Traits of Weed Archetypes

Black nightshade, Solanum nigrum

  Alireza Taab

  Agron517 March 2007


S. nigrum is reported as a weed of over 37 crops in 61 countries around the world. It is a common weed of many fruits, vegetables, crops, waste area, and open forest. It is a native of Europe. It is also an alternate host of some important fungi, nematode, and virus diseases (Holm et al. 1991).

S. nigrum  is an erect to spreading, 15- to 100-cm tall, branching, annual to short-lived perennial herb to subshrub. Roots are mainly fibrous with a shallow taproot. Stems are round to angular and covered with curved multicellular hairs sometimes tipped with a glandular head. Simple leaves are 2 to 8 cm long by 1 to 5.5 cm wide, ovate or ovate-lanceolate to lanceolate in shape with wavy-toothed margins. Inflorescences are simple, with pedicels closely clustered and forming an extended cyme or raceme-like cluster of 2 to 10 flowers. Flowers are 4 to 18 mm in diameter and bell-shaped, with a star-shaped, white corolla with a translucent to yellowish basal star. The calyx consists of ovate sepal lobes that are 1.2 to 2.5 mm long and a star-shaped corolla of five white lobes that are 1.8 to 7.5 mm long. Fruit are broadly ovoid and have dull purple to black or yellowish-green berries that are 6 to 10 mm broad. Berries may remain on the plant or fall to the ground when ripe. Fruit are without sclerotic granules on the surface. Seeds are tan, obovate, flat in cross-section, 1.7 to 2.4 mm long (Defelice, 2003).

There is a taxonomic confusion surrounding S. nigrum and its component species (Edmonds & Chweya 1997), presumably because of the historical factors, phenotypic plasticity, genetic variation, the existence of a polyploid series, and the possibilities of interspecific hybridization (Edmonds, 1977). Therefore, the information about this species has to be interpreted with caution.

The section Solanum, centering around S. nigrum L., is one of the largest and most variable species groups of the genus. Species belonging to this section are distributed from temperate to tropical regions, and from sea level to altitudes over 3500 meters. Though this species group is often referred to as the Solanum nigrum complex, the section is composed of a large number of morphogenetically distinct taxa, which show their greatest diversity (Edmonds & Chweya 1997). The majority of the diagnostic characters, which have been used by some authors to identify the species belonging to the section Solanum, are extremely variable as well as some species are more variable morphologically within this section (Edmonds, 1986).

According to Edmonds & Chweya (1997) S. nigrum L. has two subspecies:

S. nigrum L. subsp. nigrum,

S. nigrum L. subsp. schultesii (Opiz) Wess.

Chromosome no. (2n=72)

The key to differentiate between two subspecies:

S. nigrum subsp. nigrum;

Plants subglabrous to pubescent usually with appressed, eglandular-headed

multicellular hairs

S. nigrum subsp. schultesii;

Plants villous, usually with patent, glandular-headed multicellular hairs

  Cytology: 2n=6x=72 (Edmonds 1977)


Harmful properties

S. nigrum is one of the worst world’s weeds (Holm et al., 1991) and it cause not only crop yield losses through competition for recourses, but also cause reduction of crop quality by contaminating crops such as peas, beans and soybean (Edmonds & Chweya, 1997; Defelice, 2003). It also host insects, nematodes, and disease organism that attack crops (Ogg & Rogers, 1989). Members of Solanaceae contain a toxic glycoalkaloid called solanine. The amount of this toxin varies with the species, environment, part of the plant, and stage of growth (Defelice, 2003), genetic races, soil factors, management practice, and climate conditions (Ogg & Rogers, 1989). The highest concentrations of solanine in S. nigrum are in the immature fruits (Defelice, 2003). The unripe green berries may inadvertently pick up and mix with crop i.e. peas. The allelopathic inhibitory effect of extracts from S. nigrum on chickpea seed germination has been noted (Kadioglu et al., 2005). 


Beneficial properties

S. nigrum is considered as a medicinal plant, source of food, indigenous plant genetic resource in many countries (Ogg & Rogers, 1989; Holm et al. 1991; Agong, 1993; Edmonds & Chweya, 1997; Defelice, 2003).  It’s also used as the painkiller (Zubida et al., 2004). An isolated glycoprotein from S. nigrum has been identified as a natural anti-cancer agent (Lim, 2005). Zakaria et al., (2006) demonstrated that the lipid-soluble extract of S. nigrum leaves possessed antinociceptive, anti-inflammatory and anti-pyretic properties.



Solanum nigrum is mainly a weed of moist environment, and thrives in areas of low rainfall only where the land is under irrigation. It is best adapted to soils of high fertility, especially those high in nitrogen and phosphorus. It has been naturalized in both temperate and tropical regions (Holm et al. 1991). This species colonize moist environments, only occurring in areas of low rainfall when the land is subject to irrigation. However, it is susceptible to frost (Edmonds & Chweya 1997).


Traits of the species


Seed Production

The potential of seed production in S. nigrum vary in a range of 600 to 168000 seeds per plant (Keeley & Thullen, 1983; Holm et al. 1991; Defelice 2003).  Each berry contains 15 to 96 bone-coloured seeds (Ogg & Rogers, 1989; Defelice, 2003). 


Seed Longevity

Long survival of dormant seeds enables a plant population to build up a bank of seeds of different ages in the soil (Håkanson 2003). Seeds of S. nigrum can remain viable in the soil for a long time (Ogg & Rogers, 1989; Keeley & Thullen, 1989). Viability of S. nigrum seeds in the soil has been reported from 18 to 39 years depending on soil disturbance. Tillage can decline number of seeds exponentially over years (Ogg & Rogers, 1989; Defelice 2003). However, appreciable numbers of viable seeds survive in the field for 5 years (Roberts & Lockett 1978). Keeley & Thullen (1989) indicated that S. nigrum seed survival in soil appears to be long. Thus, fields should be kept weed-free for more than 5 years to reduce S. nigrum populations to a level that will not reduce cotton yields. Also, S. nigrum seeds remain viable after being eaten by birds and livestock (Roberts & Lockett 1978; Defelice, 2003).


Seed Dispersal

S. nigrum seed dispersal is through contaminated agricultural products or by birds and animals who eat the succulent berries (Roberts & Lockett 1978; Edmonds & Chweya 1997; Defelice, 2003). Also, it has been suggested that migratory birds may have played an important role in spreading seeds of S. nigrum resistant to triazines in Europe (Stankiewicz et al. 2001).



Seed Dormancy and Germination

Seed dormancy of S. nigrum has been recognized as non-deep physiological dormancy (Baskin & Baskin, 1998). The breakage of dormancy occurs increasingly in seed stratified in low temperatures up to 15 ºC and a breakpoint is between 15 and 18 C, where phases of dormancy breakage and induction meet as a result of stratification duration (Taab, 2007). In general, freshly harvested S. nigrum seeds have little or no dormancy and germinate within a few weeks of separation from the berry (Keeley & Thullen, 1983; Ogg & Rogers, 1989; Robert and Locket, 1978; Defelice 2003). However, a study on primary seed dormancy of S. nigrum showed differences between populations and date of collection. A substantial germination occurred only in germination condition test in light indicating light requirement for terminating seed dormancy in this species. Also, the light requirements for germination could be decreased by prolonged cold stratification (Taab, 2007). The changes in seed dormancy of S. nigrum follow a seasonal pattern. The cold temperatures during autumn, winter and spring break seed dormancy and warm temperatures during summer cause induction of dormancy in this species, showing characteristics of summer annual behavior (Taab & Andersson, 2007; Roberts and Lockett, 1978).

S. nigrum seeds can germinate over a very wide period in spring and summer (Defelice, 2003). Both buried and freshly harvested seeds of S. nigrum cannot germinate at constant temperatures in the range of 4-30ºC with intermittent exposure to light, but alternating temperatures cause complete or almost complete germination (Roberts and Lockett, 1978). Similarly, Wagenvoort & Van Opstal (1979) showed that an alternating temperature is necessary for seed germination of S. nigrum, and the germination percentage is also improved by a cold pre-treatment. Del Monte & Tarqius (1997) reported that the optimum temperature for germination of S. nigrum populations is between 20ºC to 30ºC and there are differences in base temperature for germination between populations from 7.5ºC to 10ºC. However the S. nigrum seed seems to germinate best at alternating temperature of 20 to 39 ºC (Holm et al. 1991).



S. nigrum prone to late germination mainly in late spring (Håkanson 2003). Seedling emergence in S. nigrum begins in early May, continued during June and July, tail off during August and cease in September in U.K. (Roberts and Lockett, 1978). A study by Ogg & Dawson (1984) in USA showed that S. nigrum generally began to emerge during the first 2 weeks of April and emergence generally peaked in mid-April to mid-May and continued until September. Also, shallow tillage at monthly intervals increased the overall its emergence. Keeley & Thullen (1983) stated that S. nigrum seeds begin to emerge in March in California when soil temperature at 5 cm depth reached 17 ºC.  Though differences has been observed between populations S. nigrum seedling emergence starts in May and seized in early July in Sweden. Seedling emerged in late spring have enough time to complete their life cycle and induction of seed dormancy during summer inhibits late germination and subsequent plant death in autumn (Taab, 2007). Therefore, the comparatively late emergence contributes to the seriousness of the species as a weed of various vegetable and arable farm crops, since it often take place after contact herbicides have been applied and when the activity of soil-applied treatments has declined (Roberts and Lockett, 1978).

Kremer and Lotz (1998) reported significant differences between triazine resistant and susceptible S. nigrum biotypes in emergence fractions. Resistant seeds showed a higher emergence fraction than susceptible seeds. Solanum nigrum seedlings resistant to triazine herbicides emerged faster and in greater proportion than triazine-susceptible seedlings, because of the interaction between soil temperature and differential minimum germination requirements of seeds between the biotypes (Kremer and Lotz, 1998). S. nigrum seeds seem to emerge from a depth of 2.5 (Keeley & Thullen 1983), 4 (Kremer and Lotz 1998) up to 8 cm (Benvenuti et al., 2001) depending on type of soil. 


Vegetative growth

Black nightshade is sensitive to shading and crop competition and its growth and seed production is severely decreased under shade (Holm et al., 1991). S. nigrum plant that germinated from March through June began flowering 7 to 9 weeks after planting, whereas plant germinating from July through September flowered after 5 to 6 weeks. Plants germinating in October were killed by frost in November. Plant growth was more rapid for plant that germinated from May through July (Keeley & Thullen, 1983). González-Ponce et al. (1996) observed that S. nigrum competes strongly for light, reducing the effective photosynthetically active radiation (PAR) that reaches the lower species, i.e. the pepper with a slower initial growth. McGiffen et al. (1992) reported that height was a major factor in competition between tomato and black nightshade. Black nightshade competition for light and nutrients with tomato was greater when black nightshade was taller than tomato at flower initiation (González-Ponce et al. 1996), which typically occurs when both plants emerge at the same time. S. nigrum plants that emerge late spring in Iran under rather dense crop canopy can produce few berries, which is enough to guarantee future infestation (personal observations).

The leaf margins may vary from entire to sinuate-dentate in different populations of S. nigrum, while different indumentum types characterize the different subspecies. S. nigrum also display a range of berry colours within its subspecies varying from green through purple to black (Edmonds & Chweya 1997).


Genetic variation

Many species in section Solanum exhibit considerable genetic variation, both florally and vegetatively. This variation may occur in different populations of the same species, or may characterize different infraspecific categories of a species. Sometimes, the character may be genetically controlled in one species, but phenotypically plastic in another. (Edmonds & Chweya 1997).



Species belonging to the section Solanum constitute a polyploid series, with diploid (2n=2x=24), tetraploid (2n=4x=48) and hexaploid (2n=6x=72) species occurring throughout most of the geographical range in which the section is found. Octoploid plants (2n=8x=96) also have been reported (Edmonds & Chweya 1997). S. nigrum is a hexaploid plant (Edmonds & Chweya 1997;  Edmonds 1977).


Reproduction and natural hybridization

Sexual fertilization leads to seed production in S. nigrum.

Species belonging to the section Solanum are predominantly self-pollinating, but out- and crossbreeding can occur as well as natural inter- and infraspecific hybridizations. Natural hybrids also have been reported at higher ploidy levels, e.g. infraspecific hybrids of the hexaploid S.nigrum and interspecific hybridization with other species with different ploidy level  (Edmonds & Chweya 1997).


Herbicide resistance

Some biotypes of S. nigrum have been reported to be resistant to herbicides belong to the Photosystem II inhibitors including atrazine, cyanazine, prometryn, and terbuthylazine and they may be cross-resistant to other herbicides within this group.

Researchers have indicated that resistant S. nigrum is ecologically less fit than normal susceptible one.  Triazine resistant weeds often exhibit a lower relative fitness when compared to susceptible biotypes.  The most common mutation conferring triazine resistance also causes a reduction in CO2 fixation, quantum yield, and seed and biomass production (, online). Kremer & Kropff (1998) showed that the final total dry matter production and berry production of the triazine-resistant biotype of S. nigrum are lower than those of the susceptible biotype. 


Seed Reproductive Growth

It seems that most species in the section Solanum to be capable of hybridization, it is probable that complex population variation would occur where their distributions overlap (Edmonds, 1977). Keeley and Thullen (1983) indicated that S. nigrum planted in May through July produced 20000 to 30000 seeds but only 600 to 8000 seeds per plant when planted in March, April or August. In general, S. nigrum thrive very well and produce large number of seeds when there is enough resource available and no serious crop competition (Holm et al., 1991). 


Table of Life History Traits

Life history process

Plant morphological structure

Developmental Process

Whole plant activity-phenotype



Parental Seed


Zygote formation

Dormancy establishment

Seed maturation

Seed production plasticity

Seed dormancy


Independent Seed

Soil seed bank formation

Seasonal dormancy cycle

Dispersal in time and space




Cotyledon and first true leave emergence

Plant establishment

Seed bank formation

Late and extended germination

Vegetative growth

Vegetative plant

Growth and meristem morphogenesis


Rapid growth

Vegetative growth plasticity

Herbicide resistant biotype

Alternate host for crop pest

Seed reproductive growth

Flowering plant

Flower formation

Seed formation


Seed growth

Self-pollination & out and cross breeding


Most important traits

Seed production plasticity; S. nigrum plants tolerate wide range of habitats, able to start flowering in early stage of growth and potentially capable of producing huge number of seeds under favorable growing conditions and few seeds under unfavorable conditions.  

Seed dormancy; S. nigrum seeds go through seasonal dormancy cycle during period of a year. They germinate only when the environmental condition is favorable for germination and its subsequent growth. Therefore, it can build up a seed bank for a long period of time.

Growth habit; although S. nigrum is a late germinating weed, it is able to grow fast and occupy opportunity space between crop stands. It thrives very well when the crop is less competitive or crop canopy is sparse.



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