It has been shown that not only are some populations of Ranunculus subgenus Batrachium composed of complexes of polyploid clones attributable to a single taxon, but that other populations may be composed more or less entirely of hybrid combinations involving up to three parents and indistinguishable from each other or unhybridised plants without molecular analysis (Lansdown 2007). Several current and conflicting taxonomies (Castroviejo et al. 1986, Stace 1997, Jonsell 2000, Rothmaler 2005, van der Meijden 2005) co-exist and are applied in differing ways in Europe and it is clear from published information that both the identification guidance and recording are inconsistent between countries, regions and taxa.

Assessment of the taxa “most widely recognised” against the Red List Criteria is, at best, hopeful and an attempt has been made to explain any conclusions reached. Distribution data are mainly derived from the only truly critical account (Cook 1966) although it is clear that even that includes some inaccuracies. The exceptions to this are R. circinatus and R. hederaceus which may, at times, be misidentified but are taxonomically discrete.

European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)
 
This species is classed as Least Concern as it is widespread with stable populations and does not face any major threats.

Ranunculus penicillatus is endemic to western Europe, occurring in Estonia, Denmark, Ireland, the United Kingdom, France, Belgium, Germany, the Czech Republic, Italy, Portugal and Spain. Reports of this species from the Balkans, European Russia and other eastern areas are likely to be the result of misidentification (possibly of hybrids) or application of a different taxonomic concept.

Ranunculus penicillatus is a very poorly understood taxon and consequently many reports of presence and abundance are unreliable. Superficially, published evidence would suggest that it is widespread and abundant throughout its range.

Ranunculus penicillatus is almost entirely restricted to flowing water, occurring very occasionally in oxbows and small floodplain pools that have been cut off from the main body of a river, in which it appears to survive for only a short period. It typically occurs in small to medium-sized rivers and streams but will also occur in larger rivers where it may form very extensive stands. It appears to have a broad ecological tolerance occurring in calcareous and acidic waters (although the latter more rarely) and in oligotrophic to mesotrophic or even eutrophic waters.

There are no known past, ongoing or future threats to this species.

This species is categorized Critically Endangered in the Czech Republic (Holub and Procházja 2000).