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Tanacetum vulgare L., Tansy

Account Summary

Introduction, garden escape, very rare. Euroasian boreo-temperate, but very widely naturalised including S Australia and New Zealand.

1884; Barrington, R.M.; from Lady Brooke Bridge to northern Geaglum Quay.

April to September.

Growth form, Irish status and preferred habitats

This tall, attractive, fern-leaved, aromatic perennial with a creeping rootstock and wiry roots is recognised in NI as a rare garden escape or relict of cultivation, chiefly associated with old house-steads. In Ireland overall, it is considered an occasional alien species of roadsides, ditches and waste places, usually occurring near houses (An Irish Flora 1996). The plant produces one or more erect, angular, furrowed, purplish stems, 30-150 cm tall, that branch in their upper part to form a ± flat-topped corymb inflorescence. The stem-leaves are deeply and beautifully pinnately divided, the almost linear lobes with deeply and acutely toothed segments (Butcher 1961).

Fermanagh occurrence

Hackney et al. in the FNEI 3 considered it, "probably not long-persistent at most sites", in the three VCs covered by that work, yet RHN and the current author (RSF) believe Tansy is reasonably persistent and well naturalised in its few Fermanagh sites. Judging from the state of the old walls and ruined house-steads by which it shelters, eg at the Monawilkin and Marlbank sites, it must have survived here untended for at least 50 or 60 years. It is true, however, that while there are Fermanagh records from a total of eleven widely scattered tetrads, the plant has only been recorded from four of them in the post-1975 period. T. vulgare is much less frequent in Fermanagh than T. parthenium (Feverfew) and although gardens are very much subject to fluctuations in fashion, it is probably also much rarer in cultivation at present than previously was the case.

Flowering reproduction

T. vulgare flowers from July to September, the flat-topped, branched inflorescence forming a dense, compound corymb composed of many flowerheads each 7-12 mm in diameter. The number of flowerheads per inflorescence can varying enormously, and while usually this falls within the range 10-70, it can be as few as five or as many as 100 per plant (Sell & Murrell 2006). Considering the number of scented, yellow, bisexual tubular-florets, 3.5 mm long, that each button-like flowerhead contains must be 50 or more, this means an individual insect visitor can walk about on top of many hundreds of tubular florets crowded together, very rapidly pollinating many of them (Hutchinson 1972).

The flowers attract a wide range of small insects as pollinators, and the achenes produced after fertilisation are c 1.5 mm long, cylindrical, 5-ribbed, yellow and topped by a distinct collar that represents a reduced pappus (Butcher 1961; Clapham et al. 1987; Sell & Murrell 2006).

British occurrence and preferred habitats

The BSBI Atlas 2020 hectad map shows T. vulgare is very widely distributed throughout lowland Britain, becoming somewhat less frequent in N Scotland. While it is widely distributed, it is no longer common, no doubt the noticed decline in the wild, reflects its current unfashionability in modern gardens.

It characteristically occurs on a wide range of soils, preferring moist to damp, winter-wet, moderately nutrient-rich, base-rich substrates and avoiding chalk, clay and the most acidic situations. It typically grows in grassy places along linear habitats including roadsides, railways, hedgerows and the margins of rivers, plus in open, waste-ground sites. The rough or semi-managed grasslands it occupies are seldom grazed, but they may be occasionally mown (Sinker et al. 1985; Crawley 2005; H.J. Killick, in: Stroh et al. 2023).

Tansy can become abundant on suitably fertile grassy habitats, but while it is regularly capable of long-persistence, it has little ability to spread, its seedlings being totally unable to establish in closed sward vegetation and requiring open, bare patches, conditions usually created by some form of occasional disturbance, including for instance flooding, trampling or vehicle parking (Crawley 2005).

In ecological terms, the established strategy of T. vulgare is categorised as C/SR meaning it is intermediate between a straight Competitor and a Stress-tolerant Ruderal species (Grime et al. 1988, 2007).

The major published soil seed bank survey of NW Europe uncovered seven estimates of buried seed survival for T. vulgare, five of which reckoned it was transient (ie survived less than one year). Of the remaining two estimates, one of them considered that seed was short-term persistent (ie survived more than one year but less than five), and the last study recognised seed was present in the soil, but could not decide which of the other three survival categories it fitted into (Thompson et al. 1997).

Fossil record and status in Britain

The status of the species in Britain is probably more, 'assumed native' than anything else, since the plant has been in cultivation for hundreds of years and frequently escapes into the wild. The only fossil record of Tansy noted by Godwin (1975) is in the Middle Pleistocene Cromer Forest Beds, which represent the Cromerian Interglacial and preceding stages. No fossil evidence at all exists in Britain from the current Flandrian post-glacial stage.

In a major revision of the status of numerous British species previously assumed native, Preston et al. (2004) listed T. vulgare (their Table 8), as a species they considered native or doubtfully native species in Britain on ecological grounds, that has been categorised as an archaeophyte, or probable archaeophyte, in one or more of four European countries that they examined. In the case of T. vulgare, it has been listed as an archaeophyte in the Czech Republic and as a doubtfully (or possibly) archaeophyte species in Germany.

In British Floras, the status of T. vulgare has fluctuated somewhat in the last 35 years, since while Clapham et al. (1987) and Stace (1997) described Tansy as native, Stace (2010) listed it as an archaeophyte and Stace (2019) considers it, "possibly native". Due to the equivocal nature of the evidence involved, it is not yet possible to be certain on which side of the line, native or alien archaeophyte, the status of T. vulgare will eventually fall (Stace & Crawley 2015).

European and world occurrence

T. vulgare belongs to the Eurasian boreo-temperate phytogeographical element and while widespread throughout Europe, it is considered native in parts of S & E Europe including the Caucasus, Armenia and Siberia (Sell & Murrell 2006). It is rare or absent in most of the Mediterranean region and from N Africa. Tansy has been widely spread by former garden cultivation for medicinal and ornamental purposes and has been introduced into N & S America, S. Australia and New Zealand. In E Asia, it is replaced by a taxon described as T. boreale Fisch. Ex DC., or as var. boreale (Fisch ex DC.) Trautv. & Mey (Hultén & Fries 1986, Map 1810).

Uses

The entire Tansy plant is bitter, acrid and aromatic and it has a long history of cultivation as a valued medicinal and domestic repellent herb (Grigson 1955, 1987). However, an Irish text recommends, "The curled variety common in gardens is considered the mildest and most wholesome for use." (Mackay 1836). Despite its bitter flavour, cattle and sheep are said to graze the plant, but horses, goats and pigs avoid it (Grieve 1931).

The principal medicinal uses of the herb are as a vermicide (ie to kill internal worms) and it was mainly used on children. It was also used externally as a vulnerary (ie for healing wounds and bruises) (Grieve 1931). Human poisoning has occurred by medicinal use of the aromatic oil or infusions of the leaves, so Tansy is no longer recommended (Cooper & Johnson 1998

Tansy is not safe as an edible pot-herb either, since in larger doses it is a violent irritant, but it has long been valued as a repellent, being laid on top of stored corn seed to keep away mice, or rubbed on meat to keep off flies (Grigson 1955, 1987).

Threats

None.

References

Hackney, P.( Ed.) and Beesley, S., Harron, J. and Lambert, D. (1992); Webb,D.A., Parnell,J. and Doogue,D. (1996); Godwin, H. (1975); Grieve, M. (1931); Grigson, G. (1955, 1987); Stace, C. (1997, 2010, 2019); Clapham, A.R., Tutin, T.G. and Warburg, E.F. (1987); Mackay, J.T. (1836); Stace & Crawley 2015; Sinker et al. 1985; Crawley 2005; Butcher 1961; Cooper & Johnson 1998; Sell & Murrell 2006; Hultén & Fries 1986; Grime et al. 1988, 2007; Hutchinson 1972; Stroh et al. 2023; Thompson et al. 1997); Preston et al. 2004.