thesiumThesium arvense Horv.
- Occurrence in Alberta – Yes
- Haber, Upland – No
- Haber, Wetland – No
- CWF, Status & Invasive Range – No
- Alberta Revegetation Guidelines – No
- AB Weed – No
This species was first discovered in Fish Creek Provincial Park on July 19, 2001 by during a Nature Calgary botany field trip. It was subsequently identified by Doug Waylett. (Gus Yaki, pers. comm. to Ian Macdonald). It was identified independently by Susanne Visser of the University of Calgary for the May Species Count in 2005, who noted that this was a species new to Canada. This is a genus with many species that occur world-wide, and this species is considered to be a weed in Europe. Its only other reported locations in North America are North Dakota and Montana (NatureServe 2010).
Within Alberta it is known only from two locations in Calgary (Yaki, pers. comm. to Ian Macdonald), and Fish Creek Provincial Park has the greater number. In 2005, G. Yaki had two locations, and I.D. Macdonald had an additional 19 known locations in the park, all but one south of Fish Creek on the valley basin, slopes and crest between the line of 24 Street SW and eastward to the bluff crests north of Evergreen Estates.
Investigations in 2009 discovered 4 additional sites in the valley basin on the north side of Fish Creek between Votier’s Flats and Macleod Trail, north of the creek just east of the line of Acadia Drive, and in the vicinity of the park entrance gate off Bannister Road.
Gus currently (Jan. 2011) reports that it has now been seen in hundreds of location - open, sunny sites - within Fish Creek Prov. Park from 37 St SW to the Bow River.
As of Feb 2013, Ian reports that it has been found in the Cross Conservancy SW of Calgary and on the other side of the Bow River from Fish Creek.
Another species, T. chinense Turcz. (百蕊草 bai rui cao, or "numerous pistil grass") is used in Chinese medicine and may be cultivated on a small scale in North America. It has not been reported naturalized, according to USDA Plants. It is a smaller plant. The perianth is tubular (not campanulate) with acute or acuminate lobes that are incurved (not reflexed).
Macdonald, Ian D. 2009. Fish Creek Provincial Park, Calgary Alberta: Vascular Plant Flora And Collections - 2009.
Yaki, G. and Ian D. Macdonald. 2003. Thesium arvense in Fish Creek Provincial Park (Slideshow from which Ian's photos have been copied above).
 USDA Plants Database.
 eFloras.org description of T. arvense from Flora of China.
 eFloras.org description of T. chinense from Flora of China.
 illustration of T. chinense from eFloras.org with contrasting details of other species including T. arvense.
 BioLib.cz image and additional information.
Atlas Florae Europaeae: Distribution of vascular plants in Europe. II. Salicaceae to Balaophoraceae 4. Polygonaceae 5. Chenopodiaceae to Basellaceae, Volume 3, Cambridge University Press, 1987. (Distribution in Western and Eastern Europe).