Dipsacus strigosus found in Belgium and possibly overlooked

Dipsacus is a genus of ca. 15 Old World species, mainly distributed in Eurasia and the Mediterranean region (some in Africa and Asia). All species are more or less alike. However, a few are distinguished by shortly petiolate cauline leaves (not sessile and connate as in most other species) and globose flower heads. These are sometimes segregated as a distinct genus, Virga Hill. (see for instance Štepánek & Holub 1997) but this point of view is not followed by other recent taxonomists nor is it supported by molecular phylogenetic studies. From this group, one species is native in Belgium, Dipsacus pilosus L. (syn.: Virga pilosa (L.) Hill). It was initially restricted to a rather small area in Wallonia (mainly on calcareous substrate) with some additional local occurrences in Flanders (van Rompaey & Delvosalle 1979). However, in the past decades it considerably increased, both in Flanders and in Wallonia (Van Landuyt 2006). A very similar species, Dipsacus strigosus Willd. ex Roem. et Schult. (syn. Virga strigosa (Willd. ex Roem. et Schult.) Holub), a native of southern Russia and Ukraine, is known from several different western and Central European countries (see Ahrens 2008 for an extensive overview of its naturalisation history in Europe; see also Poelt 1970, Leslie 1980, Helfrich & Lohwasser 1990, Walter 2004, Ahrens 2007, etc.). Like Dipsacus pilosus it is much increasing lately and its occurrence in Belgium was long-awaited. In fact, part of the recent, more or less disjunct Belgian records of Dipsacus pilosus may well refer to D. strigosus. Indeed, in July 2012 Dipsacus strigosus was finally recognized in Belgium as well, apparently for the first time. In this short account its distinguishing features are discussed and compared with Dipsacus pilosus. Some photos from its unique Belgian locality are also provided.

On the 6^th of July 2012 a small but clearly established population of Dipsacus strigosus was discovered by a riverlet in woodland in Jette (Brussels, Koning Boudewijnpark). The species grows among fairly trivial native species such as Carex pendula, Circaea lutetiana, Cirsium oleraceum, Heracleum sphondyllium, Lythrum salicaria, Rumex sanguineus, Symphytum officinale, etc. Nearby are some plants of introduced Telekia speciosa. The origin of this population of Dipsacus strigosus is obscure: the locality now is a park but it obviously lies in old woodland. Some species are doubtlessly introduced on purpose, for instance Epimedium spec. and Geranium macrorrhizum. Dipsacus strigosus is a rather weedy species and not really appropriate as an ornamental. It is not widely cultivated in Europe according to Matthews (2000) and Jäger & al. (2008). However, British records are considered to be escapes from botanical gardens (Clement & Foster 1994).

Dipsacus strigosus is much reminiscent of D. pilosus. Their most important distinguishing features are opposed in the table below.

In addition, Dipsacus strigosus often is larger in all its parts and its achenes tend to be more smooth. Distinguishing features of both species are very beautifully illustrated by Ahrens (2007).

Belgian botanists are encouraged to look out for this lookalike. Especially records of “Dipsacus pilosus“ from unusual habitats (wasteland, …) or disjunct areas are possibly suspect and require further investigation.

References

Ahrens W. (2007) Zur Unterscheidung von Dipsacus pilosus L. und Dipsacus strigosus Willdenow ex Roemer et Schultes. Mitt. Florist. Kart. Sachsen-Anhalt 12: 71-75. [Available online at: http://www.bv-st.de/images/Flo-Kart_2007_071-075_Ahrens.pdf]

Ahrens W. (2008) Dipsacus strigosus Willdenow ex Roemer et Schultes 1818. Eine neue Sippe in Niedersachsen. Braunschw. Geobot. Arb. 9: 21-41. [available online at: http://rzbl04.biblio.etc.tu-bs.de:8080/docportal/servlets/MCRFileNodeServlet/DocPortal_derivate_00012649/Ahrens_Dipsacus_strigosus.pdf]

Clement E.J. & Foster M.C. (1994) Alien plants of the British Isles. BSBI, London: XVIII + 590 p.

Helfrich T. & Lohwasser W. (1990) Zur Verbreitung der Behaarten Karde (Dipsacus pilosus L.) und der Schlanken Karde (Dipsacus strigosus Willd. ex Roemer et Schultes) in Oberfranken. Ber. Naturforsch. Ges. Bamberg 65: 25-61.

Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.

Leslie A.C. (1980) Further records of Dipsacus strigosus Willd. in Cambridgeshire. Watsonia 13: 126-128.

Matthews V.A. (2000) Dipsacus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 456-457.

Poelt J. (1970) Dipsacus pilosus und sein verkannter Doppelgänger Dipsacus strigosus in Südbayern. Ber. Bayer. Bot. Ges. 42: 203-206.

Štepánek J. & Holub J. (1997) Virga and Dipsacus. In: Slavík B. (ed.), Kvetena Ceské Republiky, vol. 5. Academia, Praha: 529-532 and 532-535.

Van Landuyt W. (2006) Dipsacus pilosus. 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: 345.

Van Rompaey E. & Delvosalle L. (1979) Atlas de la flore belge et luxembourgeoise. Ptéridophytes et Spermatophytes (2^ième éd.). Jardin Botanique National de Belgique, Meise: 1542 cartes.

Walter E. (2004) Über die Ausbreitung der schlanken Karde (Dipsacus strigosus Willd. ex Roemer et Schultes) in Oberfranken. Flor. Rundbr. 38(1-2): 81-86.

Filip Verloove, July 2012