Crepis foetida L. (syn.: Barkhausia foetida (L.) F.W. Schmidt) (Eur., Macar., SW-As.) – Two more or less distinct subspecies have been recorded in Belgium, only subsp. foetida being native:
1 Outer involucral bracts up to 0,75 mm wide, mostly ca. ½ as long as the inner, with predominantly glandular hairs === subsp. foetida
Outer involucral bracts 1-1,5 mm wide, mostly ca. 2/3 as long as the inner, without or with few glandular hairs === subsp. rhoeadifolia
Subsp. rhoeadifolia (Bieb.) Čelak. (syn.: Crepis rhoeadifolia Bieb., Barkhausia rhoeadifolia (Bieb.) Fisch. et C.A. Mey.) (SE-Eur., SW-As.) – A rare but probably increasing, recently naturalized alien. Discovered in abundance in 2007 on several coal mine heaps in the Kempen (Beringen-Mijn, Zolder, etc.) but probably overlooked before (Verloove 2008). Apparently introduced on the occasion of the remodeling of the coal mine heaps. Some populations of Crepis foetida in the port of Antwerpen also pertain to subsp. rhoeadifolia (e.g. Luithagen, Zandvoort and in this area it is fast spreading lately ). In 2011 also seen on rough ground in Leopoldsburg. Possibly overlooked and confused with subsp. foetida elsewhere.
The Belgian populations of subsp. rhoeadifolia are very typical and readily distinguished from native subsp. foetida (see key; plants are also remarkably tall compared with native specimens). However, in areas where both subspecies are native they easily hybridize and there their separation is much less straightforward.
This taxon is spreading in large parts of Europe, mainly by railway tracks. Even in areas where it was thought to be extinct as a native species it is recently spreading in man-made habitats (Hohla & al. 1998).
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Selected literature:
Babcock E.B. (1938) Crepis foetida and four closely related species. J. Bot., London 76: 202-211.
Babcock E.B. (1947) The genus Crepis. Univ. Calif. Publ. Bot. 21: 1-197, 22: 198-1030.
Babcock E.B. & Cave M.S. (1938) A study of intra- and interspecific relations of Crepis foetida L. Z. Indukt. Abstammungs-Vererbungsl. 75: 124-160.
Hohla M., Kleesadl G. & Melzer H. (1998) Floristisches von den Bahnanlagen Oberösterreichs. Beitr. Naturk. Oberösterreichs 6: 139-301. [available online at: http://www.landesmuseum.at/pdf_frei_remote/BNO_0006_0139-0301.pdf]
Verloove F. (2008) Enkele nieuwe neofyten in België en Noordwest-Frankrijk. Dumortiera 94: 1-8. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_94/Dum%2094_1-8_Nieuwe%20neofyten_Verloove.pdf]