Phacelia, the phacelias or scorpionweeds, is a large plant genus. It contains about 200 species of herbs, native of Western North America (the most), Eastern USA and South America.
The genus is traditionally placed at family rank with the waterleaves (Hydrophyllaceae) in the order Boraginales. The Angiosperm Phylogeny Group, recognizing that the traditional Boraginaceae and Hydrophyllaceae are paraphyletic with respect to each other merges the latter into the former and considers the family basal in the Euasterids I clade. Other botanists continue to recognize the Hydrophyllaceae and Boraginales, but to make them monophyletic the present genus be moved to the Boraginaceae.
Many species are cultivated as garden plants and for honey plant.
Contact with some species of Phacelia can cause a very unpleasant rash similar to that from poison oak and poison ivy in sensitive individuals. The major contact allergen of Phacelia crenulata has been identified as geranylhydroquinone.
- (2005): Phylogenetic Relationships within Phacelia subgenus Phacelia (Hydrophyllaceae) Inferred From Nuclear rDNA ITS Sequence Data. Systematic Botany 30(3): 627-634.
- (2001): Secondary structure of the ITS1 transcript and its application in a reconstruction of the phylogeny of Boraginales. Plant Biology 3: 629–636.
- (2000): The phylogeny of the Asteridae sensu lato based on chloroplast ndhF gene sequences. Mol. Phylogenet. Evol. 16: 96–112.