Ranunculus acris L., Meadow Buttercup
Account Summary
Native, very common and widespread, locally abundant. Eurasian, but widely naturalised in N America, so now circumpolar wide-boreal.
1881; Stewart, S.A.; Co Fermanagh.
Throughout the year.
Growth form
This variable, wintergreen perennial is a widespread and abundant medium-tall herb (up to 50 cm), of moist to seasonally wet (but not waterlogged), pastures, mown meadows and roadside verge grasslands. It is also present in unmanaged grasslands, eg in woodland clearings and on all forms of rock outcrop. Although it possesses a small wintergreen leaf rosette the species produces very little growth until February or March and for its energy requirements the overwintering plant relies on starch stored in its short, stout rootstock (Harper 1957). Coles (1971) refers to the compact rootstock as 'premorse', as opposed to a longer, more spreading, rhizomatous one. The term is derived from the Latin 'praemorsus', meaning 'bitten off', which is a rather appropriate description of the rootstock (Holmes 1979).
Possible native habitats
As with Ranunculus repens (Creeping Buttercup), while fossil evidence proves R. acris is undoubtedly a native species in Britain and Ireland (see below), it is very definitely a 'follower of man'. Nowadays, more often than not it occupies habitats managed, opened up, or created – intentionally or not – by human activity (Harper 1957). It is not really possible to be certain what the natural habitats of R. acris were in these isles prior to human arrival, although Harper (1958) has suggested that it most likely frequented a variety of damp ground communities, ranging from marshes and Carex elata (Tufted-sedge) dominated fens, to mountain grasslands above the climatic forest limit.
Variation
R. acris is a polymorphic species that in Europe can be subdivided into four subspecies (see Flora Europaea 1, Tutin et al. 1993, p. 274), two of which occur in in the British Isles, the common subsp. acris and the much rarer northern subsp. pumilus (Wahlenb.) A. & D. Löve, that only appears in Scotland. R. acris can also be subdivided into three varieties, a larger, very widespread var. acris, a considerably smaller (up to 20 cm tall) var. pumilus Wahlenb. that is restricted to the Scottish Cairngorm mountains, and a hairier var. villosus (Drabble) S.M. Coles, which is common in undisturbed areas of N Scotland (including the isles) and W and C Ireland (Stace 1997, p. 88). Var. villosus was not recorded in Co Fermanagh and certainly is under-recorded across its range.
Soil moisture preferences
The soil moisture preferences of R. acris (although it is not strictly confined to them) are intermediate between those of two other, very common, closely related buttercups, R. bulbosus (Bulbous Buttercup) on drier forms of rocky ground or on shallow soils and R. repens in wetter hollows, or poorly drained soils. Certainly, R. acris is always absent from areas which suffer serious midsummer drought, but thanks to its geographical west Atlantic situation, prolonged drought very rarely, if ever, occurs in Fermanagh (Harper & Sagar 1953; Harper 1957). Meadow Buttercup is taller than these other two mentioned buttercups and thus is better able to compete and survive in the more closed, tightly knit turf of low to moderately fertile, fairly productive, herb-rich water meadows that are such a significant conservation feature of lakeland Fermanagh. These damp, waterside meadows that flood regularly or from time-to-time, harbour some rather aggressive competitive plant species, including the grasses Lolium perenne (Perennial Rye-grass) and Agrostis stolonifera (Creeping Bent) and two even more locally common and dominant herbs than Meadow Buttercup, Juncus effusus (Soft-rush) and Filipendula ulmaria (Meadowsweet).
Fermanagh occurrence
Throughout Fermanagh, R. acris is common everywhere except at the highest, most exposed ground, or in permanently wet, or very acidic habitats. Despite these substrate limitations it is still present in 487 tetrads, 92.2% of those in the VC, making it one of our most widespread species. In terms of tetrad numbers, it ranks fourth equal with Angelica sylvestris (Wild Angelica) and it is the eighth most frequently recorded species in the Fermanagh Flora Database.
Even at this high level of frequency of records, it is possible that our statistics might understate the presence of this species. One of the acknowledged errors in any botanical field survey is the likelihood that very common and familiar plants tend be overlooked, simply because they have become so unremarkable in the recorder's mind, and regularly it will be assumed that they have already been entered on another field recording card and consequently they are overlooked or ignored!
Land management and plant species competition
The farmland grasslands where Meadow Buttercup populations persist to the greatest extent are regularly grazed or mown. This form of ecological pressure is important in maintaining the herb's population size, since without regular disturbance opening up the vegetation and offering periodic temporary release from competitive stress, the species would survive only at much lower frequency. If the grazing or cutting regime becomes relaxed, R. acris cannot thrive and maintain its abundance in the longer term among more vigorous, gregarious and aggressive plant species.
Writing prior to the latest (and greatest) intensification of farming in the last half-century, Harper's (1957) research indicated that the abundance of R. acris in pastures and meadows provides an index of the age of the grassland and that its frequency increased with overgrazing or with regular cropping for hay. Meadow Buttercup has an acrid taste that makes herbivores avoid it and thus it tends to spread and increase in heavily grazed communities (see below for details of its poisonous properties).
The widespread introduction and development of intensively managed 'improved' rye-grass based sown grasslands, replacing old permanent meadows and pastures, together with regular or frequent application of chemical fertilizer or slurry manure, has led to a considerable decline in the abundance of R. acris and, indeed, of most other lowland grassland herbs throughout the British Isles. These forms of government subsidized agricultural 'progress' are aimed at greatly increasing farm productivity and together with other changes in farmland management, eg changing over from arable to grassland farming, improved land drainage operations, swapping from sheep to cattle husbandry and from hay to silage-making, are all practices which have resulted in depletion of plant species diversity on managed land.
Fermanagh has suffered the accumulated effects of these changes along with almost everywhere else in these islands from the second half of the 20th century onwards. The major transformations have been in the more intensively managed productive farmland, which in Fermanagh is most frequently situated in the eastern lowlands. However, where farming has become intensified, drainage generally leads to increased pollution of both surrounding semi-natural ground and adjacent water bodies. This results from inevitable agricultural chemical runoff, both nutrient and toxic. As a result, permanent 'unimproved' pasture has become restricted to less productive ground, either on less accessible steep or rocky slopes, very shallow soils, or in more upland areas featuring small pockets of grazing that are inaccessible to tractors and spraying machinery. Thus, apart from on lightly or occasionally managed lowland wayside grasslands, R. acris is now most frequent and abundant on pastures at higher altitudes, except where such ground becomes excessively acidic (ie below pH 4.0) and nutrient leached, or where grassland gives way altogether to either ericaceous heath or bracken.
British and Irish occurrence
The New Atlas hectad distribution map shows R. acris having almost total cover across Britain and Ireland, the few absences being on exposed western coasts and in a few scattered squares in Irish and Scottish VCs which probably have no resident botanist. In these latter areas, recording even of such a common species inevitably tends to be incomplete, despite the efforts by non-residents. The Relative Change Index of R. acris, measured in Britain (but unfortunately not surveyed in Ireland), between the recording periods of the two BSBI plant Atlases, is calculated as +0.30. The index is interpreted as indicating that R. acris is a stable species in the area studied (Preston et al. 2002).
Buttercup population studies
Detailed demographic studies of field populations of three common buttercup species, R. acris, R. bulbosus and R. repens, were made in the early 1970s at Bangor in N Wales by Dr J. Sarukhan, supervised by Prof. John Harper. Despite its age this pioneering study remains highly recommended reading since the authors thought deeply about plant population processes and used their data, and that of earlier workers, to deduce important generalisations regarding plant behaviour.
Plant ecology has few general concepts that scientists totally agree about, and absolutely no 'Laws' exist as they do in subjects like Physics. However, it is a useful and illuminating exercise to try and generate such general principles whenever possible. Harper and Sarukhan give us a clear picture of the recruitment rate of each buttercup species from seed and also from vegetatively produced daughter plantlets (ie ramets). This fecundity is then compared with the species population mortality and thus the flux or rate of turnover can be calculated (Sarukhan & Harper 1973; Sarukhan 1974, 1976).
The concept of 'a plant population' is an extremely dynamic one, even more so than the concept of 'vegetation', and in the case of the former it involves the gains and losses of individuals happening at the same time. Thus a census approach is essential to population studies, marking and following the fate of individuals, including some that are actively growing and others that may be going through a dormant phase (ie buried viable seeds have also to be considered as part of the total plant species population picture).
Comparative patterns of population turnover in three buttercups
In his research studies, Sarukhan found that individuals of the three common buttercup species had quite different levels of longevity. This reflected their methods of reproduction and the balance of strategy between seed and vegetative ramet reproduction that each employed. Reproduction in R. bulbosus is exclusively by seed, that of R. repens is predominantly vegetative with some seed, and R. acris is mainly seed, but very occasionally it reproduces vegetatively by branching of its characteristic short rhizome.
During the two and a half year period of Sarukhan's study of the three buttercup species, the population flux was greatest in R. acris. Indeed, he found that in some study plots there was no permanent population, only a series of temporary but overlapping short-term cohorts, establishing rapidly from seed and then soon dying. R. acris seed germinated in April and May, with a swift and high mortality peak in May and June, and mortality continued gradually at very low levels until the following spring. A similar picture of high seedling production and mortality occurred in R. bulbosus, although germination in this species took place in the autumn rather than the spring. In both these buttercup species, the high initial seedling mortality is balanced by a long life span for those minority of individuals that manage to survive and become mature established plants.
The high risk of death at the early seedling stage probably reflects not only the very obvious innate risks involved in establishing a viable root and shoot system, but additionally, and probably even more so, the genetic load of unfit genotypes being carried by the species. The new gene combinations that are produced by sexual reproduction are, by their nature, experimental and elimination of the plants with the most unfit genotypes can be expected to occur early in life, as was the case with all three buttercups (Sarukhan & Harper 1973; Sarukhan 1976).
In comparison with the other two buttercups, R. repens (Creeping Buttercup), the only one of the three with appreciable vegetative multiplication, suffers little loss of vegetative individuals (ie ramets) at the very beginning of their life, but it replaces a large number of them more frequently than the other two species do. The life expectancy of a R. repens ramet was short, ranging only between 1.2 and 2.1 years. Very few plants of R. repens derived from seedlings lived for more than 1.5 years, whereas mature plants of both the other buttercups could survive for much longer periods; in the case of R. acris, individuals were shown to live up to eight or more years (Sarukhan & Harper 1973).
R. repens, with its dependable, high level of vegetative reproduction, comparatively weak flowering and seed production, but great seed longevity, contrasted strikingly with the other two buttercup species which had little or no vegetative reproduction, high seed output, rapid germination, high seedling mortality and a rather short half-life of the buried dormant seed (ie just 5 months in the case of R. acris and 8 months in R. bulbosus) (Sarukhan 1974).
Buried seed longevity
Other estimates of buried seed longevity are given in the detailed European survey of this topic published by Thompson et al. (1997). The survey lists a total of 40 estimates for R. acris divided as follows: transient (less than one year) = 19; short-term persistent (between 1 and 5 years) = 10; long-term persistent (at least 5 years) = 3, and present in soil but unassigned to any of these three categories = 8. The equivalent figures for R. bulbosus seed are: 8, 4, 4 and 5 – a total of 21 estimates. It is not unusual for seed longevity estimates to vary, but for both R. acris and R. bulbosus the predominant impression remains that buried seed is relatively short-lived.
Flowering reproduction
Flowering in R. acris stretches from May through to August, peaking in mid-June. Seeds are shed from July onwards. The female flower parts ripen first (ie the flower is protogynous) and a large variety of short-tongued insects visit them to collect nectar, including Honey Bees (Apis mellifera) (Harper 1957). Spatial fragrance patterns within the bowl-shaped flower guide the insect visitor to the nectary, which is partially concealed by a flap at the base of each petal (Bergstrom et al. 1995). Self-incompatibility in the species is described as, "often very marked, but not [occurring] in all populations" (James & Clapham 1935). Although cross-pollination is frequently achieved, some degree of apomixis (ie agamospermy − seed production without any fertilisation or pollen involvement), does occur, perhaps in as many as 1% of flowers (Marsden-Jones & Turrill 1952).
Flowering in R. acris is so very variable in response to its environment that it has proved difficult to measure its flowering capacity. Even Salisbury (1942, 1964), who was very keen to compute such statistics, did not attempt to do so for this species. In his comparative study, Sarukhan (1974) was more daring than Salisbury and in his sample he found that the number of flowers per plant could range from 1-20. Sarukhan also found a high proportion of plants of both R. acris and R. bulbosus each produced between 40 and 140 seeds in total. The maximum seed number produced by an individual plant in his populations was 281 for R acris and 287 for R. bulbosus.
Due to grazing and other forms of disturbance, Sarukhan's study showed that not all plants that flowered managed to set seed, but in R. acris about 40% of flowers did. Over a two year period, similar proportions of R. acris plants flowered in Sarukhan's study, but the ratio of seeds per flowering plant fluctuated wildly, from 26 in 1969, to a little over 1.0 in 1970 (Sarukhan 1974). Since Harper (1957) reported the number of seeds per flower varying between 0 and 40, and the number of flowers per plant was also very variable in his study, the variability helps explain Salisbury's reluctance to measure the reproductive capacity of these buttercup species.
Seed dispersal
As with other buttercups, R. acris has no specialized seed dispersal mechanism, but viable seed has been found in the droppings of birds including the House sparrow (Collinge 1913). Furthermore, Dore & Raymond (1942) calculated from analysis of the seed content of farmyard manure, that a single cow might disperse around 22,000 R. acris seed per ha during a 165 day grazing period. However, as Sarukhan (1974) pointed out, while the seeds are 'dispersed' in this manner, they are also concentrated in 'local droppings'! Voles and Field mice are very probably the main rodent seed predators of Ranunculus species in grasslands in Britain and Ireland, but birds such as Pigeons and Pheasants must also consume and destroy huge quantities of buttercup seed.
Absence of Ranunculus acris hybrids: Hybrids between R. acris and other buttercup species have never been recorded anywhere in Britiain and Ireland, and while crosses with both R. repens and R. bulbosus have been reported from several European countries, Stace (1975, p. 124) regarded them as doubtful and requiring confirmation, and the new Hybrid Flora of the British Isles (Stace et al. 2015) makes no mention of them whatsoever.
Fossil history
Fossil seed (ie achenes) have been found in sediments of the four most recent interglacial periods (from the Comerian onwards) and also from the two most recent glacial stages. This evidence conclusively proves that although R. acris populations increase when human populations disturb natural or semi-natural forms of vegetation, the species very definitely is native in these islands (Godwin 1975).
Toxins
Meadow Buttercup contains the acrid, irritant, poisonous principle protoanemonin, an unstable compound derived from the glycoside ranunculin. The concentration of protoanemonin increases during growth of the plant and reaches a maximum during the flowering period. Being an unstable chemical, however, the drying involved in hay-making readily converts protoanemonin into an inert, non-toxic substance called anemonin and thus dried fodder containing buttercups is perfectly safe to give to animals. Also, R. acris contains much lower toxin concentrations than is found in Bulbous Buttercup (Cooper & Johnson 1998). Due to the presence of this acrid, bitter-tasting toxin, both of these buttercup species are unpalatable when fresh and they are avoided by grazing animals unless the beasts are actually starving (Harper 1957).
R. acris has been known to poison both grazing cattle and sheep, but few cases have been reported in recent years, probably because pastures nowadays contain much smaller proportions of these species than previously was the case for the reasons discussed above (Cooper & Johnson 1998). In Norway in 1988, however, five cows in late pregnancy were turned out to graze on a field of poor pasture containing abundant R. acris. They developed severe diarrhoea, a rapid pulse and noisy respiration and all of them died or had to be destroyed because of their deteriorating condition (Heggstad 1989). Other experimental studies in Canada found that cattle gradually fed increasing amounts of R. acris in the flowering stage could cope very well with between 7 and 25 kg of the plant per day for two weeks towards the end of the experimental trial (Therrein et al. 1962; Hidiroglou & Knutti 1963, both references quoted in Cooper & Johnston 1998).
European and world occurrence
Beyond Britain and Ireland, R. acris s.l. (ie the polymorphic species we are considering here) is common over the whole of C and N Europe including the Faeroes and Iceland. There is some dispute as to whether or not it is native in Greenland, since material from there was indistinguishable from plants known to have been definitely introduced to Spitzbergen and N America (Coles 1971). R. acris has a more limited distribution in S Europe; it is absent from Portugal and areas S of latitude 40oN (Jalas & Suominen 1989, Map 1714). The coverage of the species in Italy was under-recorded by the latter map, since Pignatti (1997, 1, p. 306) maps a complete cover of the peninsula. R. acris is also found in Morocco, and while it is very rare on Madeira, it is absent from all of the Canaries (Hultén 1971, Map 288; Press & Short 1994).
R. acris is very widely naturalised across the world and as a result has become circumpolar in the N Hemisphere (Hultén & Fries 1986, Map 844; Preston & Hill 1997). It is also introduced in a few temperate areas of the S Hemisphere, eg in S Africa and New Zealand (Hultén 1971; Hultén & Fries 1986).
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 'acris' means 'acrid', ie with a sharp, burning, peppery taste (Gilbert-Carter 1964). This is very descriptive of all parts of the plant. Contact with skin can cause severe blistering (Grieve 1931; Cooper & Johnston 1997). Despite this, the caustic sap has been used in herbal medicine to remove warts and the plant has also been used to treat headache, gout and even cancer (Grieve 1931). As ever, a health warning should here be attached to these comments and no recommendation whatsoever is intended or implied by the inclusion here of this information.
The English common names include a recognition of the danger of handling the plant, eg 'Blister cup' and 'Blister plant' are both listed by Grigson (1987). Britten & Holland (1886) provide a list of 38 varied common names including 'Clovewort', 'Crowflower' and 'Bassinet'. The latter name means 'a small basin', apparently a reference to the bowl shape of the flower and, therefore, quite widely applied to a whole range of flowers, including all species of buttercup, Caltha palustris (Marsh-marigold) and many Geranium species. 'Crowflower', 'Crowfoot' and other versions of this name, refer to the deeply cut leaf shape of many buttercup species and their relatives plus, again, some species of Geranium, eg G. pratense (Meadow Crane's-bill) (Grigson 1974). Other common names refer to the gold or yellow flower colour, but the strangest name of all appears to be 'Crazy' (see below in the species synopsis of Ranunculus repens) (Prior 1879).
Threats
None. R. acris is readily exterminated by modern systemic herbicides and the species has only a negligible, short-lived, soil seed bank. It has survived for thousands of years despite these limitations.