Phacelia (phacelia, scorpionweed, heliotrope) is a genus of about 200 species of annual or perennial herbaceous plants in the family Hydrophyllaceae, native to North and South America. California is particularly rich in species with over 90 recorded in the region.

The genus includes both annual and perennial species. Many have been cultivated as garden and honey plants.

The mining bee Andrena phaceliae is a specialist pollinator of this genus in the Eastern United States.

Taxonomy: The genus is traditionally placed at family rank with the waterleafs (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 after analysing the secondary structure of the ITS1 genetic region rather than its sequence for these higher taxonomic levels. This placed Phacelia within the Hydrophyllaceae. Further molecular taxonomic analysis of the Boraginales has divided the Boraginales in two and placed Phacelia among the monophyletic herbaceous Hydrophyllaceae in Boraginales II. , this placement was accepted by World Flora Online, among other taxonomic databases.

Selected species: 

• Phacelia adenophora – glandular yellow Phacelia
• Phacelia affinis – limestone Phacelia
• Phacelia anelsonii – Aven Nelson´s Phacelia
• Phacelia argentea – sand dune Phacelia
• Phacelia argillacea – Attwood´s Phacelia, clay Phacelia (endangered)
• Phacelia austromontana – Southern Sierra Phacelia
• Phacelia bicolor – trumpet Phacelia
• Phacelia bolanderi – Bolander´s Phacelia
• Phacelia brachyloba – shortlobe Phacelia
• Phacelia breweri – Brewer´s Phacelia
• Phacelia californica – California Phacelia
• Phacelia calthifolia – Caltha-leaved Phacelia
• Phacelia campanularia – California bluebell, desertbells
• Phacelia cicutaria – caterpillar Phacelia
• Phacelia ciliata – Great Valley Phacelia
• Phacelia coerulea – skyblue Phacelia
• Phacelia congdonii – Congdon´s Phacelia
• Phacelia cookei – Cooke´s Phacelia
• Phacelia corymbosa – serpentine Phacelia
• Phacelia covillei – Coville´s Phacelia, buttercup scorpionweed
• Phacelia crenulata – notch-leaved Phacelia, Cleftleaf wild heliotrope
• Phacelia cryptantha – hiddenflower Phacelia
• Phacelia curvipes – Washoe Phacelia
• Phacelia dalesiana – Scott Mountain Phacelia
• Phacelia davidsonii – Davidson´s Phacelia
• Phacelia distans – distant Phacelia
• Phacelia divaricata – divaricate Phacelia
• Phacelia douglasii – Douglas´ Phacelia
• Phacelia egena – Kaweah River Phacelia
• Phacelia eisenii – Eisen´s Phacelia
• Phacelia exilis – Transverse Range Phacelia, lavender windows
• Phacelia fimbriata – fringed Phacelia
• Phacelia floribunda – San Clemente Island Phacelia, Southern Island Phacelia
• Phacelia formosula – North Park Phacelia (endangered)
• Phacelia fremontii – Frémont´s Phacelia
• Phacelia grandiflora – largeflower Phacelia
• Phacelia greenei – Scott Valley Phacelia
• Phacelia grisea – Santa Lucia Phacelia
• Phacelia gymnoclada – nakedstem Phacelia
• Phacelia hastata – silverleaf Phacelia
• Phacelia humilis – low Phacelia
• Phacelia hydrophylloides – waterleaf Phacelia
• Phacelia imbricata – imbricate Phacelia
• Phacelia insularis – coast Phacelia
• Phacelia inundata – playa Phacelia
• Phacelia inyoensis – Inyo Phacelia
• Phacelia ivesiana – Ives´ Phacelia
• Phacelia lemmonii – Lemmon´s Phacelia
• Phacelia leonis – Siskiyou Phacelia
• Phacelia linearis – threadleaf Phacelia
• Phacelia longipes – longstalk Phacelia
• Phacelia malvifolia – stinging Phacelia
• Phacelia marcescens – persistentflower Phacelia
• Phacelia minor – Whitlavia, wild Canterbury bells
• Phacelia mohavensis – Mojave Phacelia
• Phacelia monoensis – Mono Phacelia
• Phacelia mustelina – weasel Phacelia, Death Valley round-leaved Phacelia
• Phacelia mutabilis – changeable Phacelia
• Phacelia nashiana – Charlotte´s Phacelia
• Phacelia neglecta – alkali Phacelia
• Phacelia nemoralis – shade Phacelia
• Phacelia orogenes – mountain Phacelia
• Phacelia pachyphylla – blacktack Phacelia
• Phacelia parishii – Parish´s Phacelia
• Phacelia parryi – Parry´s Phacelia
• Phacelia pedicellata – pedicellate Phacelia
• Phacelia perityloides – Panamint Phacelia
• Phacelia phacelioides – Mt. Diablo Phacelia
• Phacelia platyloba – broadlobe Phacelia
• Phacelia pringlei – Pringle´s Phacelia
• Phacelia procera – tall Phacelia
• Phacelia purpusii – Purpus´ Phacelia
• Phacelia purshii – Miami mist
• Phacelia quickii – Quick´s Phacelia
• Phacelia racemosa – racemose Phacelia
• Phacelia ramosissima – branching Phacelia
• Phacelia rattanii – Rattan´s Phacelia
• Phacelia rotundifolia – roundleaf Phacelia
• Phacelia saxicola – stonecrop Phacelia
• Phacelia sericea – silky Phacelia
• Phacelia stebbinsii – Stebbins´ Phacelia
• Phacelia stellaris – star Phacelia, Brand´s Phacelia
• Phacelia tanacetifolia – lacy Phacelia
• Phacelia thermalis – heated Phacelia
• Phacelia vallicola – Mariposa Phacelia
• Phacelia vallis-mortae – Death Valley Phacelia
• Phacelia viscida – tacky Phacelia

Dermatitis: There are reports that glandular hairs of stems, flowers and leaves of some species of Phacelia secrete oil droplets that can cause an unpleasant skin rash (contact dermatitis) in some people, specifically from P. brachyloba, P. campanularia, P. crenulata, P. gina-glenneae, P. grandiflora, P. ixodes, P. minor, and P. pedicellata. The major contact allergen of P. crenulata has been identified as geranylhydroquinone and of P. minor as geranylgeranylhydroquinone.