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Senecio vulgaris L., Groundsel

Account Summary

Native, common and widespread. European southern-temperate, but widely naturalised in both hemispheres and now circumpolar southern-temperate.

1881; Stewart, S.A.; Co Fermanagh.

Throughout the year, populations peaking in August.

Growth form and preferred habitats

S. vulgaris is a shallowly taprooted summer or winter annual, varying from small and very spindly to irregularly branched and bushy in habit, with pinnatifid leaves, the upper ones clasping the stem. The stems are erect, hollow, glabrous, slightly ridged and grow 10-60 cm tall. Groundsel is mainly found in open, ruderal, impermanent, often artificial habitats with bare more or less fertile soil. It colonises any bare ground in cultivated, disturbed, derelict, waste ground and rocky sites, including in gardens, gravel paths and forecourts, along tracks and roadsides, on coastal dunes, shingle, cliffs and on walls. It is interesting that in Canada, where it is an introduction, S. vulgaris is primarily a weed of pastures rather than of field crops (Robinson et al. 2003).

In all of these situations, it can complete its life cycle in a very short period of time (see below). S. vulgaris is easily distinguished from S. sylvaticus (Heath Groundsel) by having well-developed bracteoles (outer bracts) around the flowerhead that are black-tipped. S. sylvaticus also has ray-florets, although they are inconspicuous, the ligulate petals being less than 2 mm in length and revolute (ie they soon turn down) (Robinson et al. 2003; Sell & Murrell 2006).

S. vulgaris is unable to establish in sites that are regularly or very heavily disturbed, whether grazed, mown or trampled. It also cannot tolerate much shade and avoids wetlands and unproductive, infertile and strongly acidic soils below pH 4.5. Having said this, it is remarkably variable and phenotypically plastic, capable of producing dwarfed plants in conditions of nutrient stress and drought that still manage to reproduce, although they often do so to a very limited extent and any seed produced may well prove non-viable (Grime et al. 1988, 2007).

The pale yellow flowerheads are typically composed of 10-20 small, tubular, bisexual, disc-florets and are without ray-florets, although rayed forms do occur, especially in S & W Britain (see below). The flowerheads are bunched in terminal corymbs (Melderis & Bangerter 1955). The species germinates and flowers all year round, overwintering flowering plants being perfectly common throughout B & I (Kadereit 1984; Grime et al. 1988, 2007).

Fermanagh occurrence

In their 1975 unpublished Revised Typescript Flora, Meikle and his co-workers considered Groundsel, "by no means a common plant in the county". While RHN and the current author (RSF) absolutely could not agree with this assessment, S. vulgaris is much less frequent than either S. aquaticus (Marsh Ragwort) or S. jacobaea (Common Ragwort), having been recorded in just 252 tetrads, 47.7% of those in the VC. While widespread throughout Fermanagh, it is less common on higher ground and, as is always the case, it is absent from strongly acidic bogland.

Three forms of S. vulgaris occur in the British Isles (New Flora of the BI 1991) but, so far, S. vulgaris var. vulgaris, the type variety that differs from the other forms in lacking ray-florets, is the only form that has been recorded in Fermanagh.

Another form, S. vulgaris var. hibernicus Syme., is believed to have originated in Ireland in or around Cork city sometime prior to 1853, when a specimen was sent to Prof Babington at Cambridge (CGE) and labelled as, "hybrid between S. vulgaris and S. squalidus". It appears that genes of the latter have introgressed the genome of S. vulgaris to create this variant form (Briggs et al. 1992). Var. hibernicus has been found in Cos Down (H38), Antrim (H39) and Londonderry (H40) and Hackney et al. (1992) suggest that it is increasing in the NE of Ireland. Since it is usually associated with railway tracks or coastal sites, however, it may take some time to reach Fermanagh – where neither of these habitats are available!

Fermanagh has a limited range of annual, ruderal Senecio species and until recently neither S. squalidus (Oxford Ragwort) nor S. viscosus (Sticky Groundsel) had ever been recorded here. Solitary records of both of these weeds were first recorded in the VC in 2000 and 2002 respectively by RHN.

Flowering reproduction

The small, yellow, rayless flowers of S. vulgaris are predominantly self-pollinated, but the extent of this appears to vary in different populations. In areas where radiate flowers occur, the fact that this character is controlled by a single incompletely dominant gene (Trow 1912), has allowed measurement of the degree of out-crossing with non-radiate forms. Heterozygote plants can be clearly distinguished from the homozygous radiate and non-radiate forms by them having rays of intermediate length (Briggs & Block 1992). This shows that rates of out-crossing range from 1.0-22.4%, with insects making more visits to radiate forms, which are naturally more conspicuous. The flowers do offer small amounts of nectar that attracts small insects (Melderis & Bangerter 1955). Warren (1988) used a gene that controls bract colour as a marker and found that non-radiate forms out-crossed at about 17%. Experiments have shown that there is a degree of maternal inheritance in characters, such as those affecting response to soil fertility and the development of herbicide resistance (Briggs & Block 1992).

Groundsel plants have a high relative growth rate and they respond to moderate environmental stress by precocious development, reproducing a few days earlier than they would otherwise (Harper & Ogden 1970). In more severe environments, as in pavement margins, dry gravel, or on walls, plants are typically dwarf and unbranched, flowering and fruiting at about the twelve leaf stage when only 10-15 cm tall. Under such stressed circumstances, the plant may produce only one or a very few flowerheads, and even if it manages to fruit, the seeds may fail to germinate. Whatever the environment, approximately one quarter of the plant's photosynthetic resources are devoted to reproduction (Harper & Ogden 1970).

S. vulgaris is obligately annual and monocarpic. A short life-span of as little as six weeks allows the species to produce up to three generations per year. English waste ground plants examined by Salisbury (1942, 150-151) had an average of 24.7 flowerheads and a mean seed production of 1,127 ± 60/plant. This gave a probable reproductive capacity of over 1,000 seeds/plant since percentage germination is usually about ninety and seed production peaks between May and October (Grime et al. 1988, 2007). On the other hand Harper & Ogden (1970) reckoned that plants in low stress environments, such as garden soil or agricultural land, may bear more than 1,000 capitula. Using Salisbury’s mean of 45 achenes per capitula, groundsel plants with 1,000 flowerheads would produce 45,000 seed. This is compatible with the outcome in plants growing in agricultural fields and roadside areas in NW United States, which gave an average of 38,300 seeds per plant and a maximum of 40,700 (Kempen & Graf 1981).

Seed dispersal

Although the achenes (or seeds) possess a conspicuous plumed pappus and are thus adapted for wind dispersal, the measured mean distance of seed travel is low at 34 cm, with a maximum of around 2 m. It has to be remembered that local topography, and in particular the pattern and scale of vegetation gaps, certainly defines the so-called 'seed shadow' of dispersal around the parent plant (Bergelson et al. 1993). Seed transport may also be assisted to some extent by animals including man, since the pappus hairs are sticky when wetted and may adhere to coats of passing animals. Achenes can also survive passage through birds and cows and be dispersed in their faeces (Ridley 1930), but the worldwide spread of the species has undoubtedly been achieved by human transport of achenes as contaminants of agricultural seed.

Un-germinated seeds have a limited ability to persist in the soil, and the buried seed bank appears to be relatively small at around 590 seeds/m2 or less (Lawson et al. 1992). The survey of soil seed banks in NW Europe contained a total of 37 estimates of which seven considered persistence was transient (ie less than one year), 15 believed it short-term persistent (ie surviving one to five years), six studies regarded it as long-term persistent (ie surviving more than six years) and nine found it was present in soil but could not assign it to one of the other three categories (Thompson et al. 1997).

Rust disease

A rust disease caused by Puccinia lagenophorae Cooke is very common and depresses the reproductive output of the plant (Paul & Ayres 1987). Rust infected plants become weakened and vulnerable and they may be killed by a secondary Botrytis cinerea infection (Hallett et al. 1990).

Toxicity

In common with other Senecio species, Goundsel contains the defensive toxic alkaloids, senecionine, seneciphylline and their N-oxides (Brown & Molyneux 1996). These alkaloids are produced in the roots (Hartmann et al. 1989) and their concentrations vary with the seasons, from year to year and with the physiological age of the plants. Toxicity peaks during flowering and seed production. Although Groundsel is not preferred forage, livestock may inadvertently eat it along with other stored forage during winter and in the spring. The leaves and the flowerheads are both toxic and, as with S. jacobaea, the poisonous alkaloids are not destroyed during plant drying during hay production, or when silage is fermented (Mitich 1995).

Herbicide resistance

Forms of S. vulgaris resistant to the triazine herbicides, ie Atrazine and Simazine, first appeared in 1970 in Washington (Ryan 1970). They signalled the beginning of a serious general problem of the selection of resistant weed populations which continues worldwide (Shaner 1995). The primary reason for the selection of herbicide-resistant weed biotypes is the farming practices that have developed since the discovery of selective herbicides, including the spreading of slurry in dairy producing areas and the shift away from multi-crop rotation towards mono-cropping in arable regions (Shaner 1995).

Reduced reliance on herbicides as the primary means of weed control and a concerted move to integrated weed management programs involving tillage, mowing, crop rotation, machine- and seed-hygiene, and the use of new and 'traditional' herbicides of diverse modes of action will all b e required to contain the problem. Groundsel has shallow fibrous roots and is easily uprooted by hoeing, although it very rapidly reappears in any recently disturbed topsoil.

Farmers must be able to adopt these programs while maintaining financial viability. Effective herbicide resistance management needs to involve government agencies and research in both academic and industrial sectors in order to incorporate new and established herbicides with existing cultural, mechanical and biological control methods.

British and Irish occurrence

The BSBI Atlas 2020 hectad map shows S. vulgaris is almost ubiquitous throughout B & I at this level of discrimination, occurring from sea level to 469 m in Lanarkshire, Scotland (VC 77). There has been no significant change in the overall hectad distribution of the species since the 1960s, although a decline on higher ground in parts of Scotland is attributed to a reduction in active farming of marginal land (H.K. Killick, in: Stroh et al. 2023). The advent of herbicide resistant forms of the species has probably led to an increased presence in arable fields and their margins, as well as in gardens and other urban areas.

European and world occurrence

A member of the European southern-temperate phytogeographical element, S. vulgaris is considered native across all of W Europe but it has been subsequently spread with agriculture and is now common throughout Europe, stretching northwards to 71oN (Sell & Murrell 2006). It may also be native in W Asia, W Siberia and SE China, but has spread right across to Japan. S. vulgaris has been recorded throughout the Mediterranean except Crete and in Morocco, and may just possibly be native there, but it does not appear to occur elsewhere in N Africa. Beyond the mentioned areas, S. vulgaris has spread widely with agriculture and transport of goods to most of N and parts of S America, and in the southern hemisphere to the Falkland Isles, Cape Province in S Africa, S, W & SE Australia and Tasmania and New Zealand, becoming Circum-polar southern-temperate (Hultén & Fries 1986, Map 1848; Webb et al. 1988). In all its introduced territory in Canada, it has become naturalised (Robinson et al. 2003) and the same is true in New Zealand (Webb et al. 1988).

Medicinal uses

Groundsel was used in herbal medicine for poultices to draw out pus and for easing pain caused by wounds or even for treating toothache. It was also considered a simple and easy to use purgative and a stronger infusion, mixed with ale, provided a gentle emetic that caused no irritation or pain and greatly eased stomach cramps. Applied externally as a lotion it was used for cooling inflammation including bruises, swellings and chapped skin (Grieve 1931; Allen & Hatfield 2004). On account of its toxicity, it no longer appears in the British Pharmacopoeia.

Names

The genus name 'Senecio' is a name from Pliny derived from the Latin 'senex' meaning 'old man', a reference to the white plumed pappus head of the fruiting inflorescence (Gilbert-Carter 1964). The Latin specific epithet 'vulgaris' means 'common'. Fifteen English common names are listed by Grigson (1955, 1987), the familiar 'Groundsel' being derived from the Old English 'grundewilige', meaning 'ground-swallower', a reference to the ability of the weed to rapidly spread and take over bare ground in the garden or field. Other English names carry the same message, including 'Grinsel', 'Groundswell', 'Grunswell', 'Groundwill', 'Grundy-swallow' and 'Swallow-grund'. S. vulgaris also gets the names 'Birdseed', 'Canary seed', 'Canary food', 'Chickenweed' and 'Chickweed' from the fact that in the past its leaves and seedheads were fed to cagebirds and other fowl in wintertime.

Threats

A very successful ruderal in a wide range of fertile, artificial habitats, despite standard weed control measures it remains very common. While S. vulgaris has declined in arable fields in Denmark (Andreasen et al. 1996), it appears to have increased significantly in England in the period up to 1988 (Rich & Woodruff 1996). Herbicide-resistant Groundsel is part of a worrying problem which requires integrated weed management and less reliance on selective herbicides than was common in the recent past.

References

Grime, J.P., Hodgson, J.G. and Hunt, R. (1988, 2007); Hackney, P.( Ed.) and Beesley, S., Harron, J. and Lambert, D. (1992); Gilbert-Carter 1964; Grigson (1955, 1987); Andreasen et al. 1996; Rich & Woodruff 1996; Grieve 1931; Allen & Hatfield 2004); Stroh et al. 2023; Hultén & Fries 1986, Map 1848; Webb et al. 1988; Sell & Murrell 2006; Ryan 1970; Shaner 1995; Mitich 1995; Brown & Molyneux 1996; Hallett et al. 1990; Paul & Ayres 1987; Ridley 1930; Bergelson et al. 1993; Kempen & Graf 1981; Harper and Ogden (1970); Salisbury 1942; Briggs & Block 1992; Trow 1912; Warren (1988); Stace 1991; Meikle et al. 1975; Kadereit 1984; Robinson et al. 2003; Melderis & Bangerter 1955; Thompson et al. 1997; Briggs et al (1992); Lawson et al (1992); Hartmann et al (1989).