Solanum dulcamara L.

Solanum dulcamara is one of the most variable species in the Dulcamaroid group, all of which show extremes of phenotypic plasticity. It is also the most widespread, and is found throughout the northern hemisphere, in Europe and Asia from Spain to Siberia and into extreme northern Japan, and across the northern United States (reported from Florida on the PLANTS database [http://plants.usda.gov/java/profile?symbol=SODU], from where I have seen no specimens), where it is presumed to have been introduced from Europe. I can find no documentary evidence for the introduction of S. dulcamara into the New World, but early collections from North America held in BM (e.g., Bartram, Clayton) do not contain specimens of this species. The earliest collections I have seen are from the Boston area in the early 19th century (e.g., Dutton s.n.); it is possible that S. dulcamara was introduced to North America for its medicinal properties.

Some of the variation in S. dulcamara appears to be related to habitat (e.g., coastal forms with succulent leaves that have been recognised as var. marinum and S. littorale) but much of the variation is in leaf size and division, pubescence and flower color; I have been able to find no pattern related to either geography or habitat in this variation. Turesson (1922) suggested that differences in morphology related to habitat were genetic, despite his finding that in non-coastal environments thick-leaved coastal forms developed thinner, less pubescent leaves. Sun and shade leaves of S. dulcamara have been studied for physiological and some morphological properties (Clough et al. 1979a, b). Differences in morphology can occur along a single stem depending upon the shade environment. Unlike some other species in the Dulcamaroid clade (e.g., S. umbelliferum) variation does easily sort into distinguishable units, but the sheer range and complexity of the variation has led to the description of many taxa within what I recognise as a single highly polymorphic species, especially in floristic treatments from Central Asia (Pojarkova 1955; Schönbeck-Temesy 1972), where much of the variation exists.

Chemical variation in S. dulcamara has also been intensively studied in eastern Europe (Máthé and Máthé 1972, 1979); populations with pubescent individuals from the northen part of the eastern European range tended to have higher percentages of the alkaloid aglycone tomatidinol while more glabrous populations had higher concentrations of soladulcinine. The concentrations of various alkaloids were affected by the environmental conditions under which plants were grown (Máthé et al. 1975) as well as by what were presumed to be genetic (ecotypic) factors (Bernáth and Tétényi 1977). Clough et al. (1979a) and Pegtel (1985) both suggested that ecotypic differentiation did not explain the variation observed, but instead that the variability was the result of short-term phenotypic acclimatization to differing environments. A study using AFLP (Associated Fragment Length Polyomorphisms) data from Europe-wide accessions of S. dulcamara found almost no genetic variation or population structuring either geographically or in association with habitat (Golas et al. 2010).

A few of the more extreme forms have recognised at the species level, but the variation in the diagnostic features of these forms is continuous across the range of the species. Identifications of individual specimens by botanists describing these variants were occasionally inconsistent from duplicate to duplicate.
1. Plants occurring in the swampy areas around the hot springs at Lenkoran in what is now Azerbaijan were described as S. kieseritzkii; all of the collections from this locality are composed of small erect shoots connected with creeping stems and have very small inflorescences of only a few flowers.
2. Glabrous plants with simple leaves have been recognised as S. pseudopersicum; glabrous plants with divided leaves as S. kitagawae.
3. Pubescent plants with simple leaves were described as S. persicum; these tended to be from the southern part of the species range in Eurasia, but occur throughout the species’ range.
4. Large-fruited plants from the eastern margins of the Asian range have been called var. macrocarpum; these fruits also tend to be more ellipsoid than globose, but as with other characters, this occurs sporadically throughout the range of the species.
5. White-flowered plants have been given varietal or subspecific status both in Europe and the United States; polymorphism in flower color is common in Solanum in general.

Solanum dulcamara has a long history of use in medicine in Europe and in the United States. Gerard (1597:350) says “The leaves and fruit of the Bitter-sweet are in temperature hot and dry, clensing and wasting away” and cites as its “Vertues” effects on liver and spleen, against jaundice and bruising, and of its use to help breathing difficulties and as a restorative after childbirth. The common name bittersweet (or douce-amère) comes from the Latin ‘Amaradulcis’, and refers to the fact that when chewed, the twigs taste at first bitter, then sweet (Grieve 1931). Bittersweet had many uses ranging from inflammatory diseases of all kinds (such as asthma and rheumatism) to nymphomania and syphilis (Dunal 1813; Felter and Lloyd 1898); Grieve (1931: 590) states “there are few complaints for which it has not at some time been recommended.” As ‘Dulcamara’ or ‘Dulc’ (van Zandvoort 1996), the stems are used still in homeopathic medicine (Bharatan et al. 2002). It is today listed as a poisonous plant in many countries and US states (see for example the FDA at http://www.accessdata.fda.gov). Michel-Félix Dunal treated the uses and superstitions associated with this species (Dunal 1813) and concluded that the many properties attributed to bittersweet were mostly not substantiated in fact. The steroidal alkaloids responsible for the active properties of S. dulcamara were not discovered until the late 19th century, they are principally dulcamarine and solanine, the first of which is responsible for the bittersweet taste and the second for the narcotic effects (Grieve 1931).

Solanum dulcamara has been thought to be an intermediate host and possible source of primary infections for several agronomically important potato diseases such as late blight (caused by the oomycete Phytophthora infestans (Mont.) de Bary) and brown rot/bacterial wilt (caused by the bacterium Ralstonia solanacearum (Smith) Smith). Eradication of S. dulcamara has been attempted as a control of brown rot (Persson 1998), and use of water from ditches in which S. dulcamara grows is a known cause of brown rot spread in irrigated potato fields. The role of S. dulcamara in the spread of late blight, however, has been shown to be minimal (Golas et al. 2010b), as most plants are resistant, and those that are susceptible to the disease do not harbour it over winter. Even in very favourable conditions only sporadic infections occur (Cooke et al. 2002; Flier et al. 2003; Dandurand et al. 2006). Solanum dulcamara has novel genes for resistance to late blight, and there is scope for its use in new potato breeding programs in Europe (Golas et al. 2010b). Little work has been done to investigate the mechanisms or genetics of resistance to the major diseases of potato in species outside the Potato clade, but new breeding methods have stimulated the investigation of disease in wild species such as S. dulcamara (Golas et al. 2010b) and S. nigrum L., a European hexaploid member of the Morelloid clade (Lebecka 2008, 2009).

Typification of the many synonyms of S. dulcamara has been very difficult. Many of the early names are found in early 19th century floristic accounts, and while validly and effectively published, usually do not cite specimens. I suspect many of these were not necessarily based on specimens, but rather on field observations. I have not neotypified any of the synonyms for which I could not find specimens directly linked to the original description. In addition, many of the European floras coined complex series of replacement names in the early parts of the 19th century, before the codes of nomenclature became firmly established. Where I have been able to trace the identity and derivation of epithets at varying ranks through citation of specimens I recognised these names as homotypic, but for many of the early names (e.g., those coined by George Don in 1838) the links are very tenuous and I have thus recognised them as heterotypic (and often have not designated types).

The type of S. persicum was a Pallas specimen held in Berlin, now destroyed. A Pallas specimen in BM that matches the description perfectly has been selected as a neotype, although it may not be a duplicate of the original.

The many varietal names coined by George Don (1838) were based not on specimens, but on literature references (e.g., var. album) or personal observations (var. hirsutum). His var. hirsutum referred to plants that were “Hairy or downy. .. On the sea coast”, with no specimens or plates cited. I have not neotypified this name. Varieties album, violaceum and plenum were based on one plate (plate 46) in Hortus Eystettensis (Besler 1613) which is composed of three plants (see Figure 37): one white-flowered S. dulcamara that I have designated as the lectotype of var. album, one violet flowered S. dulcamara that I have designated the lectotype of var. violaceum, and a central plant, used by Don as the basis for var. plenum, that is a drawing of Nigella sativa L. (Ranunculaceae) (see Figure 37). He cannot have been looking very carefully!

Petermann (1838) coined several new infraspecific taxa in his local flora of the Leipzig region; I have found no material related to these names. Solanum maximowiczii was based on “Solanum dulcamara var. ovatum Maxim.” and was coined at the specific level to represent that variety. In his discussion of Solanum dulcamara, however, Maximowicz (Regel and Maximowicz 1870) refered explicity to Dunal’s variety ovatum and did not coin a new name. Thus, this specific epithet is homotypic with the chain of epithets linked to the variety ovatum treated by Maximowicz, ultimately traceable to the (presumably) first instance of this varietal name being used in Petermann’s floristic treatment (Petermann 1838). Dunal (1852), cited by Maximowicz, cites Opiz (Berchtold and Opiz 1843) and Opiz cites Petermann as the origin of the varietal name. I have found no specimens associated with these names.

Dunal’s (1852) treatment of S. dulcamara for the Prodromus has a broad range of variation recognised as a single taxon; he recognised 14 infraspecific entities at two levels, mostly based on literature citations, his final words in the description - “Multum variat.” - couldn’t be more true. He recognised as A, B and C forms previously recognised by Opiz (Berchtold and Opiz 1843) and Petermann (1838) – cordatum, ovatum and hastaefolia. Below them on the page he recognised a series of 11 taxa (“Hae tres formae vicissum variant”) that he listed with Greek letters (α to ξ, leaving out ι, κ and λ), some of which had binomial and others polynomial epithets. Infraspecific taxa denominated with Greek letters in Dunal (1852) have always been recognised at the varietal rank, and no where else in the treatment of Solanum in the Prodromus does Dunal use an apparently nested set of ranks as he does with S. dulcamara. I am therefore assuming that he intended his A, B and C ranks to be hierarchically above the varietal epithets and have treated them as subspecies in the synonymy. It is possible that var. hastiifolia of Opiz is in fact an illegitimate name for var. flexuosa, as it seems from the text that Opiz (Berchtold and Opiz 1843) treated this variety as the typical one, but I cannot be certain and so have recognised it as legitimate. The polynomial varietal epithets (e.g., “corollis violaceis”, “corollis albis”, “corollis carneis”, “flore pleno”, corollis variegatis”) are not legitimate names; I have lectotypified the rest based on either herbarium material or literature citations cited by Dunal. For var. laciniatum, Dunal cited specimens in both P and G-DC; I have found only the G-DC sheet, so have selected it as the lectotype.

The holotype of S. dulcamara var. subglabrum was destroyed in Berlin and a duplicate of Kuntze’s collection held in NY has been selected as the lectotype.

In describing S. dulcamara var. macrocarpum, Maximowicz (Regel and Maximowicz 1870) cites as a locality “Circa Hakodate insulae Jezo pluribus locis”. Several collections of Maximowicz’s from Hakodate dated 1861 are held at LE; others are in BM, GH and NY. It is very unclear whether any of these are true duplicates, so I have selected one of the flowering and fruiting sheets at LE as the lectotype and another at LE that is almost identical in morphology as a possible isolectotype.

Wasibecker’s (1895) S. rupestre is a later homonym of S. rupestre H.W.Schmidt. It is possible that the name Solanum serpentini Borbas & Waisb., apparently coined in 1897 (Soó 1968: 153) is a replacement name for the homonym, as the epithet indicates an origin on serpentine soils (like the type of S. rupestre Waisb.). I have been unable to locate the place of publication of S. serpentini, and so treat S. rupestre Waisb. as a synonym of S. dulcamara and S. serpentini as a doubtful name (see Doubtful and Excluded Names and Names not Validly Published).

Máthé (1972) undertook an exhaustive study of the variation of S. dulcamara in Hungary and described two new variants, one at the form level (forma lucidum) and the other (luc. atroviolaceum) at the rank ‘lucus’ that was used in by Hungarian botanists between variety and forma. He followed Soó (1968) who transfered many earlier epithets to the rank of lucus, however, none of these are validly published, as no explicit reference to the basionym’s place of publication was made as is required by the Code.