Phacelia Juss.

Phacelia is a taxonomically complex genus with at least 210 species (Walden & al. 2014, Boraginales Working Group 2016). It is mostly native to the western United States. Its center of diversity is in California while some species extend to South America. Rather few species are cultivated as ornamenals (e.g. Cullen 2000, Phillips & Rix 2002, Jäger & al. 2008). A useful overview of alien species is provided by van Ooststroom & Reichgelt (1961). Several additional species have been recorded as aliens elsewhere in Europe, mostly in the British Isles (Clement & Foster 1994).
Recent as well as older molecular data show there is incongruence between nuclear and plastid topologies for the placement of some problematic groups. Further work is needed to understand and compare the rate of molecular and morphological evolution in the genus (Walden & al. 2014).

1 Leaves shallowly toothed. Inflorescence a loose, few-flowered cyme. Corolla bright blue and large, 15-40 mm, with scales absent in throat === Phacelia campanularia
Leaves deeply lobed, to more than halfway to midrib. Inflorescence a multi-flowered dense cyme. Corolla mauve to pale blue, small, 6-10 mm, with scales present in throat === P. tanacetifolia

Additional alien: Phacelia purshii Buckl. (eastern U.S.A., grain alien).


Atwood N.D. (1975) A revision of the Phacelia Crenulatae group (Hydrophyllaceae) for North America. Great Basin Naturalist 35: 127–190. [available online at:

Boraginales Working Group (F. Luebert, L. Cecchi, M. W. Frohlich, M. Gottschling, C. M. Guilliams, K. E. Hasenstab-Lehman, H. H. Hilger, J. S. Miller, M. Mittelbach, M. Nazaire, M. Nepi, D. Nocentini, D. Ober, R. G. Olmstead, F. Selvi, M. G. Simpson, K. Sutorý, B. Valdés, G. K. Walden, M. Weigend). 2016. Familial classification of the Boraginales. Taxon 65(3): 502–522. [available online at:

Brand A. (1913) Hydrophyllaceae. Engler A. (ed.), Das Pflanzenreich, IV,Vol. 251 (Heft 59). Verlag von Wilhelm Engelmann. Leipzig. [available online at:]

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

Constance L. (1949) A revision of Phacelia subgenus Cosmanthus (Hydrophyllaceae). Contributions from the Gray Herbarium 168: 1–48. [available online at:]

Constance L. (1950) Some interspecific relationships in Phacelia subgenus Cosmanthus. Proceedings of the American Academy of Arts and Sciences 78: 135–147.

Constance L. (1953) Howellanthus, a new subgenus of Phacelia. Madroño 11(5): 198–203. [available online at:]

Cullen J. (2000) Phacelia. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 120-121.

Deginani N.B. (1982) Revisión de las especies argentinas del género Phacelia (Hydrophyllaceae). Darwiniana 24: 405–496.

Dempcy J.M. (1996) Phylogenetic relationships in Phacelia section Euglypta (Hydrophyllaceae). M.S. Thesis, San Francisco State University, San Francisco, CA.

Ganong C.K. (2002) Phylogenetic analysis of Phacelia section Miltitzia. M.S. Thesis, San Francisco State University, San Francisco, CA.

Garrison L.M. (2007) Phylogenetic relationships in Phacelia (Boraginaceae) inferred from nrITS sequence data. M.S. Thesis, San Francisco State University, San Francisco, CA.

Gilbert C., Dempcy J.M., Ganong C.K., Patterson R. & Spicer G.S. (2005) Phylogenetic relationships within Phacelia subgenus Phacelia (Hydrophyllaceae) inferred from nuclear rDNA ITS sequence data. Systematic Botany 30: 627–634. [available online at:]

Glass P.M. & Levy F. (2011) Correspondence of morphology, phylogeny, and reproductive barriers in Phacelia subgenus Cosmanthus (Hydrophyllaceae). Journal of the Torrey Botanical Society 138: 341–352.

Halse R.R. (1979) Taxonomy of Phacelia section Miltitzia (Hydrophyllaceae). Ph.D. Dissertation, Oregon State University, Corvallis, OR. [available online at:

Hansen D.R., Spicer G.S. & Patterson R. (2009) Phylogenetic relationships between and within Phacelia Sections Whitlavia and Gymnobythus (Boraginaceae). Systematic Botany 34: 737–746. [available online at:

Heckard L.R. (1960) Taxonomic studies in the Phacelia magellanica polyploid complex, with special reference to the California members. Univiversity of California Publications in Botany 32: 1–126.

Hoffmann M. (1999) Flower and fruit development in the genus Phacelia (Phacelieae, Hydrophyllaceae): characters of systematic value. Systematics and Geography of Plants 68: 203–212.

Howell J.T. (1943a) Studies in Phacelia: a revision of species related to P. pulchella and P. rotundifolia. American Midland Naturalist 29: 1–26.

Howell J.T. (1943b) A systematic study of Phacelia humilis and its relatives in Sertulum Greeneanum. American Midland Naturalist 30: 6–18.

Howell J.T. (1945) Studies in Phacelia: revision of species related to P. douglasii, P. linearis, and P. pringlei. American Midland Naturalist 33: 460–494.

Howell J.T. (1946) A revision of Phacelia section Euglypta. American Midland Naturalist 36: 381–411.

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.

Lee G.J. (1986) Systematic studies in the Phacelia humilis group (Hydrophyllaceae): Corolla venation patterns. American Journal of Botany 73: 230–235.

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.

Phillips R. & Rix M. (2002) Eenjarigen en tweejarigen. Het Spectrum, Utrecht: 288 p.

Sewell M. & Vincent M.A. (2009) Biosystematics of the Phacelia ranunculacea complex (Hydrophyllaceae). Castanea 71: 192–209.

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.

Voss J.W. (1937a) A revision of the Phacelia Crenulata group for North America. Bulletin of the Torrey Botanical Club 64: 81–96.

Voss J.W. (1937b) A revision of the Phacelia Crenulata group for North America (Concluded). Bulletin of the Torrey Botanical Club 64: 133–144.

Walden G.K. (2010) Phylogeny of infrageneric relationships within Phacelia (Boraginaceae) inferred from chloroplast sequence data. M.S. Thesis, San Francisco State University, San Francisco, CA. [available online at:]

Walden G.K., Garrison L.M., Spicer G.S., Cipriano F.W. & Patterson R. (2014) Phylogenies and Chromosome Evolution of Phacelia (Boraginaceae: Hydrophylloideae) Inferred from Nuclear Ribosomal and Chloroplast Sequence Data. Madroño 61(1): 16–47. [available online at:

Walden G.K. & Patterson R. (2012) Nomenclature of Subdivisions Within Phacelia (Boraginaceae: Hydrophylloideae). Madroño 59(4): 211-222. [available online at:

Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith