Navarretia is one of the larger genera in Polemoniaceae and counts ca. 35-40 species, depending on species delimitation (Johnson & al. 2012, Johnson & al. 2016). All are native to western North America, Argentina and Chile. The genus’ center of diversity, however, obviously is in California. A taxonomic account and an updated key to the Californian species of Navarretia are available online at: http://ucjeps.berkeley.edu/cgi-bin/get_IJM.pl?key=8874.
Many of the species of Navarretia have a relatively or even very local distribution. A few species, however, are more widespread and one, N. squarrosa (Skunkweed), occurs as a weed in many parts of the world, including Belgium.
Johnson L.A., Chan L.M., Burr K. & Hendrickson D. (2012) Navarretia furnissii (Polemoniaceae), a new diploid species from the intermountain western United States distinguished from tetraploid Navarretia saximontana. Phytotaxa 42: 51-61. [available online at: https://biotaxa.org/Phytotaxa/article/view/phytotaxa.42.1.7/17343]
Johnson L.A., Gowen D., Johnson R.L., Brabazon H. & Goates E.D. (2016) Navarretia crystallina and N. miwukensis (Polemoniaceae): new species endemic to California with affinity for soils derived from pyroclastic deposits. Phytotaxa 257(3): 249-260. [available online at: https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.257.3.3]
Spencer S.C. & Porter J.M. (1997) Evolutionary diversification and adaptation to novel environments in Navarretia (Polemoniaceae). Systematic Botany 22: 649–668. [available online at: https://www.researchgate.net/profile/J_Porter4/publication/273238399_Evo...