Ranunculus aquatilis s.l. L., Water Crowfoot
Account Summary
Native, rare. European temperate.
1884; Barrington, R.M.; Devenish Island, Lower Lough Erne.
May to August.
Growth form and preferred habitats
An annual or short-lived perennial that grows in shallow water in marshes, ponds and ditches and at the edges of slow-moving streams and margins of sheltered lakes. It prefers lowland sites with water that is eutrophic, somewhat base-rich and subject to a moderate degree of disturbance that helps keep the habitat open. These conditions can occur where cattle graze lakeshore margins and water meadows, or pastures around muddy ponds.
Fermanagh occurrence
As emphasised in much of the literature, the heterophyllous and large-flowered water-crowfoot species, R. aquatilis, R. peltatus (Pond Water-crowfoot) and R. penicillatus subsp. penicillatus (Stream Water-crowfoot) are not easily distinguished. This fact should be borne in mind when studying distribution maps of the three species, either ours or anyone else's for that matter matter (Cook 1966a; Preston & Croft 1997; Preston et al. 2002).
Undoubtedly identification difficulty leads to under-recording, and we have only eleven records for R. aquatilis. Since a degree of reasonable doubt hangs over them, we have combined them as s.l. We do not mean to suggest by this that we are considering R. aquatilis s.l. as the old pre-Cook (1966a) species aggregate. However, it is probable that most of the Fermanagh identifications were determined using An Irish Flora (1977) as a field guide. This text used only two features to discriminate this species: flowers between 12 and 17 mm in diameter and floating leaves present in summer. As Cook (1966a) and Webster (1991) have shown, flower size in this species group varies considerably with environmental conditions, and we now appreciate that it is not a reliable distinguishing species character.
Keeping in mind the mentioned reservations, as the tetrad map indicates, the Fermanagh records of R. aquatilis are thinly and widely scattered across ten squares in lowland Fermanagh. Only one record for R. aquatilis pre-dates 1975, that of Barrington (1884), from a wet ditch on Devenish Island. Soon after this record was reported (as R. heterophyllus Fries), Tetley wrote into his copy of Irish Topographical Botany in pencil, "I have no doubt this should be R. peltatus". While only two of the records (Barrington's and one by the NI Lakes Survey) are supported by vouchers in BEL, the eleven records involve at least seven determiners, increasing the probability that some of them are correctly identified. The habitats listed are typical for this species, ie shallow, eutrophic, somewhat base-rich water in lakes, turloughs, rivers, streams and ditches. Further investigation of Batrachian Ranunculi in Fermanagh is very obviously required.
British and Irish occurrence
The distribution map in Preston & Croft (1997) took a more conservative approach to R. aquatilis records than did the editors of the New Atlas (Preston et al. 2002). Recognising that uncertainty still clings to the identification and status of the taxon, the earlier approach is undoubtedly the wiser one. This shows modern records of R. aquatilis extremely thinly scattered throughout Ireland, while the Great Britain distribution displays the plant as more frequent and there are four or more discrete areas of concentration in England and Wales. At the same time, R. aquatilis becomes much rarer and almost entirely coastal in Scotland (Preston & Croft 1997).
European occurrence
R. aquatilis is widespread in Europe from S Scandinavia southwards to the Mediterranean, but while it reaches Sicily, it does not penetrate far into the Iberian Peninsula, or into Greece (Jalas & Suominen 1989, Map 1894).
World occurrence
R. aquatilis s.l. is also found in N Africa, and in the boreal zone it extends across Asia except in the south, plus W and C North America where it also occurs in the alpine zone of the Middle Rockies and southwards into California and New Mexico (Scott 1995, p. 657). It also extends into the southern hemisphere, being present in both western South America (the Andes between 2,700-4,000 m) and SE Australia (Cook 1966a; Jonsell et al. 2001). The world distribution of R. aquatilis is probably second only to that of the closely related species R. trichophyllus (Thread-leaved Water-crowfoot). However, one has to remember that here we are dealing with species which are difficult to identify, and since they are plants which live in disturbed muddy habitats, they are undoubtedly and unwittingly spread by man, so that we do not have much of an idea as to their native ranges (Cook 1985).
Name
The Latin specific epithet 'aquatilis', means 'growing in water' (Gilbert-Carter 1964).
Threats
Shading from competitors and overgrowth by algae and/or other macrophytes due to excessive cultural eutrophication.