There are no significant taxonomic issues associated with this name.

European regional assessment:  Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

This species is classed as Least Concern because, although there is no reliable evidence of a decline, its EOO exceeds 20,000 km², its AOO exceeds 2,000 km² and it is known from at least 140 sites. However, it is apparently critically dependent upon traditional fish pond management practices and as a result is vulnerable to a single change in management practice.

Coleanthus subtilis has a curiously patchy distribution, it occurs from western France through much of central Europe, western Siberia, the Russian Far East and northeastern China and a small area on the border of Washington and Oregon States in western North America where it may be non-native. In Europe, it occurs in Brittany (France), scattered sites in Germany, Austria, the Czech Republic, Slovakia, Poland and northern Italy. In Norway, Coleanthus subtilis is treated as an adventive species, which was probably spread by birds. It was sampled in the years 1837-1842 and has probably not been reproducing in Norway at any length of time and at least not in the last 150 years (Å. Viken pers. comm. 2010).

Population estimations:
In France, it is rare and found in four departements: Côtes d’Armor (pools of Coroncq and Rochevel), Morbihan (pools of Duc, Vaulaurent), Ille-et-Vilaine (pools of Trémignon, Bourg à Hédé, Comper, Abbaye, Forges, Rouvre), and Loire-Atlantique (pools of Vioreau, Grand-Auverné, Villate) (Bensettiti et al. 2002).

In Austria, the species was classed as possibly extinct for several years until it was rediscovered in the year 2000. This triggered research into soil seed banks and the viable seeds of the species have been found. It is currently found at five sites with mature individuals (Bernhardt 2005a,b; Bernhardt et al. 2005).
It was reported from 120 localities in the Czech Republic. But this often refers to one pond and in some regions there are five to ten ponds in one hectare (K.-G. Bernhardt pers. comm. 2010).

In Poland, it can be found at one site in a complex of fishponds in Borowa, near Wrocław, where the species is found in four ponds in a total area of 15 ha. The population occurs at the bottom of emptied ponds and the number of individuals fluctuates depending on the fishpond management cycle (Kalinka and Nowak 2004).

In Germany, it is found in the Erzgebirge (Ore mountains) in southeast Germany, in Sachsen-Anhalt along the river Elbe, and in Rheinland Pfalz (Bundesamt für Naturschutz 2010, Hardtke and Ihl 2010).

There is no detailed information for other countries in Europe. Whilst there has been suspicion of a decline, in fact the number of sites supporting C. subtilis has increased in recent years, whilst the discovery of strong seed-banks in areas where the species had been thought extinct is extremely encouraging.

C. subtilis occurs in two locations in the Novgorod region of northwest Russia and in the Volga region of southern Russia where it has apparently undergone a very rapid decline. However, it is known to show massive inter-annual fluctuations in population size (I. Illarianova pers. comm. 2010).

In Europe, C. subtilis is a characteristic species of the drawdown zones of fish ponds, elsewhere it occurs on muddy stream and lake margins and other wet, open habitats. It is a pioneer species and a weak competitor.
It is found in habitat number 3130 "Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea" of the Habitats Directive (Commission of the European Communities 2009).
A study by Bernhardt et al. (2004) demonstrated that even where a species was declared extinct, seeds can still be stored in the soil banks for a long time. Germination tests of seeds from soil samples in former localities showed those seeds to be viable. In most cases they need fluctuating water levels to trigger germination and a stabilisation of the water levels has led to local extinctions of mature individuals.

The main threats to the species are changes to the hydrological regime of the water bodies where it is found. This species needs fluctuating water levels and stabilisation of these leads to its disappearance or at least to a reduction of the area where it can develop. Other threats are the application of pesticides or fertilisers, a high input of nutrients (for example to feed fish) and water pollution. The species is not a good competitor and therefore sensitive to changes of surrounding vegetation. The removal of sediment at pool edges is another threat as it affects the soil seed bank.

This species is listed on Annex II of the Habitats Directive and under Appendix I of the Convention on the Conservation of European Wildlife and Natural Habitats (Bern Convention).

C. subtilis is listed as Critically Endangered in Austria and Italy, Endangered in the Czech Republic, Vulnerable in Germany and France and is protected at a national level in the latter two countries as well. It is categorized as Critically Endangered in Russia (I. Illarionova pers.comm. 2010).

Ex situ conservation of the seeds in gene banks is taking place (Bernhardt et al. 2008). To conserve the species, it is necessary to manage its sites in a way that allows fluctuating water levels. Monitoring of the populations is strongly recommended.