Rumex obtusifolius L., Broad-leaved Dock

Account Summary

Growth form and preferred habitats

A very variable, large-leaved, rosette-forming, indigenous perennial with a stout and often deeply penetrating taproot, capable of producing a flowering stem up to 150 cm tall, R. obtusifolius occurs scattered through lowland grassland, field edges and gateways, lakeshores, streamsides, riverbanks, wood margins, as well as in a range of ruderal, disturbed and waste ground habitats. The absence of the species from upland areas and mountain tops in Britain & Ireland is more associated with soil conditions (ie the avoidance of peat) than climatic factors, such as length of the growing season or winter cold, since it grows inside the Arctic Circle in coastal Norway (Cavers & Harper 1964; Jonsell et al. 2000). R. obtusifolius is a very common, troublesome perennial weed of fields cut for silage, and it is listed as one of the world's worst weeds, being important in no less than 37 countries (Holm et al. 1977).

Despite its great frequency across these islands and Europe, Broad-leaved Dock has a low competitive ability as a seedling and it cannot become established in closed vegetation plant communities. Once it produces its deep, branching taproot, however, it becomes very difficult to eradicate. The large leaves and tall stem give the species a great advantage over shallower-rooted grasses and herbs, particularly in drier soils. Nevertheless, it does not persist in well-managed permanent grassland and it is regarded as somewhat easier to eradicate than the closely related R. crispus (Curled Dock).

Variation

R. obtusifolius is a highly variable species and Stace (1997, 2010) lists three varieties occurring in the British flora based on the shape and dentation of the tepals (var. obtusifolius, var. microcarpus Dierb. (= subsp. sylvestris (Wallr.) Čelak.), and an intermediate between these, var. transiens (Simonk.) Kubát.). Stace states that only the first of these is native. On the other hand, in Scandinavia, Jonsell et al. (2000) raise these three forms to subspecies, and the authors state that, "only one of them (subsp. sylvestris) is probably native in less disturbed habitats". They go on to comment that the distributions of the three forms has become widened by increased trade and travelling, and that "their distinctness is now much obscured by hybridization in secondary habitats".

Sell & Murrell (2018) have gone deeper into the variation of the species in Britain & Ireland and have described three subspecies and no less than five varieties of subsp. obtusifolius. Of all these varied forms, they regard only var. obtusifolius as probably native in Britain & Ireland.

However, neither subspecies nor varieties were described or distinguished in any of the eight editions of Webb's Irish Flora (Webb 1977; Webb et al. 1996; Parnell & Curtis 2012), and to date no species subdivisions have been recorded in Co Fermanagh.

Flowering reproduction

R. obtusifolius plants tend to flower freely from the second year of growth onwards and individuals may continue doing so for several years. Large individuals can have over 1,000 self-fertile flowers per inflorescence and they may flower and fruit twice during a season, in early and again in late summer. The number of seed produced varies per plant from less than 100 to more than 60,000 in a single year (Cavers & Harper 1964). The tendency for plants to die after seeding is not as marked as it is in R. crispus. Achenes (nutlets) are shed continuously from late summer to winter and the seed can germinate in any month of the year.

Seed dispersal

The lightweight fruits are mainly dispersed by wind, but they have also been found in cattle dung which suggests, if not proves, that they have been eaten and can be transported internally (Salisbury 1964). Spines on the perianth segments additionally assist dispersal by attaching the nut-like fruits externally to the coats of animals, including man, purely by chance. Seeds may also cling to mud or become embedded in it and be accidently transported (Cavers & Harper 1964).

Abundant R. obtusifolius populations have been associated with intensive silage production and the application of organic manures (slurry) to grassland. Courtney (1985) found that seed remained viable after storage in cattle slurry for 12 weeks. The application of such slurry may not only act as a means of seed dispersal but, even more significantly, concentrated deposits of slurry may also cause localised destruction of the grass sward, introducing gaps, reducing competition and favouring the colonisation and establishment of seedling Docks in grassland (Humphreys et al. 1997).

Germination and dormancy

Seed is extremely variable (polymorphic) with respect to germination and dormancy, but it can persist for 40 years or more and may form a very large seed bank. Cideciyan & Malloch (1982) found that the germination rate of seeds of R. obtusifolius increased as seed size decreased. They also showed that although initial growth was slower from smaller seed, no difference in plant size (biomass) was detectable at the end of the growing season.

Vegetative reproduction

Fragments of underground stem and root can reproduce the species after ploughing. Pino et al. (1995) found that R. obtusifolius had a 'phalanx' type of invasive clonal vegetative growth in grassland, the main structure involved being the stem. Regeneration can occur at depths up to 15 cm, but growth and recruitment is prevented in wet soils (ie those maintained at water-logging or field capacity). This is very significant in a Fermanagh context, since local soils are often this wet. Despite the possibility of vegetative spread, the major means of R. obtusifolius reproduction and dispersal is undoubtedly by seed.

Toxicity

Like other Docks, R. obtusifolius contains oxalates and other toxins which are sometimes said to give it a pleasantly sharp taste, a fact which apparently allows it to remain palatable to some forms of stock (Cooper & Johnson 1998). Mabey (1972) reported that R. obtusifolius (like R. crispus) has been used as 'wild food' in human communities, the leaves being collected very young, cooked and eaten with bacon or ham and a little vinegar. The leaves of both species are bitter tasting, R. obtusifolius being the worst of the two in this respect. In 1990, a Spanish family suffered acute oxalate poisoning after such culinary use of R. crispus, resulting in one fatality (Reig et al. 1990), so its use in the human diet is very definitely not recommended.

Other agricultural research on fodder plants suggests that R. obtusifolius is quite nutritious, being high in protein, low in crude fibre and rich in Mg (Fairbairn & Thomas 1959; Wilman & Riley 1993), and it can be acceptable to dairy cows (Courtney & Johnston 1978). As with other species of Rumex, the conditions under which oxalate poisoning occurs are not clearly defined (Cooper & Johnson 1998). It is generally refused by cattle, sheep and by even more so by choosey animals such as horses. Derrick et al. (1993) found that while the voluntary intake of dried Dock by sheep was satisfactory in their experiments, fresh Dock, especially if chopped, was avoided. The off-putting factor was presumed to be either the taste or the smell of the fresh Dock, which appears to provide the plant with an effective defence against at least some herbivores.

Fermanagh occurrence

R. obtusifolius is the second most widespread and abundant Dock species in Fermanagh, occurring in 459 tetrads, 86.9% of those in the VC. The most abundant Dock in Fermanagh is R. acetosa (Common Sorrel).

R. obtusifolius is widespread and very common throughout Fermanagh, except on the highest, wettest and most acidic ground.

British and Irish occurrence

The New Atlas map shows R. obtusifolius recorded in 95.5% of hectads across Britain & Ireland. It is present everywhere except on the highest ground and in the wettest, most acid peatlands of Scotland and Ireland (Preston et al. 2002).

European and world occurrence

R. obtusifolius occurs in 90% of European territory and has been accidently introduced to every continent (Grime et al. 1988). The European distribution mapped by Jalas & Suominen (1979, Map 465) shows R. obtusifolius widespread in W & C Europe and on the W coast stretching from S Spain to beyond the Arctic Circle in Norway. The distribution thins gradually southwards and eastwards, becoming increasingly scattered in the Iberian, Italian and Balkan peninsulas. Although plotted as native and indigenous throughout most of W, S & C Europe, the accompanying text makes it clear that the species is not native in some areas including Finland, the Azores, "and perhaps elsewhere". R. obtusifolius is shown as introduced on the Macaronesian islands (Madeira, the Canaries and Azores), and to the north in Finland, and up the Baltic coastline of Sweden (Jalas & Suominen 1979, Map 465).

Beyond Europe, R. obtusifolius is very widely introduced in N America and is especially frequent in eastern states of US and Canada. It is also reported from S America, Cuba, S Africa, Japan, Australia, Tasmania, New Zealand and many remote island groups including the Falklands Isles (Hultén & Fries 1986, Map 670).

Possible biological control mechanisms

Studies of grazing by the chrysomelid beetle, Gastrophysa viridula De Geer on Broad-leaved Dock, showed that it resulted in a reduction in both seed number and seed weight (Bentley et al. 1980). In combination with similar debilitating effects on infection by the rust fungus, Uromyces rumicis (Schubiger et al. 1986), there may just be the possibility of a biological control mechanism being developed sometime for this troublesome and very common weed (Hatcher et al. 1994).

Uses

R. obtusifolius is sufficiently common for the astringent properties of the leaf to be frequently used by both children and adults to ease the pain of a nettle sting (see the Urtica dioica (Stinging Nettle) species account on this website). Thus, together with the other common 'Dock' or 'Docken' species, R. crispus (Curled Dock), from which R. obtusifolius is very often undistinguished, the latter has earned its reputation as a generally useful medicinal herb. In this way it has accumulated a good supply of folk names (see below). Although the leaf alone is often applied to a nettle or an insect sting, traditionally a far more effective poultice was made from the roots, by cleaning, peeling and crushing them to a pulp to make a paste (Darwin 1996).

Apart from stings, Dock is used in herbal medicine to treat the pain of burns and scalds, to relieve rashes and to staunch bleeding from a cut (regarded as the second best herb to Plantain (Plantago major or P. lanceolata), which is greatly and universally preferred for that purpose) (Allen & Hatfield 2004). Other medicinal uses are to relieve pain, include leaves for headaches and rheumatism. Boiled seeds have also been used to draw the pus from a wound, to cure boils, to treat all kinds of cough, and for colds and bronchitis. A liquid or tea processed from Dock roots has been considered a curative tonic for cleansing the blood, for keeping scurvy at bay and for liver trouble, including jaundice. The leaves have been used to remove warts and corns (Grieve 1931; Allen & Hatfield 2004).

Names

The genus name 'Rumex' is an old Latin name for Sorrel from Pliny derived from the Latin 'rumo' to suck, from the Roman habit of sucking Sorrel leaves to allay thirst (Johnson & Smith 1946). The Latin specific epithet 'obtusifolius' translates as 'blunt-leafed' (Stearn 1992).

The English common name 'Broad-leaved Dock' is a modern book name based on the Latin scientific specific epithet and as such has no folklore connections. A total of 16 interesting alternative English common names from around Britain & Ireland are listed by Grigson (1987). Apart from 'Dock' and 'Docken' mentioned above, the names 'Butter Dock', 'Butter Docken' and 'Smari Dock' (a Scottish name) refer to the previous convenient practice, in the absence of waxed paper, of wrapping lumps of butter in the large, broad leaf of the plant.

Threats

None.

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