Ranunculus repens L., Creeping Buttercup

Account Summary

Growth form, ecology and Fermanagh occurrence

This vigorous, rosette-forming, wintergreen, short-lived perennial is very variable in form (especially with respect to leaf shape and degree of hairiness), and it can grow in almost any habitat provided it is damp (except very acidic peat bog), meaning virtually everywhere in Fermanagh! Creeping Buttercup is in fact the second most frequently recorded and widespread plant in the Fermanagh Flora database, being found in 515 tetrads, 97.5% of those in the VC. Creeping Buttercup thrives and, indeed, is most abundant in heavy mineral or clayey soil where drainage is naturally impeded (Harper 1957). In a survey of the Sheffield area, Grime et al. (1988) found R. repens almost entirely absent from infertile acidic soils with a pH below 4.5 and from permanently flooded sites. Creeping Buttercup is also common on wooded, open marsh or fen-fringed lakeshores, riversides and stream banks, on ditches and by roadsides, especially on wet, heavy soils. In these situations, its long creeping stoloniferous stems, rooting at their nodes and their deep, stout, tenacious roots emanating from a short erect rhizome, make the plant extremely difficult to eradicate or control.

R. repens can regenerate from very small root fragments, plus its seeds show dormancy and sustained viability in the soil seed bank (see below for details) and it is also resistant to many herbicides. These factors combine to make it particularly difficult to devise an effective weed control strategy for it in cultivated ground (Lovett-Doust et al. 1990).

In lakeshore grasslands, Creeping Buttercup occupies a zone between drier ground, where it is forced to compete with R. acris (Meadow Buttercup), and wetter soil lower on the shore where Caltha palustris (Marsh-marigold) becomes dominant. R. repens is also a common weed of disturbed soil and gravel and in these more open habitats it can tolerate very much drier conditions, rapidly establishing and spreading vegetatively, its numerous stolons quickly forming large clonal patches (Harper 1957). Salisbury (1964, p. 203) reported that, under favourable soil conditions, an individual plant could spread vegetatively over 4 m² in a single year. However, the species is phenotypically very plastic, and particularly so with respect to stolon production. Stoloniferous growth closely reflects both soil fertility and the intensity of plant competition.

Effect of trampling on populations

Creeping Buttercup can tolerate frequent disturbance and a considerable degree of soil compaction and as a result it is very common around field gates, along paths and on forest and woodland tracks and clearings. Damp, heavy soils frequently become 'poached' or puddled by the hooves of cattle or other stock animals (especially around gates or feeding troughs) and grasses are often killed under these conditions. R. repens is an efficient pioneer species colonising this type of disturbed, bare ground. It invades rapidly through germination of re-exposed buried dormant seed and from nearby plants by the extension of their stolons and the attached rooting plantlets.

The number of daughter plantlets (ie ramets) has been shown to increase with trampling of the vegetation (Diemer & Schmid 2001). The leaves of trampled plants spreading vegetatively in this manner are especially large, which enables R. repens to cover and hold on to previously open patches in the turf or soil and prevent invasion by competing pioneer species (Harper 1957).

Since R. repens possesses an impressive ability to rapidly colonise disturbed ground, to a large extent it has become a follower of man. The plant is a significant weed of gardens, waste disposal areas, building sites, dredgings of river banks, hedgerows, roadsides and, indeed, it occurs on any form of disturbed ground, including in the depressions made by animal hooves which tend to be damper than surrounding ground through holding rain, dew, or water from other sources (Harper 1957).

Turloughs ('vanishing' lakes) − an unusual and specialised habitat

Other open habitats which R. repens occupies in Fermanagh include limestone pavement and scree. In sharp contrast to these latter relatively dry conditions, it also occurs on the shores of a special type of limestone lakes called turloughs (ie so-called 'vanishing lakes' that drain vertically into underground cave systems).

Recent studies in W Ireland have shown that turlough populations of R. repens differ from more typical broad-leaved ruderal plants in both their leaf form (they have more highly-dissected and more glabrous leaves) and in their physiology (the turlough plants have a higher rate of aerial and submerged photosynthesis) (Lynn & Waldren 2001, 2002).

Life expectancy in comparative Buttercup population studies

During detailed population census studies of R. repens and two other buttercup species (see the R. acris species account above), the life expectancy of individuals of R. repens decreased significantly with increasing density of the plant population (Sarukhan 1976). The study also clearly showed that the highest mortality rates per week were obtained, not in the unfavourable phases of the physical environment (ie during the winter), but rather they coincided with active growth phases of the plant (Sarukhan & Harper 1973).

Flowering reproduction

R. repens flowers are quite variable in size and in the number of shiny yellow petals they possess. They contain nectar and are pollinated by honeybees over a 4-9 day lifespan. The curve of the honeybee's body closely mirrors and 'fits' that of the stamen cone of the buttercup to a remarkable degree but while Percival (1955) noted bees actively collecting nectar from R. repens flowers, he remarked that pollen collection has very seldom been seen. Having said this, all buttercup flowers are primitive and unspecialised, meaning that their nectar and pollen flower foods are available to all types of insect visitors. Thus they attract a great many different insect species and are probably pollinated by many of them. The flowers are so unspecialised, they could possibly also be self-pollinated by raindrops (Van den Berg et al. 1985; Proctor et al. 1996; Jonsell et al. 2001). Having said this, cross-pollination is very much the norm, but a low level of selfing is also possible. There is no evidence of apomixis (ie the asexual formation of seed without fertilization taking place) (Coles 1977).

Fruiting performance

Under favourable conditions of slight or negligible competition, the average R. repens plant individual produces five fruit heads although the number ranges from 0-38. However, the frequency distribution is very heavily skewed, the most frequent class having just three fruiting heads per plant (25%). Each fruiting head contains a mean of 30 achenes, giving a mean total output of 150 ± 10 achenes per flowering plant. When subjected to marked competition, however, R. repens flowering becomes suppressed and, if the plant persists, as it does in some wet habitats, the reproductive balance is even more completely directed towards stolon development, with seed production then becoming meagre or completely absent (Salisbury 1942, p. 226).

Individual plants normally die off after they have successfully fruited, being replaced by a daughter plantlet produced vegetatively on a very short stolon, ie the plant is usually (but not always) monocarpic. This is another example of a biological concept (ie monocarpic versus polycarpic reproduction), which is not absolute, but rather, it is somewhat 'leaky' or facultative in its mode of operation (Forbes 2000, p. 187). The connecting stolons generally (but not always) die off in the autumn from September onwards, leaving the daughter rosettes produced at their nodes as independent plantlets (Van den Berg et al. 1985; Jonsell et al. 2001).

Population studies and plant plasticity and variation

R. repens is one of the best studied weedy plants from a population biology or demographic perspective, having been the subject of major studies by Prof. John Harper and several of his co-workers, including amongst others, Lovett-Doust (1981). The latter showed that Creeping Buttercup populations studied in grassland and open woodland habitats follow similar seasonal patterns. The populations examined remained remarkably stable from year-to-year, but the density of plants in the woodland was significantly greater than that in the particular grassland examined. This suggests that some form of density related self-regulation of population size occurs at a figure referred to as 'the carrying capacity'. The latter varies according to a number of environmental factors. The average time for complete turnover of rosette populations was calculated as 2.17 years for woodland and not significantly different at 2.27 years for grassland rosettes (Lovett-Doust 1981). The creeping habit of the species is a response to the pressure of close grazing (or mowing) and if this is removed the plant will grow more upright (Harper 1957).

The population dynamics of R. repens in pastures in N Wales were examined over a four year period and computer modelled by Soane & Wilkinson (1979). These workers found little evidence of selection among families of clonal rosettes, or against new seedling recruits within populations. Their measurements showed that the number of original genotypes present in a population of R. repens declines continuously at an approximately exponential rate. Local dominance by a few clones is therefore to be expected unless new genotypes are recruited into the population, eg by seedling establishment. There was no evidence that selection was maintaining a diversity of genetic individuals (ie genets) within the R. repens population, but although recruitment of new seedlings was low enough to be described by them as 'occasional', nevertheless it clearly plays a very significant role in the longer term, through determining the number of genets represented in the population, and thus maintaining genetic variation within these populations (Soane & Watkinson 1979).

Variation

Creeping Buttercup is continuously variable in so many of its characters that Coles (1977) found no justification for the distinction of any infraspecific units within the species (ie forms, varieties or subspecies).

Possible allelopathic effect on competing plants

There is a suggestion that R. repens may exert an allelopathic effect (ie a chemical inhibition) when competing with the roots of other plants, possibly involving phenolic compounds (Whitehead et al. 1982). Hatfield (1970) regarded R. repens as responsible for serious depletion of potassium and other elements from soil and he proposed that the roots secrete a toxin causing neighbouring plants to suffer from a nitrogen deficiency (Lovett-Doust et al. 1990). More work is required to clarify the real position on this topic, but as yet nobody has proven that any allelopathic effect exists, although it might be more likely occur in soils rich in lime, or after lime has been applied (Whitehead et al. 1982).

In upland leached acidic soils and in other situations of low fertility, for instance in peat bogs and in wetter, marshy areas, R. repens is much less competitive than in drier, lowland situations and here it tends to be replaced by R. flammula (Lesser Spearwort).

Colonising ability

The immediate opportunistic response of R. repens to disturbed environmental conditions permitting colonisation of new territory tends to be increased stolon development, rather than seedling production. This is thought to be due to stolon production and flowering being largely coincident in May and June, plus the fact that vegetatively produced offspring often do not flower in their first year of growth. However, juvenile plants may do so if the habitat is very open and in these circumstances they generally flower rather late in the season, up until about October (Harper 1957).

On the other hand, seed germination is greatest in late spring, with just a few seedlings appearing in autumn, and then only if there is a combination of high soil temperature and abundant moisture. Germination is very rapid (almost immediate) when seeds are exposed by soil disturbance. Seedlings establish readily where ground is open and particularly when the water table is high but the soil is not completely flooded.

Very rapid colonisation of bare ground may be achieved in the year of germination (Harper 1957). Salisbury (1942, p. 225) illustrates a case where a plant in open garden soil occupied more than 0.5 m² in its first growing season, producing 35 rooting nodes, of which 23 bore inflorescences and twelve remained vegetative. Clearly, this is merely an isolated instance, and growth rate will be dependent upon habitat conditions, but it provides a helpful indication of the level of colonising ability the species is capable of achieving.

Further detail of R. repens population behaviour is present in my R. acris species account under the heading, 'Comparative patterns of population turnover in three buttercups'.

Seed dispersal

No specialised dispersal mechanism exists in R. repens, most of the dry, smooth seed simply being dropped beneath the parent plant. However, cattle and horses are known to help disperse R. repens by transporting the seed in their gut, it having been found in their droppings. Various birds do likewise, notably the House sparrow, but while Partridges, Pheasants and Pigeons are found frequently with a high crop content of R. repens seed, it is unlikely to pass through their guts in a viable condition. Plants growing beside water may disperse seed in flowing streams and occasionally whole plants will dislodge and migrate downstream in the adjacent flow. These processes may possibly be assisted by the disturbing activity of various ducks and water hens (Harper 1957; Salisbury 1964).

Other animals may also act as agents of dispersal, including those which transport propagules externally on their surfaces. This form of dispersal agency includes man and his vehicles. Darlington (1969) found that washings of mud from motor tyres in the month of June contained a considerable number of R. repens achenes. In another novel and unusual, not to say quaint study of the trouser turn-up fluff of schoolboys who walked across fields to school, he showed that of the 70 plant species the boys unwittingly transported, 11% of the propagules were of R. repens (Darlington & Brown 1975). These authors pointed out that with the exception of adherent burrs like those of Galium aparine (Cleavers), the majority of the fruits and seeds in the turn-up are carried loose in the contained dust and fluff, "so that the wearer becomes a sort of peripatetic censer mechanism for scattering propagules, notably the smoother kinds (R. repens and others), as he walks about" (Darlington & Brown 1975, p. 34).

Seed dormancy and survival in soil

Dormancy is enforced by burying the seed and large populations of buried viable seed have been reported. Seed survival ability varies enormously, presumably dependent upon soil moisture, nutrient levels, stability and disturbance.

The survey of soil seed bank of NW Europe tabulates results of no less than 98 records of buried seed survival. Of the four seed bank categories listed, the representation of R. repens appears as follows: transient (surviving less than 1 year) 21; short-term persistent (between 1 and 5 years) 26; long-term persistent (at least 5 years) 30; and present in soil (but not assigned to one of the foregoing) 21 studies (Thompson et al. 1997).

British and Irish occurrence

R. repens is extremely common and widespread over almost all of Britain and Ireland, becoming slightly less frequent in the NW and highlands areas of Scotland (Preston et al. 2002).

World occurrence

It has an almost continuous Eurasian boreo-temperate native range (Jalas & Suominen 1989, Map 1712). R. repens is also introduced and partly naturalised in both N & C America and has thus become circumpolar in its Northern hemisphere distribution. It is also an introduction in South America, South Georgia, New Zealand, Tasmania and Great Barrier Island (Hultén 1971, Map 225; Hultén & Fries 1986, Map 842; Preston & Hill 1997).

Toxicity

Unlike other common buttercup species, R. acris, R. bulbosus and the more scarce R. scleratus (Celery-leaved Buttercup), it appears that Creeping Buttercup in the British Isles normally contains only a low concentration of the Ranunculus poisonous principle protoanemonin (a toxic cardiac glycoside). Consequently, R. repens does not harm stock animals − including horses − and they frequently browse upon it (Cooper & Johnson 1998).

In the wider geographical range of the species however, there are instances where the levels of toxins in populations of R. repens are sufficiently high to make the plant distasteful, or even seriously poisonous, making it capable of causing diarrhoea and abdominal pain in cattle and sheep with symptoms that persist for up to 14 days (Lovett-Doust et al. 1990). In Chile, for instance, in recent times R. repens poisoning was held responsible for causing abortions in a herd of dairy cattle (Morales 1989).

Herbicidal control

Although resistant to a wide range of herbicides, R. repens is very sensitive to translocated selective herbicides such as 2,4-D, MCPA-salt, MCPB-salt, paraquat and aminotriazole (Lovett-Doust et al. 1990). Selective herbicides containing aminopyralid, such as Milestone and VM, can be used to kill Creeping Buttercup. Aminopyralid products such as these are available at farm supply stores and should only be used in areas listed on the label, ie pastures, hayfields and other agricultural settings. Fortunately, aminopyralid products do not harm livestock, provided all precautionary advice is followed. The Nature Conservancy Wildland Invasive Species Team publishes an online Weed Control Methods Handboook that is regularly updated (Tu, M. et al. 2001: http://invasive.org/gist/products/handbook/methods-handbook.pdf

Accessed 25 January 2016). This tabulates herbicide advice and makes recommendations on other ecological manipulations which help limit the weed population. To eradicate Creeping Buttercup from grassland it will probably be necessary to apply herbicide up to three times, since mature plants can often recover, and seed in the soil seed bank will germinate and may re-establish the plant. Sprayed ground will need to be monitored and seedlings removed before they develop runners.

Uses

As R. repens tissues normally contain only a small percentage of protoanemonin, the species has not been used in herbal medicine in the same way as its close relatives, R. bulbosus (Bulbous Buttercup) and R. acris (Meadow Buttercup). In fact, Grieve (1931) does not mention it at all in her comprehensive book, A Modern Herbal.

Names

'Ranunculus' is derived from the Latin 'rana' meaning 'a frog', an allusion to the fact that so many members of the plant genus live in or near water, the habitat of frogs (Johnson & Smith 1946). The Latin specific epithet 'repens' means 'creeping'. As one might expect, R. repens shares many English folk or common names with R. acris. Additional ones include 'Devil's Guts', 'Gold-balls', 'Granny-threads', 'Hod-the-Rake', 'Lantern Leaves', 'Meg-many-feet', 'Ram's Claws', 'Sitfast', 'Sitsicker', 'Tether-Toad' and 'Toad-tether' (Britten & Holland 1886). Many of these names refer to the spreading stolons and/or the tenacity with which its roots cling to the ground, making the plant difficult to eradicate.

Threats

None.

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