Potentilla intermedia L. (incl. P. heidenreichii Zimm., P. digitato-flabellata A. Braun et Bouché) (E Eur., N As.) – A rather rare but increasing, locally naturalized alien. Already known in 1818 in the Verviers area. However, the species’ genuine naturalization only started at the end of the 19th century when it was already abundantly and repeatedly recorded around Visé (borders of river Meuse) since 1891 and in Modave (abandoned quarries in the valley of river Hoyoux since 1887). Other cases of early naturalization / long time persistence were documented from Aarschot (since 1936), Anderlecht (since 1943), Boitsfort (since 1946), Ekeren (Oude Landen; since 1912), vicinity of Genk (coal mining spoil heaps since 1967), Hechtel-Leopoldsburg (since 1959), Leuven (since 1920), Brecht (Groot Schietveld; since 1957, along with P. norvegica but less frequent than the latter), etc. In the Borinage area, where P. intermedia is common these days, it is known from several different localities since at least 1911. At present P. intermedia is well-naturalized in Belgium but it is not uniformly distributed: in Flanders it is much more frequent in the Kempen and in and around the larger agglomerations (mostly Antwerp, Brussels and Ghent) (Van Landuyt 2006). In the western part of our territory it is much rarer (Verloove 2002). In Wallonia P. intermedia is more evenly distributed (and perhaps less rare).
Its vector of introduction is not always clear. In the past it was associated with the wool processing industry around Verviers (recorded there at least between 1818 and 1921), while more recent records are sometimes related to grain importation.
Potentilla intermedia mostly grows in various kinds of man-made habitats, preferably in dry and sunny conditions: by railway tracks, on coal mining spoil heaps, in abandoned quarries, etc. However, it is also locally naturalized in more natural environments, for instance in heath lands (e.g. nature reserve Groot Schietveld), on exposed pond margins, etc.
Potentilla intermedia is believed to be a stabilized hybrid of P. argentea / P. norvegica parentage; this was recently experimentally confirmed by Soják (2012). P. heidenreichii is sometimes segregated from P. intermedia, especially by eastern European taxonomists. It has hairier and smaller leaves and seems to be a transitional species between Potentilla inclinata and P. intermedia. However, an analysis of macro- and micromorphological variables shows a rather weak distinction between both species (Leht & Paal 1998). Moreover, according to Soják (2009) leaf indumentum in Potentilla intermedia is extremely variable and this species is best distinguished on measurements of floral parts (petals, anthers). Moreover, Potentilla heidenreichii is of the same parentage (P. argentea x norvegica; Soják 2012). In Ball & al. (1968) Potentilla intermedia fails to key out: it is erroneously said to have accrescent sepals and epicalyx segments (dichotomy 69), a characteristic feature of P. norvegica.
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Selected literature:
Asker S. (1970) Apomictic biotypes in Potentilla intermedia and P. norvegica. Hereditas (Lund) 66: 101-107.
Ball P.W., Pawłowski B. & Walters S.M. (1968) Potentilla. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 2. Cambridge University Press, Cambridge: 36-47.
Ertter B., Elven R., Reveal J.L. & Murray D.F. (2014) Potentilla. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 9. Oxford University Press, New York-Oxford: 121-218. [available online at: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=126635]
Jonsell B. & Jarvis C.E. (2002) Lectotypification of Linnaean names for Flora Nordica (Brassicaceae - Apiaceae). Nord. J. Bot. 22(1): 67-86.
Leht M. & Paal J. (1998) Potentilla L. sect. Rivales Wolf and related taxa in the Baltic States. Folia Geobot. 33: 171-186.
Saintenoy-Simon J., Godefroid S. & Verhelpen B. (1995) Groupe Flore Bruxelloise. Notes floristiques relatives à la Région de Bruxelles-Capitale (1991-1993). Adoxa 6-7: 27-37.
Shetler S.G. (1958) A taxonomic study of the relationships of Potentilla intermedia L.
Soják J. (2009) Potentilla L. (Rosaceae) in the former USSR; second part: comments. Notes on Potentilla XXIV. Feddes Repert. 120(3-4): 185-217.
Soják J. (2012) Copies of seven species and twenty hybrids of Potentilla (Rosaceae) obtained through experimental hybridization (Notes on Potentilla XXVI.). Thaiszia 22(1): 33-48. [available online at: http://www.upjs.sk/public/media/7803/033-048-sojak-upr.pdf]
Van Landuyt W. (2006) Potentilla intermedia. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de flora van Vlaanderen en het Brussels gewest. Instituut voor Natuur- en Bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 707.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.