Solanum dulcamara L., Bittersweet
Account Summary
Native, locally frequent to quite common. Eurasian southern-temperate.
1860; Smith, T.O.; Co Fermanagh.
April to November.
Growth form and preferred habitats
A climbing or scrambling rhizomatous perennial liana with stems up to 6 m or more in length, but often only half this, and woody at least at the base. The alternate, stalked leaves are of two types: lower leaves are deeply 3-lobed, a large ovate middle and two small side lobes; upper leaves are simple, ovate, cordate at their base, with margins entire. In summer, the stems bear star-like flowers of a bright purple hue with a projecting and strongly contrasting yellow anther cone, making Bittersweet or Woody Nightshade quite conspicuous, distinctive and readily recorded (McClintock 1965).
Typically, Bittersweet occurs in shaded, lowland, marshy ground, including tall herb fens on lakeshores, along riverbanks, stream-sides, plus on damper woodland margins and in hedgerows, thickets and waste ground. S. dulcamara can grow under a rather wide range of lowland, environmental conditions, including in relatively dry and fully exposed sites, but it thrives in damp to wet, semi-shaded, fertile habitats. Under these circumstances it can clamber over and occasionally dominate other herbaceous plants in woodland (Pegtel 1985). A very distinct succulent, prostrate form of the species, var. marinum, grows on maritime shingle (Sell & Murrell 2009).
The established strategy of the species is categorized as intermediate between the generalist C-S-R (ie Competitor/Stress-tolerator/Ruderal) and Competitor. In the herb layer, under woodland shade, it can clamber over and dominate other herbs, but in unshaded habitats it may itself be suppressed by taller-growing herbaceous species (Grime et al. 1988, 2007).
Vegetative reproduction
The plant is long-lived, individuals persisting for c 20 years (Salisbury 1942). It is therefore capable of forming large clonal patches, since when stems touch the ground, or when they fragment and disperse, they can readily root and establish new plants. Fresh shoots can also arise directly from the roots and the creeping rhizome (Salisbury 1964). The frequency of S. dulcamara along stream and river banks may well reflect the ability of the plant to fragment and re-establish new colonies downstream (Grime et al. 1988, 2007).
Flowering reproduction
Flowers are borne in a much-branched, flat-topped inflorescence generally containing around 15 flowers, although there can be up to 25 or more (Tutin et al. 1972). Technically, the inflorescence type is described as a corymbose dichasial cyme! The star-like corolla is 15 mm in diameter, dark purple (rarely white), with five lobes bent backwards, each petal having two greenish spots at the base. S. dulcamara flowers all summer from June to September and fruits from August onwards until the first frost.
The flowers offer visitors plenty of protein and mineral-rich pollen but no nectar and they are adapted to 'buzz pollination' by bumblebees. The bees hang on to the anther cone and vibrate it with their thoracic muscles, releasing the very small pollen grains through apical pores on the anthers (Proctor et al. 1996).
The fruit cluster consists of 6-8 mm, many-seeded, oval, green berries that become bright shiny red when mature. The fruit stalks recurve as the berries develop, finally hanging downwards. Reproductive performance data were calculated by Salisbury (1942, p. 79) from a small sample of eight plants, but he was able to show that the seed output is potentially enormous: the average plant produced around 1,400 berries, each typically containing 38 kidney-shaped seeds, so that the annual seed total per plant lies somewhere between 40,000 and 70,000!
Berries are produced from late July onwards and while those formed in relatively dry, exposed conditions may shrivel after only a month, plants in more typical damp, sheltered habitats can carry fruit in good condition until December, long after the leaves have fallen. A range of birds eat the berries and disperse the seed. Chief amongst these are Blackcaps, Blackbirds, Song Thrush, Robin and Starling. A certain amount of seed predation has been observed, the main culprits being Bullfinches (Snow & Snow 1988).
Seed requires low temperature after-ripening, or a period of natural weathering involving fluctuating temperature. Germination occurs in the spring (Pegtel 1985). Little or no persistent seed bank exists (Grime et al. 1981; Roberts 1986). Despite the considerable range of variation found in the species and its wide ecological tolerance, Pegtel (1985) could not detect genetic differences in the germination of seed from contrasting habitats and the case for delimiting ecotypes does not seem convincing.
Fermanagh occurrence

In Fermanagh, the plant is really rather local, but very frequent where it does occur, particularly around both parts of Lough Erne as the tetrad map indicates. It has been recorded in 119 tetrads, representing 22.5% of those in the VC. All but seven of the tetrads contain post-1975 records. A total of 90 tetrads are concentrated in and around Lough Erne.
British and Irish occurrence
In Britain, S. dulcamara is widespread and common in England and Wales, but is absent from land lying above 310 m (ie around 1,000 ft.). It becomes rare and more or less coastal in N England and Scotland. In Ireland, S. dulcamara is much more frequent in the N & E of the island, stretching as far south as Dublin. However, it becomes scarce to rare in the far W & SW of the RoI (Rich & Woodruff 1990; An Irish Flora 1996; New Atlas).
There did not appear to be any appreciable change in the presence of S. dulcamara from the evidence contained in the BSBI Atlas 2000 survey (T.D. Dines, in: Preston et al. 2002), but the subsequent second monitoring survey also carried out by the BSBI in Great Britain only, Change in the British Flora 1987-2004 found a definite and statistically significant decline with a 'Change Factor' measuring -11 (Braithwaite et al. 2006).
European and world occurrence
S. dulcamara belongs to the Eurasian southern-temperate phytogeographic element and is widespread throughout most of Europe and Asia except the extreme north with the native range extending into N Africa and the Middle East. It has been introduced to N America (Hultén & Fries 1986, Map 1624; Grime et al. 1988, 2007).
Toxicity
All parts of the Bittersweet plant contain a mixture of steroidal glycol-alkaloids often referred to collectively as 'solanine'. The alkaloids are degraded during the maturation of the fleshy fruit. It is suggested that this makes the berries more attractive food for birds and other animals that eat them and transport the seeds in their gut. The ripe berries should not, however, be regarded as safe to consume as they have been known to cause poisoning (Cooper & Johnson 1998).
In the 1960s and early 1970s, poultry and sheep are known to have died after grazing the plant and children who ate the attractive-looking berries were very sick, although thankfully only one of them died (Cooper & Johnson 1998)
Uses
S. dulcamara has a history of use in herbal medicine dating back to classical times and there are few ailments and complaints for which it has not at some time been recommended. The main uses were in treating rheumatism, skin diseases and as a purgative. Gerard (English), Boerhaave (Dutch) and Linnaeus (Swedish) all spoke highly of its medicinal virtue and S. dulcamara continued to feature in the British Pharmacopoeia until 1907 for skin complaints, after which it was dropped from modern pharmacy (Grieve 1931).
N.B. No part of the plant should ever be eaten, as even the ripe black berries may contain the very poisonous alkaloid, solanine.
Names
The name 'Bittersweet' was coined by the 16th century English herbalist, William Turner, who translated the medieval Latin names for the plant, 'dulcamarum', 'dulcis amara', or 'amara dulcis' (dulcis, sweet and amarus, bitter), referring to the woody stem bark, which if tasted is at first sweet and then turns very bitter in the mouth (Britten & Holland 1886; Grigson 1974). The modern botanical species name 'dulcamara' given by Linnaeus refers to the taste change more correctly. Do not attempt to test this taste change, for fear of dangerous ill effects! The medieval herbalists also referred to S. dulcamara as 'Woody Nightshade' to distinguish it from its relative, 'Deadly Nightshade' (Atropa belladonna).
There are numerous alternative, local English common names. Grigson (1955, 1987) lists a total of 22, six of which refer to the plant's poisonous nature. Numerous other names refer to supposed magical properties that garlands of the plant, on account of its red berries, offered against witches and sudden illness.
Threats
None.