Phacelia tanacetifolia Benth. (western U.S.A.) – A rather frequent but always ephemeral alien. Apparently first collected in 1884 near Visé and Herstal (waste land, road verge). Subsequently seen in numerous, very scattered locations. In the past decades probably increasing. Nowadays frequently sown as a set-aside crop, green manure or to deter eelworms (formerly also by bee-keepers). Phacelia tanacetifolia is usually found along road verges, on waste land, sand rised sites or on dumps.
Some very similar species might have been overlooked, especially Phacelia distans Benth. (see van Ooststroom & Reichgelt 1961). Phacelia congesta Hook. is sometimes included in annual seed-mixtures. It is slightly smaller in all floral parts and less hirsute than P. tanacetifolia. P. ciliata Benth. has repeatedly been recorded as grain alien in the British Isles (Stace 2010).
Sowings of Phacelia tanacetifolia are sometimes contaminated by other, closely related species (see Lienenbecker 1984).
Selected literature:
Havrenne A. (1997) Phacelia tanacetifolia Benth., nouvelle plante de culture et adventive en voie d’expansion. Adoxa 15-16: 15-16.
Kaul M.K. (1972) Two new plant records for India from Kashmir. J. Bombay Nat. Hist. Soc. 69(1): 229-230.
Lead S. (1997) Phacelia tanacetifolia as 'green manure'. BSBI News 75: 40-44. [available online at: http://archive.bsbi.org.uk/BSBINews75.pdf]
Lienenbecker H. (1984) Pflanzen, von denen in der Mitteleuropäischen Literatur selten oder gar keine Abbildungen zu finden sind. Folge XVII – Phacelia viscida Benth. Gött. Flor. Rundbr. 18(1/2): 27-28.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Van Ooststroom S.J. & Reichgelt Th.J. (1961) Boraginaceae. In: van Ooststroom S.J. & al. (eds.), Flora Neerlandica, vol. 4(1). KNBV, Amsterdam: 92-140.
Walter E. (1980) Phacelia tanacetifolia Benth.: Wiederaufleben des Anbaues in Oberfranken. Ber. Naturforsch. Ges. Bamberg 54: 62-68.