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Rumex conglomeratus Murray, Clustered Dock

Account Summary

Native, locally frequent to common, widespread. Eurosiberian southern-temperate, but widely naturalised in both hemispheres and now circumpolar.

1881; Stewart, S.A.; Co Fermanagh.

May to November.

Growth form and preferred habitats

Docks in general are a difficult group to identify accurately, really requiring well-grown plants with ripe fruits to be certain of naming them correctly. To make matters worse, P.D. Sell carried out a detailed study around Cambridge and found that early flowering stems often did not produce viable fruit and seeds, even when the plant otherwise appeared a good specimen of the species. The same ticket-marked plant would then form ripe fruit and viable seed on fresh stems later in the year. Thus the same plant, whether species or hybrid, could be sterile or fertile at different times of year according to circumstances (Sell & Murrell 2018).

R. conglomeratus is a very variable, short-lived, tap-rooted perennial that typically flowers from July to October. Along the several inflorescence branches, leafy bracts occur on the basal two-thirds to three-quarters or even more of their length in this species. In comparison, R. sanguineus (Wood Dock) has its inflorescence bracts confined to the basal one-third to one-half of each flowering branch (Stace et al. 2015). The greater extent of bracts in the lower part of the Clustered Dock inflorescence, its more open, wider-spreading flowering branches, and the fruiting sepals (or tepals) with three pronounced swollen, oblong, corky tubercles per flower surrounding the solitary nut or achene, together help to distinguish R. conglomeratus from the rather similar R. sanguineus, which in Fermanagh is the more widespread species of the two (Lousley & Kent 1981; Garrard & Streeter 1983).

Essentially, R. conglomeratus is a pioneer colonist, most frequently associated with muddy, somewhat disturbed, open, unshaded, low-lying ground around eutrophic lakeshores, stream-sides and bare soil or patchy vegetation near ditches, paths and gateways. Typically, these areas are subject to flooding in winter, or occasionally they temporarily flood after heavy or prolonged rainfall at other times of year. The occurrence of the species is associated with the high water mark at which floating achenes (nutlets) become stranded amongst other drift materials and where, after winter exposure, they may germinate in the spring and establish (Vergnano 1966; Lousley & Kent 1981; Roberts & Boddrell 1985).

R. conglomeratus is also very frequently associated with wet, muddy, artificial, man-made habitats, or those heavily influenced by man and/or his stock animals (ie like R. crispus (Curled Dock), it is a definite apophyte). Sometimes it also behaves as a ruderal on wet or waterlogged waste ground, eg in abandoned quarries, waste tips and gardens. It also more rarely appears on damp to wet, grassy roadside verges.

Buried achenes of R. conglomeratus can survive burial in soil for more than one year but less than five (Thompson et al. 1997). In comparison, R. sanguineus displays a rather wider range of ecological tolerances than R. conglomeratus, including growing in shade and in quite a lot drier ground, eg on wood margins, waysides and in other ruderal situations.

Apart from its special soil-water relations, Clustered Dock requires or is confined to open, ± unshaded, moderately fertile, mildly acid to calcareous situations. Its presence in meadows, pastures and roadside verges speaks of its tolerance of occasional mowing and/or some degree of grazing pressure, but it is definitely commonest in the more open, pioneer communities of intermittently disturbed habitats where aggressive competition from vigorous accompanying species is absent or severely limited.

Fermanagh occurrence

Locally, R. conglomeratus has been recorded in 128 tetrads (24.2%), while the comparable figure for R. sanguineus is 204 tetrads (38.6%). Clustered Dock, nevertheless, is a locally frequent or even common plant in Fermanagh, being quite typical of rather wet, marshy, lowland habitats, especially around the margins of lakes and ponds. It is frequent about both parts of Lough Erne and along the banks of the River Finn and its lakelets. However, as the tetrad distribution map indicates, it is only thinly scattered elsewhere in the VC.

Hybrids

Hybrids are formed with eight other Docks which share wet ground with R. conglomeratus, including several that are common or locally abundant species in our area, R. sanguineus (Wood Dock), R. hydrolapathum (Water Dock), R. crispus (Curled Dock) and R. obtusifolius (Broad-leaved Dock) (Lousley & Kent 1981). However, none of these Dock hybrids have yet been identified in Fermanagh. The hybrid with R. sanguineus (Rumex × ruhmeri Hausskn.) is the most likely one to occur but it is difficult to recognise since the parent species and their variability are very similar (Stace et al. 2015).

Hybrids are said to resemble either parent, or they may be intermediate between the two in many characters. The hybrid is also fertile which compounds the identification problem (Sell & Murrell 2018). The number of fruiting tubercles can be one, two or three but it is most often three (which is the usual number in R. conglomeratus), although in the hybrid one of the three is larger. The tubercle shape in the hybrid is typically elongate (not ± spherical as is usual in the single tubercle of R. sanguineus) (Stace et al. 2015).

Since the pattern of variation shown by the hybrid tends to overlap that of each parent, its identification is only convincing when it shows not only reduced fertility but also a mosaic of parental characters or several intermediate characters. In Stace et al. (2015), there are a total of just 15 widely scattered hectads across Ireland with records of this particular hybrid.

Toxins

Like other Docks, R. conglomeratus contains oxalates and other toxins, which might deter some if not all kinds of herbivores.

Irish occurrence

The New Atlas shows R. conglomeratus is quite frequent and widespread in Ireland, if somewhat patchy in its occurrence. However, there are areas of the N & W (ie Donegal (VCs H34, H35) & Connemara (H16)), where it is absent or unrecorded. This might be partly explained by the prevalence of strongly acid, nutrient-impoverished soils in these areas, together with a high proportion of upland terrain which would also be unsuitable for this species.

British occurrence

The New Atlas map shows that in Britain Clustered Dock is widespread in lowland England and Wales and rare or absent in mountain areas. It becomes increasingly scarce and more obviously apophytic as one moves north into Scotland (Preston et al. 2002). In NE Scotland (eg near Inverness), the native status of the species was regarded as 'doubtful' by Mary McCallum Webster (1978), and she rejected as errors many older records in the N & NE of the country.

European and world occurrence

R. conglomeratus is widespread throughout W, C and S Europe and N Africa, in the north reaching Denmark and the southern tip of Sweden, but only an ephemeral alien elsewhere in Scandinavia (Jalas & Suominen 1979, Map 460; Jonsell et al. 2000). It has been spread, presumably by agriculture, widely beyond its native range into the Azores, S Africa, N Turkey, the Caucasus, N Iran, C and E Asia, N and S America, S Australia and New Zealand (Hulten & Fries 1986, Map 668).

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 'conglomeratus' means 'crowded together' and refers to the clustered flowers and possibly the three tubercules on the inner tepals surrounding the nut or achene fruit (Gilbert-Carter 1964). The English common name 'Clustered Dock' is a mere modern book name of no folklore significance being a straightforward translation of the specific scientific name.

Threats

None.