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Thalictrum flavum L., Common Meadow-rue

Account Summary

Native, very rare. European boreo-temperate.

1884; Barrington, R.M.; Killygowan Island, Upper Lough Erne.

June to August.

Growth form and preferred habitats

T. flavum is a rhizomatous perennial of low lying, moist to wet, near-neutral, moderately fertile meso- to eutrophic, base-rich, generally calcareous grasslands. In Fermanagh, some of these particular grasslands were previously used as hay-meadows although they really are rather damp for this purpose. However, the species is also capable of colonising fen sedge peat soils, ie peat formed from the partial decomposition of sedge and herb litter. This type of organic soil has a significantly higher nutrient and mineral content than the much more acid moss peat found in bogland.

The plant possesses a long, creeping, branching yellowish rhizome from which stout, annual, unbranched, furrowed stems arise, and clonal patches can develop if good growing conditions are met (Melderis & Bangerter 1955; Clapham et al. 1962; Hill et al. 1999). Common Meadow-rue generally grows in full sun, but occasionally it is found in light shade.

The erect habit and the fact that its ultimate leaflets are much longer than wide readily distinguish T. flavum from T. minus. In Fermanagh, T. flavum is often on the small side of its size range, only around 50-60 cm tall unless it is forced to compete with taller, ranker vegetation, when it can become extremely lax and straggly. The plant can become so enmeshed with the surrounding, competing, grassy herbage, that it becomes difficult to spot, even when one knows it is present.

Flowering and pollination

The cream to yellowish flowers, which are produced between June and August, are largely composed of the slender filaments of the stamens. In Fermanagh, the stamens are sometimes much more sparse than normal, which again makes the plant easily overlooked even when in flower. The bunches of erect yellowish stamens attract small flies and bees (both bumble-bees and honey-bees). They manage to attract insects without the advantages of nectar, perfume or petals to advertise and reward the visitors; they simply collect and feed on the plentiful supply of nutritious pollen (Proctor & Yeo 1973, p. 60; Garrard & Streeter 1983). Some authorities regard the flowers as fragrant, others not, so there might well be a measure of geographical variation in this particular respect. But then every nose is different! (Proctor &Yeo 1973; Jonsell et al. 2001).

In addition to pollination induced by movements of the insect visitors, very probably some degree of wind pollination of the reduced flowers also takes place (Clapham et al. 1962).

Fruit

Each small flower of the more or less dense branched panicle inflorescence contains 3–12 free carpels (some of which are often abortive). The fruit is a small cluster of single-seeded, almost spherical, ribbed achenes (ie single seeded dry fruits) (Butcher 1961; Hutchinson 1972).

Seed survival

There is a solitary estimate of the soil seed bank longevity of the species in the NW Europe survey (Thompson et al. 1997). This suggests the seed is long-persistent (ie buried seed may persist for at least five years).

Conservation field studies

Information is lacking or difficult to locate on such matters as the scale of seed production, population dynamics, the balance of vegetative versus sexual reproduction, or the competitive ability of the species, studies of which would assist any serious attempts to conserve this declining plant species. The various bodies involved in species conservation in both Ireland and Britain give the impression (deserved or not) that attending meetings, drawing up reports, endlessly revising species lists, drawing boundary lines on maps and arguing for resources are all that they are required to do in order to effectively manage threatened wild populations of plants and animals – work they regard as a business like any other (Marren 2002, p. 307). One wonders when the basic natural history studies, let alone the detailed ecological field studies and localised site observations and analysis that should inform and direct active conservation management are going to be carried out. The conservation industry, if we can call it that, appears much more concerned with words than deeds. Hands and boots need to get dirty to really make a change in species fortunes on the ground.

Fermanagh occurrence

T. flavum occurs very rarely in fens, ditches in wet meadows and in marshy grasslands on lake shores. It has been recorded in a total of just nine Fermanagh tetrads, seven of which have post-1975 records. As the tetrad distribution map indicates, it currently occupies six stations on both shores of the southern half of Upper Lough Erne, but has not been refound at either of the two earliest sites in the VC which lie closer to Enniskillen. In 1996, an interesting new station, quite remote from the seven previous ones, was discovered by a survey team from the EHS on the shore of another of the larger lakes in the county, at the NW end of Lough Melvin. In July 2010, another new site was discovered by RHN and HJN at Derrymacrow Lough, where a solitary plant grew alongside Thelypteris palustris (Marsh Fern).

The other record details are: in damp meadow, W of Lough Digh, 1950, MCM & D; Lough Corby, 3 km W of Newtownbutler, 1983, RHN, also 6 June 2002, RHN, RSF, J.S. Faulkner & I. McNeill, and 11 July 2010, RHN; Drummully Td and Croostan Td shores, 2 km NE of Derrylin, 23 July 1986, P. Corbett & P.J.T. Brain; Derryad Td shore, 13 August 1986, S.A. Wolfe-Murphy & L.W. Austin; S shore of Trasna Island, 19 August 1986, T. Waterman & P.J.T. Brain; SE corner of Corraharra Lough, Mullynacoagh Td, 30 June 1991, RHN, also 15 August 1994, RHN & RSF, 25 July 2004, RHN, and 8 July 2010, RHN & HJN; S shore of Derrymacrow Lough, 11 July 2010, RHN & HJN; shore of Lough Melvin, NW of Garvos, opposite the end of Bilberry Island, 26 June 1996, EHS Habitat Survey Team.

Irish occurrence

The Fermanagh records represent the only nine stations (seven extant) for this rare perennial plant in Northern Ireland outside the Lough Neagh and Lough Beg basin and the connected River Bann drainage system. Even in the latter areas, where once it was frequent, T. flavum is now regarded as being on the decline due to drainage and widespread changes in and intensification of agricultural practices (Harron 1986; Hackney et al. 1992).

In the Republic of Ireland, T. flavum is widely but very thinly scattered, (mainly along the course of the River Shannon) and it is locally frequent in a few central areas of the island (Webb et al. 1996; Preston et al. 2002).

British occurrence

In Britain, the distribution is greatly concentrated to the SE of a line between Swansea and Whitby with a few rare outliers, chiefly coastal, stretching as far north as Edinburgh in the east and Kintyre on the west coast (Preston et al. 2002). With the decline of the species on agricultural land, in many areas of Great Britain, Common Meadow-rue is no longer common. Rather, it has become restricted to relict land, often occurring along linear landscape features such as river banks and roadside ditches (R.A. Fitzgerald, in: Preston et al. 2002).

Significant local factors affecting the widespread decline of Common Meadow-rue in Britain and Ireland include the almost universal move away from hay to silage production, the widespread use of herbicides and the ploughing and reseeding of pastures, very often subsequently fertilised by slurry spraying and/or agrochemical application. These measures have fundamentally altered grassland ecology, increasing production and heightening interspecific competition in ways that force some plants towards local extinction.

Fossil record

The fossil record of T. flavum is almost exclusively based on identification of their characteristic and abundant achenes. Pollen grains can really only be distinguished to the genus level, but the fruits do prove that T. flavum has persisted in the British Isles throughout the last four interglacial periods and the last two glacial periods − at least in the southern part of England and Wales (Godwin 1975).

European occurrence

In Europe, T. flavum is widespread throughout N, W and C regions, stretching N to within the Scandinavian Arctic Circle and S to the toe of Italy and to the Spanish pre-Pyrenees, but the distribution thins markedly further E and it is absent from Greece and all the Mediterranean islands (Jalas & Suominen 1989; Jonsell et al. 2001).

Uses

T. flavum is quite a popular garden border perennial, especially a very fine, large, robust variety called 'Illuminator' (Griffiths 1994). Despite this, there is very little evidence of it as a garden escape in the British Isles, certainly in comparison with several other members of the family (Preston et al. 2002).

The leaves of T. flavum in the past were used to allay fevers, and the root was sometimes used in dyeing (Melderis & Bangerter 1955); supporting evidence for these uses of the plant has not been located. Rather surprisingly, Grieve (1931) makes no mention of the species whatsoever in her very comprehensive herbal.

Toxins

In addition to containing the toxin protoanemonin, common to all members of the Ranunculaceae (Cooper & Johnson 1998), T. flavum contains at least six alkaloids, the principal one being berberine (Velcheva et al. 1992). There is a tremendous amount of current pharmaceutical research going on involving European species of Thalictrum. RSF found that 80 out of 81 scientific papers that were located by a major Internet database searching back as far as 1981 were on this topic alone.

Names and folklore

The genus name 'Thalictrum' is an ancient Classical Greek name first given by Dioscorides to a member of the genus, possibly in the T. minus species aggregate (Gilbert-Carter 1964). The name may be linked to the Greek 'thallo', meaning 'to flourish' or 'to abound in', perhaps a reference to the numerous bundles of stamens in the inflorescence (Johnson & Smith 1946). The Latin specific epithet 'flavum' is straightforward by comparison, translating as 'yellow'.

The plant has four English common names in Britten & Holland (1886), of which 'Meadow-rue' is the most well known, being given on account of the finely divided rue-like leaves. The suggestion made by Gerard (1633, p. 1252) is that some old herbalists confused this species with Ruta graveolens (Rue) which had medicinal uses. Indeed, T. flavum was previously called 'Ruta palustris', or 'Fen Rue', from the appearance of its leaves and its typical place of growth (Prior 1879, p. 77).

The two remaining names in Britten & Holland (1886), refer to T. flavum as 'False Rhubarb' and 'Meadow Rhubarb'. According to Lyte (1578), this was because like Rhubarb the plant has laxative properties and also because it has roots that are yellow like those of Rhubarb! It was also called 'Great Bastard Rhubarb', or 'English Rhubarb' (Gerard 1597, 1633), and it was supposed to cure old ulcers, be good for the belly and act as an astringent 'without biting' (Gerard 1633, p. 1252).

Threats

The Corraharra site could well become overgrown by conifers and the Lough Corby site has already been damaged by drainage.