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Eupatorium cannabinum L., Hemp-agrimony

Account Summary

Native, occasional. European temperate, but sparsely introduced into N America and Queensland, Australia.

1884; Barrington, R.M.; Blaney Bay, Lower Lough Erne.

April to November.

Growth form and preferred habitats

An erect, stout, leafy perennial, with simple stems or shortly branched above, up to 175 cm tall. The opposite, palmately-lobed, 12 cm leaves are cut almost to the base and they are coarsely, serrate toothed on their margins. The showy clustered flowerheads, produced late in the season, are entirely composed of pinkish-purple, tubular florets, borne in terminal corymbs. The numerous opposite, broadly ovate, three- or five-lobed leaves of the plant resemble to some extent those of Cannabis sativa (Hemp) and hence the Latin specific epithet and first part of the English common name. Upper stem leaves are simple, lanceolate or ovate, acuminate, margins toothed, wedge-shaped at the base and stalkless (Sell & Murrell 2006).

As one would expect with such a tall perennial, liberally branched at the top, the root-stock and base of the plant are decidedly woody to provide the essential mechanical physical support to withstand buffeting by wind. The stem is reddish in colour, downy hairy above and smells pleasantly aromatic when cut. The stem leaves are on short stalks and are sparsely furnished with small resinous glands. The leaves give off a pungent smell when bruised, which strangely is more reminiscent of an umbellifer (Apiaceae) than of other composites (Asteraceae) (Grieve 1931).

E. cannabinum often behaves as a semi-aquatic species, usually in clumps, growing on a wide range of constantly damp or wet, lowland base-rich soils, often in situations with a variable water-table, marginal to water bodies. These habitats typically include the banks of ditches, streams, rivers, ponds and lakes, involving vegetation such as grassy marshes, tall-herb fens, swampy ground in fen marshes, bogs and the margins of wet woods. It can also occur in clearings and rides in damp woods, including conifer plantations, and at coasts in flushed areas of cliffs and in sand dune slacks (Garrard & Streeter 1983; M.J. Wigginton and K.J. Walker, in: Stroh et al. 2023).

Hemp-agrimony is also capable of growing more infrequently on drier soil conditions, such as calcareous grassland with outcropping limestone and on more or less damp roadside banks, on moors, on the margins of dry woods, on railway embankments and in rough grass waysides (Hutchinson 1945, 1972; Reynolds & Reynolds 2013). In the Burren, Co Clare (H9), it is frequent in the deep, open crevices (grikes) in karst limestone pavement (Webb & Scannell 1983).

The soils it frequents vary from moderately acidic to calcareous, but they are always fertile and, although it most often occurs on base-rich clay, silt and less often sand, it can also frequent stony or rocky, again often calcareous conditions – the latter reflected in one of the alternative common names, 'Gravel root' (Grieve 1931; Sinker et al. 1985; Flora of Lough Neagh; Hill et al. 1999; Green 2008).

Fermanagh occurrence

In Fermanagh, E. cannabinum has been recorded in 41 tetrads, 7.8% of those in the VC. The local habitats include marshy ground on stream-sides, ditches, wet woodland at the base of cliffs and on stony or rocky lakeshores. E. cannabinum is chiefly distributed about Lower Lough Erne, Lough Melvin and Lough Macnean.

It is most frequently found with tall fen species such as Epilobium hirsutum (Great Willowherb), Phragmites australis (Common Reed), Sparganium erectum (Branched Bur-reed) and Typha latifolia (Bulrush), or, when grazed among smaller sedges, plus Angelica sylvestris (Wild Angelica), Filipendula ulmaria (Meadowsweet), Lysimachia vulgaris (Yellow Loosestrife) and Molinia caerulea (Purple Moor-grass) in a so-called 'mixed sedge' community (Prime 1977). The presence of E. cannabinum in this company indicates that the species must be strongly competitive to survive. The established strategy is described as Competitor by Grime et al. (1988, 2007), confirming this appraisal.

Flowering reproduction

Hemp-agrimony flowers from late summer through into autumn (July to September), producing terminal, crowded, ± flat-topped or somewhat domed corymbs of huge numbers of tiny flowerheads, 1-5 mm in diameter, each containing just five or six dull pink-mauve or whitish, tubular, bisexual florets (Butcher 1961; Sell & Murrell 2006) and hence another English common name, local to the Isle of Wight, 'Raspberries-and-cream' (Grigson 1955, 1987). The flowers are visited by bees, butterflies, moths and flies for floral food, but if they are unvisited, flowers within the same flowerhead can automatically cross-pollinate (Clapham et al. 1962).

The achenes are black, 2.5-3.0 mm long, oblong, truncate, or tapering at both ends (ie fusiform), five-angled, four-six ribbed, gland-dotted and they are crowned by a white or dirty white pappus, 4-5 mm long, composed of a single ring of toothed, silky hairs, that acts as a parachute for wind dispersal (Melderis & Bangerter 1955; Butcher 1961; Sell & Murell 2006).

The huge number of flowerheards and florets on a single plant of typical size and fecundity must produce several thousand achenes, but the current author has not managed to uncover any actual measures of reproductive capacity in the literature – a project awaits anyone interested! Freshly collected achenes germinated at a rate of 50% and, after storage for 12 months at 5°C, this figure fell to 38% (Grime et al. 1981).

This statistic suggests seed is not long lived, but examination of the data in the survey of soil seed banks in NW Europe found a total of ten estimates of survival ability: four studies suggested seed was transient (surviving for less than one year); two estimated that it was short-term persistent (survived one to five years); three studies believed it was long-term persistent (surviving at least five years; and one study found seed in soil but could not ascertain its longevity (Thompson et al. 1997). The current author (RSF) reckons these estimates indicate buried seed survival of considerable, but unknown duration.

Fossil history

The fact that E. cannabinum often grows in wet, swampy ground undoubtedly favours the preservation of its fruits as fossils and therefore provides a substantial record of its interglacial history in B & I. Oddly, however, although there are fossils from the ancient Cromer Forest Bed series, and it is represented in the first three stages of both the following Hoxnian and Ipswichian interglacials, and from Zones V to VIII of the current Flandrian interglacial, fossils of it did not appear in any part of the Weichselian glacial phase, either early or late stages (Godwin 1975).

British and Irish occurrence

E. cannabinum is widespread and common throughout lowland areas of England and Wales but, overall, it has a predominantly southern distribution in both B & I. In Ireland, it has occurred in every VC (Cen Cat Fl Ir 2), but it is very local in NE Ireland, including around Lough Neagh (FNEI 3). The Atlas 2020 hectad map shows it is more prevalent and better distributed, and perhaps could be described as 'frequent', south of a line on the map between the cities of Galway and Dublin. Elsewhere in Ireland, it is scattered and is often confined to coastal squares (Stroh et al. 2023).

In Britain, the distribution of Hemp-agrimony has not changed greatly since the 1960s, but it still becomes rare and distinctly coastal north of a line drawn between Newcastle-upon-Tyne and Carlisle (BSBI Atlas 1962, 1976; New Atlas 2002; Atlas 2020). In Scotland, E. cannabinum is local and mainly coastal. It was absent from Orkney (VC 111), Shetland (VC 112) and the Outer Hebrides (VC 110) (Garrard & Streeter 1983; Sell & Murrell 2006), but the Altas 2020 survey now displays a solitary hectad record occurring on both Orkney and the Outer Hebrides.

The commentary on the hectad maps in the Atlas 2020 remarks on increases and decreases as 'turnover' of the species in Britain, meaning some losses are considered due to destruction of wetlands in areas where E. cannabinum has always been scarce, but these losses are being compensated for by new records in other areas, due to a combination of better, more intensive recording effort, the fencing off of ditches and other wet ground preventing trampling and grazing and the possibility of additions from garden escapes. However, overall, it is reckoned, on the basis of effort-adjusted hectad data analysis, that losses of E. cannabinum have continued to occur in both B & I, both post-1930 and continuing post-1987 (M.J. Wigginton & K.J. Walker, in: Stroh et al. 2023).

European and world occurrence

A member of the European temperate phytogeographical element, E. cannabinum is widespread in Europe from the Mediterranean northwards to southern Scandinavia. In the latter, it is common only in the south of Sweden and Finland, where even local occurrences barely reach 62oN or 63oN respectively. As Godwin (1975) points out, "This distribution pattern lends apparent significance to the absence of the plant from the Weichselian glacial stage and its late Flandrian extension.".

E. cannabinum extends S & E from Europe to adjacent parts of N Africa and W Asia and it has local outliers further eastwards from Asia Minor to N India and beyond in C Asia.

It has been "sparsely introduced" in both eastern and western N America and in Queensland, Australia (Hultén & Fries 1986, Map 1764). E. cannabinum has also been recorded, "only from waste places in one location (Hawera (Taranaki))" in New Zealand in 1975 (Webb et al. 1988). The New Zealand plant is referable to the type variety, ie it is not an escaped garden form (Webb et al. 1988).

Toxicity

E. cannabinum leaves contain a volatile oil, tannin and a bitter chemical principle, which protect the plant from all types of herbivores except goats (Grieve 1931).

Uses

Although it is little used medicinally now, herbalists still recognise it as having cathartic, diuretic and anti-scorbutic properties and regard it as a good remedy for purifying the blood. Homoeopaths use a tincture or a tea for treating bilious catarrh, influenza or for a feverish chill (Grieve 1931). In The Netherlands, it was used as an alterative (ie as a drug reputed to restore normal health), probably as a diuretic or laxative, and as an antiscorbutic, ie as an agent to prevent or cure scurvy. In Belgium, it was used as a cure for jaundice. In England, it was considered a lower class medicine for treating jaundice and dropsy. A poultice using the leaves was considered helpful in extracting pus from boils. It also has a good reputation as a wound herb (Grieve 1931). Despite such written accounts of the medicinal uses of E. cannabinum, Allen & Hatfield (2004) believed, "an element of doubt attached to the folk credentials of the remedy.". Decorative garden varieties of Hemp-agrimony are frequently met in the wild, for example, cv. 'Plenum' and cv. 'Album', and they are regarded as being imposing-looking and undemanding subjects for gardens on moist to damp, sunny situations on nutrient-rich soils (Hansen & Stahl 1993; Griffiths 1994 ).

Names

The name 'Eupatorium' is the classical name in Pliny for our present day Agrimonia eupatoria (Agrimony) and was called after Eupator, a surname of Mithridates, King of Pontus (Gilbert-Carter 1964). E. cannabinum was known to 16th century botanists as 'cannabina aquatica', the 'Water hemp-like plant', and as 'eupatorium adulterinum', 'False eupatorium', to distinguish it from true Agrimony, Agrimonia eupatoria. Sometime in the 18th century, the two old names became combined as a 'book name', and thus we have 'Hemp Agrimony' (Grigson 1974).

There are ten alternative English common names listed by Grigson (1955, 1987), from localities around B & I, most of which are unexplained. The already mentioned 'Raspberries-and-cream' clearly refers to the colour of the flowers, and 'Water Agrimony' recognises a typical feature of the habitat occupied by the species. Two names mention the mother of Jesus, 'Virgin Mary' (in Cornwall) and 'Mary's Little Bush' in Ireland but, again, there is no obvious explanation linking the name to the plant.

Threats

None.

References

Grigson, G. (1974); Sinker, C.A., Packham, J.R., Trueman, I.C., and Oswald, P.H., Perring, F.H. and Prestwood, W.V. (1985); Hill, M.O., Mountfield, J.O., Roy, D.B. and Bunce, R.G.H. (1999); Scannell, M.J.P. and Synnott,D.M. (1987); Perring, F.H. and Walters, S.M.(eds.) (1962, 1976); Gilbert-Carter, H. (1964); Harron, J. (1986); Hackney, P.( Ed.) and Beesley, S., Harron, J. and Lambert, D. (1992); Grieve, M. (1931); Prime, C.T. (1977); Hansen, R. and Stahl, F. (1993); Grigson, G. (1955, 1987); Thompson et al. 1997; Sell & Murrell 2006; Butcher 1961; Stroh et al. 2023; Preston et al. 2002; Hutchinson 1945, 1972; Grime et al. (1988, 2007); Green 2008; Reynolds & Reynolds 2013; Webb & Scannell 1983; Godwin 1975; Hultén & Fries 1986; Webb et al. 1988; Allen & Hatfield (2004); Griffiths 1994; Garrard & Streeter (1983); Clapham et al (1962); Melderis & Bangerter (1955); Grime et al (1981)