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Solanum nigrum L., Black Nightshade

Account Summary

Introduction, possibly an archaeophyte, but only a very rare casual. As a native, it appears Eurasian temperate, but it is also very widely naturalised.

29 July 1986; Corbett, P., Austin, L.W. & Wolfe-Murphy, S.A.; waste ground on S section of Corrard shore, Upper Lough Erne.

July and August.

Growth form and preferred habitats

S. nigrum is a white-flowered, rather hairy, much branched annual, or short-lived, monocarpic perennial with fibrous roots and oval leaves. It is sometimes quite woody at the base. It is a rare, occasionally abundant, casual alien in Ireland, where it most often occurs in cultivated ground, gardens, waste ground, at ports and among suburban planted shrubs, along with which it may have been introduced (Cat Alien Pl Ir). It mainly occurs in southern VCs (Cen Cat Fl Ir 2). Black Nightshade is also called Garden Nightshade, since it is a notorious garden weed of fertile, nitrogen- and phosphorus-rich soil, manure heaps and on waste ground where there is organic enrichment (Garrard & Streeter 1983). It prefers moist environments and thrives in regions with low rainfall only where there is irrigation (Holm et al. 1977). Although often low and spreading (10-30 cm), S. nigrum can grow 60-100 cm tall. In flower, it bears small, ivory-white, star-like flowers in clusters of 3-12 (but usually numbers 7-9) (Salisbury 1964; Sell & Murrell 2009).

In terms of established strategy, S. nigrum is classed as an R/CR, ie intermediate between Ruderal and Competitive Ruderal (Grime et al. 1988, 2007).

Variation

S. nigrum is a very variable species both in terms of physical or geographical forms and its physiology. So much variation is involved that it is probably best to consider S. nigrum as a complex of subspecies, varieties and forms with varying degrees of similarity, rather than as a single, clearly defined species (Cooper & Johnson 1998). In the critical Flora of B & I, Sell & Murrell (2009) describe two subspecies (subsp. nigrum and subsp. schultesii (Opiz) Wessely), plus three varieties of the former.

When taken in the broad sense as the S. nigrum species complex, the plant has an almost world-wide distribution as an arable weed. It is reported as an important weed in 61 countries and 37 crops (Holm et al. 1977). Even when considered in the more restricted Eurasian form of the species, it is morphologically and physiologically variable in different locations and between populations, some of which are in the process of developing resistance to herbicides (Cooper & Johnson 1998).

Fermanagh occurrence

This is a very rare plant in Fermanagh, there being records from a total of only five sites in separate tetrads. The details of the earliest two Fermanagh records, both from around Upper Lough Erne, are firstly as given above and, secondly, waste ground at Killynubber Lough, 15 August 1986, L.W. Austin & S.A. Wolfe-Murphy. The recorders of the first Fermanagh record, however, questioned its occurrence at the time. Consequently, both it and the subsequent Killynubber record require further verification. Regrettably, since there are no voucher specimens for either discovery, they fail to fit the BSBI criteria for first and second county records and, strictly speaking, they are unacceptable. On the other hand, Black Nightshade is easily recognised, its stem being entirely herbaceous, up to 60 cm tall, the leaves oval, sometimes deeply toothed and the flowers are familiar and potato-like. Thus it is very likely that the two Fermanagh identifications were perfectly correct.

The details of the remaining three sites are: in hedge at Knockninny Quarry, 29 August 2004, I. Rippey; Killymackan Lough ASSI, 24 June 2007, ENSIS Lake Survey; Galloon Td, Upper Lough Erne, 17 August 2006, ENSIS Lake Survey. Again, the database does not mention vouchers for these sites.

Fossil history, species status and occurrence in Britain

Despite its weedy behaviour and the wide range of variation mentioned above, appropriate fossils (seed from the Cromerian and pollen from the Flandrian interglacial periods) prove S. nigrum is undoubtedly of early native status in SE Britain, if not too likely so in the rest of Britain, or in Ireland (Godwin 1975). Having said this, there are two mediaeval fossil records from Ireland, and the two earliest Flandrian records in England lie near the presumed northern limit of its range (Godwin 1975). Later fossil records from the Roman and mediaeval periods confirm S. nigrum's association with cultivation and with other weedy species (Godwin 1975).

S. nigrum is widespread and common in England and parts of Wales, S & E of a line from the Humber to the Severn, but it is scarce elsewhere in Wales and in SW England and absent or purely a casual alien in both Scotland and Ireland (Garrard & Streeter 1983; T.D. Dines, in: Preston et al. 2002).

Irish occurrence

In NI, until recent years, S. nigrum had only been recorded on a total of five occasions in Cos Down (H38) and Antrim (H39) during the pre-1925 period (FNEI 3). With the increased recording effort associated with a flora survey of urban Belfast in the 1993-5 period and the subsequent wide-ranging BSBI New Atlas 2000 survey, a total of twelve more records were discovered; three records each in Cos Antrim, Down and Tyrone (H36), plus one in Co Armagh (H37) and the two in Fermanagh (H33) already mentioned. Since the New Atlas was published in 2002, two additional Tyrone records have been listed by McNeill (2010), one of them from a maize crop. Interestingly, S. nigrum was discovered for the first time between September 1998 and 2000 in Co Cavan (H30) (which shares a border with Fermanagh), at no less than five different sites (Reilly 2001).

Elsewhere in the RoI, S. nigrum is very thinly and widely scattered, with a cluster of hectads around Dublin (H21) and Wexford (H12) (New Atlas). In Co Waterford (H6), S. nigrum appears to be increasing in recent decades; although still a casual ruderal of open habitats, it also appears as an arable weed of sugar beet, maize and carrot crops (Green 2008).

Flowering reproduction

S. nigrum relies entirely on seed reproduction for increase, dispersal and survival. Seeds germinate in the spring, from early May onwards, reaching a peak emergence in late May or June (Roberts & Lockett 1978). Plants reach flowering condition from July to September, the regular (actinomorphic), perfect (bisexual), star-like flowers, 10-14 mm in diameter have a calyx of five erect, fused, oblong sepals, not enlarging in fruit. The five ivory-white, fused petals are about twice as long as the calyx, the lobes spreading at first, then rolling back on themselves (ie revolute) as the flowers age. The long, bright yellow anthers are inserted (ie attached) on very short filaments to the corolla tube, so that they poke out of the corolla. They lie close to one another, forming a cone around the long, well exerted, solitary style and stigma.

The anthers open through pores at their tips to release the pollen that is the main flower food attractant, since the very little nectar is produced. Insect visitors (mainly bees) cling to the cone of anthers and by vibrating their wings rapidly, they draw pollen out through the anther pores onto their hairy bodies. Since the style protrudes well beyond the anther cone, the stigma tends to be cross-pollinated (Proctor & Yeo 1973; Hickey & King 1981).

Fruit and seed production

Fruits ripen in succession from September to November if the weather remains mild. The plant is killed, however, by the first frosts. The plant produces globular fleshy berries, green at first, then turning shiny, black when ripe, 5-13 mm diameter, with the slightly enlarged sepals attached, curving backwards. The fruits are more watery than fleshy and they do not persist for long if not eaten: they tend to burst open and then dry out (Snow & Snow 1988). Each fruit contains 40-50 flattened seeds which can pass unharmed through the digestive tract of farm stock and other animals. The average number of fruit per plant measured by Salisbury (1942) was 238, so it is very possible that an average-sized individual plant could produce around 9,500 seeds. In the same study some really huge plants were calculated capable of producing up to 130,000 seeds (Salisbury 1942). A maximum seed number of 178,000 per plant was published by Holm et al. 1977).

Seed dispersal

Birds are undoubtedly one of the main vectors of S. nigrum seed. Studies using marked berries showed that birds took ripe berries during the second half of September and in October. Blackbirds and Robins are the species most involved, with Starlings the third possibility (Snow & Snow 1988). Observation suggests that storm rain-wash along paths and bare ground is another short-range method of S. nigrum dispersal (Ridley 1930). Probably man has become the most significant vector of all, since in historic times, S. nigrum has been introduced with crop seed worldwide and has become one of the most noxious alien weeds in many countries (Ridley 1930; Holm et al. 1977).

Seed longevity

Establishment after dispersal is assisted by the relatively long survival in soil of undisturbed buried seed. Roberts & Lockett (1978) reported survival rates akin to those of Capsella bursa-pastoris (Shepherd's-purse), Chenopodium album (Fat-hen) and Poa annua (Annual Meadow-grass); in the long-running Duvel experiment (Toole & Brown 1946), seeds placed at depths of 20, 56 and 107 cm showed little loss of viability after 39 years.

European and world occurrence

The black-fruited, rarely green-fruited S. nigrum s.s. is believed to have originated in S & C Europe and is distributed throughout most of Eurasia including N Africa and stretches eastwards to the Yenisej River and C Asia. It has been spread with agriculture and is commonly introduced in E Asia and from Nova Scotia to Florida and westwards in America, although mostly along the Atlantic seaboard (Hultén 1971, Map 258; Hultén & Fries 1986, Map 1622; Clapham et al. 1987).

The species s.l. (including S. americanum Mill. and other different but very closely related taxa) is almost cosmopolitan, occurring throughout Europe, Asia, N, C & S America and the tropics of both the old and new world. In many areas of Europe, Asia and N America, both native and introduced taxa within the S. nigrum complex are present. The distribution of the S. nigrum complex is discontinuous circumpolar and it has been introduced to many isolated islands around the world, including Cape Verde Islands, Réunion, Madagascar, Australia, New Zealand, Tasmania and Hawaii (Hultén 1971; Hultén & Fries 1986).

Toxicity

All parts of Black Nightshade plants, but particularly the green unripe berries contain amounts of the poisonous steroidal glycoalkaloid, Solanine. Nitrates and nitrites also occur in variable amounts and can contribute to the toxic effects of the plant. Ripe, shiny black berries are the least poisonous parts of the plant, the poisonous principle being chiefly associated with all green parts (Grieve 1931; Cooper & Johnson 1998). Although the amount of toxin varies with growing conditions and plant age, Black Nightshade should be considered dangerously poisonous to all farm stock and to humans. Cattle will not eat the plant and sheep rarely do (Grieve 1931).

Names

The name 'Solanum' is a classical name, first given by the Roman naturalist Pliny to one of the Nightshade species. It possibly may be derived from the Latin 'solamen', meaning a solace, referring to its supposed medicinal virtues (Johnson & Smith 1931). On account of its shiny black berries, S. nigrum was called by older herbalists 'Petty Morel' to distinguish it from its even more dangerously poisonous relative, 'Deadly Nightshade' (Atropa belladonna), often known as 'Great Morel'. The dried whole plant or fresh leaves are (or were) used in herbal medicine. Black Nightshade has narcotic properties and is a strong sudorific (ie it causes sweating).

The chief uses are in treating skin diseases, for instance, dealing with obstinate skin eruptions, burns and ulcers using bruised fresh leaves externally to ease pain and abate inflammation. However the action is variable and even the herbalists considered it a rather dangerous remedy, except when used in small doses. There are reports of the leaves being eaten like spinach and of it being a famine food, but this should never be countenanced (Grieve 1931).

Threats

None.