Thalictrum minus L., Lesser Meadow-rue

Account Summary

Growth form and habitat preferences

T. minus is a extremely variable, clump-forming stoloniferous perennial species or species aggregate, the differing growth forms being produced by the orientation and length of its rhizome, which can be either ascending and short, or horizontal and long (Clapham et al. 1987). The plant produces erect stems, variable in form and colour and up to 120 cm tall, but in Fermanagh often much less, most typically around 50-60 cm in height. Variation in the species also extends to the wide variety of habitats it occupies. Again, in a local context, these range from fairly dry to quite moist, lime- or base-rich conditions. The three or four times pinnately divided leaves are also very variable, but the ultimate leaflets are generally about as long as broad, a fact which clearly distinguishes the species from T. flavum, which is much less finely divided and generally grows under quite different ecological conditions. In comparison, T. flavum is a plant of very much wetter and more open sun-lit, marshy grasslands and fen-like habitats.

In Great Britain, T. minus is also represented in at least three rather different types of habitat that are identified by Clapham et al. (1962), as: i. limestone rocks and grassland; ii. coastal dunes; and iii. streamside or lakeshore gravel and shingle. To the first of these we should also add cliff ledges, screes and the gryke (or grike) crevices of limestone pavement (Halliday 1997).

Fermanagh occurrence

In Fermanagh, T. minus has been recorded in a total of eleven tetrads (2.1%), eight of which have post-1975 records. It is chiefly distributed around Lough Erne and Lough Melvin and along stretches of the Colebrooke River. In Fermanagh, T. minus typically occurs as very small populations of just a handful of scattered individuals, or as isolated clumps growing in fairly dry, rocky or sandy lakeshore situations, or in similar soils on river banks under the shelter and shade of scrub. Unless active conservation measures are taken to reverse the present decline, these small, fragmented populations represent the end of the line for T. minus in Fermanagh. Small, isolated populations inevitably suffer from poor cross-pollination, consequent inbreeding depression and a loss of fertility. Undoubtedly all such rare and scattered species populations are on the downhill slope towards local extinction at some future date. In the case of T. minus, the existence of some degree of apomixis may delay matters for a while, but eventually fragmented species like it are fated to fade out and disappear.

Variation

The New Flora of the British Isles (Stace 1997) accurately describes the species or species aggregate as, "very variable and little understood". Stace also points out that while up to eight subspecies or other rank of taxa have been described on the basis of fruit, habit and hairs, the variation has not been properly studied. Until it is, his opinion chimes with my own, "these variants are not worth recognising". Matters are complicated by the fact that some races within the species or species aggregate appear to be apomictic and can thus set asexual seed, which is a rather sophisticated form of vegetative reproduction.

By whatever means the plant manages to reproduce, once it becomes established in a site T. minus becomes very persistent. It still survives, for instance, on the banks of the Colebrooke River where Smith found it and at Gubbaroe Point in crevices in the limestone pavement shore of Lower Lough Erne, two sites where it was originally found in the second half of the 19th century.

Irish occurrence

T. minus used to have other inland stations in Northern Ireland, but with the exception of the Fermanagh records and a few stations in the Mourne Mountains, Co Down (H38), practically all the remaining Northern Irish stations for the species are on coastal sand dunes, where they are sometimes distinguished as subsp. arenarium (Clapham et al. 1987; FNEI 3).

In the Republic of Ireland, T. minus is confined either to the coast or to the shores of larger lakes in the west and in the Central Plain, with a few additional stations, mainly in the mountains of Cos Sligo (H28), Leitrim (H29) and the Connemara region in the mid-west of the country. In these mountain stations, Lesser Meadow-rue occupies rocky ground and mountain ledges where it can avoid intensive plant competition; at the same time it is less accessible to browsing sheep (Walters & Perring 1962; Preston et al. 2002).

Toxicity and medicinal uses

Browsing this herb must be a mixed pleasure for stock animals, since like other members of the Ranunculaceae T. minus contains the bitter tasting and highly irritant toxin, protoanemonin (Cooper & Johnson 1998). In common with T. flavum, T. minus is the subject of a great deal of current pharmaceutical research since both species contain several additional poisonous alkaloids, including berberine, although thalactamine is the main ingredient in the toxin cocktail in T. minus. Berberine is used in modern medicine to treat stomach and gall bladder ailments (Urmantseva et al. 2000).

Garden cultivation and occurrence in Great Britain

T. minus has also had a long career in Britain and Ireland as a garden border perennial. It is certainly not grown for its flowers, but rather for its attractive finely dissected foliage which is greatly appreciated by florists and flower arrangers (Robinson 1909, p. 888). Due to these widespread garden populations, T. minus also regularly jumps the garden wall and occurs as an established introduction. In Great Britain, these garden escapes sometimes become intermixed with supposed native plants, mainly in the Midlands, S & SE England and in Wales, although it can perhaps more rarely occur in this way as far north as Glasgow (Preston et al. 2002).

European occurrence

T. minus is widely but unevenly spread throughout continental Europe, being rather less frequent on the Atlantic coastline than the extent of the species or aggregate distribution in the British Isles would suggest. It occurs up to 70N in Scandinavia but is absent from much of the rest of Norway, Sweden and Finland, and, indeed, it appears to have declined in the latter two countries. On the Iberian Peninsula, T. minus penetrates to the southern Spanish Sierras and it also occurs rarely on Corsica, Sardinia and Sicily, yet is absent from the Peloponnese, Crete and the smaller Mediterranean islands (Jalas & Suominen 1989).

World occurrence

Beyond Europe, the distribution of T. minus stretches to N, E and S Asia, Ethiopia, S Africa and Alaska (Jonsell et al. 2001).

Names

The Latin specific epithet 'minus' is a comparative of 'parvus', and means 'smaller than', presumably smaller than T. flavum, which generally is the case (Gilbert-Carter 1964). The plant appears to have been insufficiently known or was ignored as being of little or no interest or use, so it does not appear to have accumulated much in the way of English common or local names, apart from 'Lesser Meadow-rue' (see T. flavum species account). Gerard (1633, pp. 1251-2), however, distinguishes it from T. flavum as, 'Small Bastard Rhubarb', and for an explanation please again see the T. flavum account.

Threats

The Colebrooke River sites could easily be destroyed by river bank improvements and the Muckross site by tourist developments.

• Find out more about the format of the species accounts
• View abbreviations
• View references for all species accounts
• View a gazetteer of all the sites