. pentlandii, S. radicans, S. tripartitum, S. weddellii.

Buds narrowly elliptic: S. aloysiifolium, S. glandulosipilosum, S. polytrichostylum, S. triflorum.

Inflorescences opposite the leaves: S. dianthum, S. physalidicalyx, S. sarrachoides.

Inflorescences many times branched (more than forked): (S. aloysiifolium), S. cochabambense, S. corymbosum, S. fiebrigii, S. huayavillense, S. interandinum, S. juninense, S. pallidum, S. pentlandii, (S. polytrichostylum), S. tripartitum, S. zuloagae.

Corolla deeply stellate, interpetalar tissue appearing absent: S. aloysiifolium, S. arenicola, S. chenopodioides, S. salicifolium, S. triflorum.

Corolla pentagonal or broadly rotate: S. annuum, S. caesium, S. corymbosum, S. gilioides, S. palitans, S. physalifolium, S. riojense, S. sarrachoides, S. sinuatirecurvum, S. weddellii.

Corolla campanulate (very shallowly lobed and cup-shaped): S. albescens, S. fiebrigii, S. leptocaulon, S. sinuatiexcisum.

Flowers (pale) yellow: S. huayavillense.

Anthers less than 1.5 mm long: S. americanum, S. annuum, S. corymbosum, S. gilioides, S. marmoratum, S. nitidibaccatum, S. weddellii.

Anthers more than 5 mm long: S. dianthum, S. gonocladum, S. hunzikeri, S. tweedieanum.

Styles long-exserted (exserted portion longer than the anthers) from the anther cone: S. arequipense, S. fragile, S. furcatum, S. pentlandii, S. pseudoamericanum.

Style included within the anther cone (or just barely exserted): S. americanum, S. marmoratum, S. weddellii.

Berries less than 1 cm in diameter: S. aloysiifolium, S. annuum, S. echegarayi, S. longifilamentum, S. paucidens.

Berries depressed or flattened (sub-ovoid): S. cochabambense, S. michaelis, S. palitans, S. radicans, S. tripartitum.

Berries ellipsoid: S. antisuyo, S. gilioides, S. weddellii.

Berries 2-lobed (easier to see in immature fruit): S. palitans, S. radicans, S. tripartitum.

Mature berries orange or yellow: S. alliariifolium, S. caesium, S. palitans, S. riojense, S. radicans.

Mature berries red: S. corymbosum, S. tripartitum.

Mature berries translucent green marbled with white: nitidibaccatum, physalifolium, marmoratum.

Mature berries shiny: S. americanum, S. nitidibaccatum, S. marmoratum, S. physalifolium, S. sarrachoides, S. scabrum.

Fruiting pedicels persistent after fruit ripening (i.e., lack of abscission): S. americanum, S. antisuyo, S. sinuatirecurvum.

Fruiting calyx accrescent (inflated or appressed): S. annuum, S. gilioides, S. hunzikeri, S. marmoratum, S. michaelis, S. nitidibaccatum, S. physalidicalyx, S. physalifolium, S. profusum, S. salamancae, S. sarrachoides, S. tweedieanum, S. weddellii.

Fruiting calyx inflated and completely enclosing the berry, invaginate at the base: S. physalidicalyx, S. salamancae.

Seeds fewer than 10 per berry: S. annuum, S. echegarayi, S. gilioides, S. huayavillense, S. sinuatirecurvum, S. weddellii.

Seeds more than 50 per berry: S. aloysiifolium, S. caatingae, S. caesium, S. fiebrigii, S. interandinum, S. juninense, S. marmoratum, S. nigrescens, S. paucidens, S. pilcomayense, S. polytrichostylum, S. pygmaeum, S. sarrachoides, S. scabrum, S. sinuatiexcisum, S. triflorum.

Seeds tuberculate: S. annuum, S. gilioides, S. weddellii.

Stone cells absent: S. americanum, S. annuum, S. antisuyo, S. arequipense, S. caatingae, S. chenopodioides, S. fragile, S. gilioides, S. grandidentatum, S. huayavillense, S. michaelis, S. nitidibaccatum, S. pentlandii, S. physalidicalyx, S. physalifolium, S. profusum, S. pseudoamericanum, S. riojense, S. scabrum, S. sinuatirecurvum, S. weddellii. S. woodii.

Stone cells 10 or more per berry: S. aloysiifolium, S. cochabambense, S. echegarayi, S. furcatum, S. glandulosipilosum, S. hunzikeri, S. interandinum, S. nigrescens, S. salicifolium, S. triflorum.