Polemonium L.
Polemonium is a genus with ca. 25 species in the Northern hemisphere, the majority being native to North America. Three species are native in Europe (Tutin 1972) but none in Belgium. About ten species are grown as ornamentals in gardens (e.g. Nicol-Brown 2000, Jäger & al. 2008) although probably only one is widely available, P. caeruleum L. It has escaped from cultivation in Belgium as well. Several additional species, some closely related to P. caeruleum, have been recorded in the British Isles (Clement & Foster 1994).
Molecular studies confirmed three species complexes within the genus, one of them being the Polemonium caeruleum group (Worley et al. 2009).
Literature
Clement E.J. & Foster M.C. (1994) Alien plants of the British Isles. BSBI, London: XVIII + 590 p.
Davidson J. F. (1950) The genus Polemonium [Tournefort] L. University of California Publications in Botany 23: 209–282.
Grant V. (1989) Taxonomy of the tufted alpine and subalpine Polemoniums (Polemoniaceae). Botanical Gazette 150: 158–169.
Ito K. (1972) Polemonium in Hokkaido, the Kuriles and Sakhalin: 1 (in Japanese). J. Geobot. 20(4): 91-93.
Ito K. (1983) Polemonium in Hokkaido, the Kuriles and Sakhalin. Environ. Sci., Hokkaido 6(2): 247-280.
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.
Mathewes RW. (1979) Pollen morphology of Pacific Northwestern Polemonium species in relation to paleoecology and taxonomy. Canad. J. Bot. 57(21): 2428-2442.
Moe D. (2001) Contribution to the flora history of the genus Polemonium with special reference to north Norway. Grana 40(6): 292-298. [available online at: http://www.tandfonline.com/doi/pdf/10.1080/00173130152987526]
Nicol-Brown D. (2000) Polemonium. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 101-104.
Ostenfeld C.H. (1929) Genetic studies in Polemonium. Hereditas 12: 33–39.
Pritchett D. (1993) A biosystematic study of California alpine Polemoniums. Fremontia 21(2): 24-26.
Pritchett D.W. & Patterson R. (1998) Morphological variation in California alpine Polemonium species. Madroño 45: 200–209.
Timme R.E. (2001) A molecular phylogeny of the genus Polemonium (Polemoniaceae). M.S. Thesis. San Francisco, CA: San Francisco State University.
Tutin T.G. (1972) Polemonium. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 3. Cambridge University Press, Cambridge: 74.
Wherry E.T. (1942) The genus Polemonium in America. American Midland Naturalist 27: 741–760.
Wherry E.T. (1967) Our temperate tufted Polemoniums. Aliso 6: 97–101. [available online at: https://pdfs.semanticscholar.org/1327/1fe9f1eb3e268b09b18526338db169cc33...
Worley A.C., Ghazvini H. & Schemske D.W. (2009) A Phylogeny of the Genus Polemonium Based on Amplified Fragment Length Polymorphism (AFLP) Markers. Syst. Bot. 34(1): 149-161. [available online at: https://www.researchgate.net/profile/Douglas_Schemske/publication/233700...
Zimmerman M. (1984) Reproduction in Polemonium: a five year study of seed production and implications for competition for pollinator service. Oikos 42(2): 225-228.