Ceanothus

{{Short description|Genus of flowering plants}} {{Automatic taxobox |name=''Ceanothus'' |image=Ceanothus americanus.jpg |image_caption=''Ceanothus americanus'' flowers |taxon=Ceanothus |authority=L.<ref name="GRIN">{{cite web |url=http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?2210 |title=Genus: ''Ceanothus'' L. |work=Germplasm Resources Information Network |publisher=United States Department of Agriculture |date=2004-02-10 |access-date=2012-04-25 |archive-url=https://web.archive.org/web/20090114223302/http://www.ars-grin.gov/cgi-bin/npgs/html/genus.pl?2210 |archive-date=2009-01-14 |url-status=dead }}</ref> |subdivision_ranks=Species |subdivision=See text |synonyms = ''Forrestia'' Raf. |synonyms_ref = <ref name = powo/> }}

'''''Ceanothus''''' is a genus of about 50–60 species of nitrogen-fixing shrubs and small trees in the buckthorn family (Rhamnaceae).<ref name=EB1911>{{cite EB1911|wstitle=Ceanothus}}</ref><ref>{{Cite web |url=http://web.uconn.edu/mcbstaff/benson/Frankia/Rhamnaceae.htm |title=Untitled Document |access-date=2015-03-25 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304062125/http://web.uconn.edu/mcbstaff/benson/Frankia/Rhamnaceae.htm |url-status=dead }}</ref><ref name=powo/><ref name=cf/> Common names for members of this genus are '''buckbrush''', '''California lilac''', '''soap bush''', or just '''ceanothus'''.<ref name=usda/><ref name=waterwise/> The genus is native to North America,<ref name=powo/><ref name=bonapdiv/> ranging from Canada and the United States south through Mexico to Panama, with the center of diversity in the California floristic province of the western United States and Mexico, where around ~42 species are endemic out of the roughly ~58 species in the genus.<ref name="Burge"/><ref name="FnaCean"/> Most ''Ceanothus'' are shrubs, with some species rarely tree-like while others have a short mat-like habit. Species of ''Ceanothus'' can be evergreen or deciduous, may have thorns, and also have a diverse number of petal colors ranging from cream to deep blue to pink. Some reproduce strictly from seed, while others can resprout from their roots after a fire.<ref name="FnaCean"/><ref name="Jepson"/>

Valued as ornamental plants, prolific hybridization in ''Ceanothus'' makes them a popular source of horticultural cultivars, of which there are over 200 named selections. Ornamental ''Ceanothus'' hybrids have been cultivated since the 1830s, and a number of them have won the Royal Horticultural Society's Award of Garden Merit.

==Description== ''Ceanothus'' consists of shrubs that are rarely tree-like, twigs that are thorn-like or not, leaves that are persistent (evergreen) or deciduous in alternate or opposite arrangements (with the stems usually following the leaf arrangement), and generally have a venation on the underside of the leaves that is either pinnate or 3-veined from the base. The inflorescences may be terminal (emerging from the end of branches) or axillary, taking up umbel-like, raceme-like, and panicle-like aggregations of flower clusters. The flowers are bisexual, with 5 petals, and come in a variety of colors from white to cream, blue, purple, or rarely pink. The fruits are capsules, with a more or less spherical shape, generally divided into lobes of 3. Within the fruits are 3 small seeds.<ref name="FnaCean">{{cite journal |last1=Schmidt |first1=Clifford L. |last2=Wilken |first2=Dieter H. |title=Ceanothus |journal=Flora of North America |date=2016 |volume=12 |page=77 |url=https://floranorthamerica.org/Ceanothus |access-date=7 January 2026}}</ref><ref name="Jepson">{{cite web |last1=Burge |first1=Dylan O. |last2=Wilken |first2=Dieter H. |title=Ceanothus |url=https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=8834 |website=Jepson eFlora |publisher=Regents of the University of California |access-date=8 January 2026 |date=2020}}</ref>

Because of the difficulty in identifying ''Ceanothus'' due to the limited barriers in genetic exchange resulting in hybrids, and local and geographical variations within species, special attention must be given to identifying key characteristics of the species. The flower colors and mature fruits are important characters, but finding these characteristics can be challenging due to the short duration of flowering and the long maturation period of the fruits that follows. Other important characters include the life form, understanding the patterns of geographic distribution for the species, and the recognizing the soils preferred by different species.<ref name="FnaCean"/> ==Taxonomy== ''"Ceanothus"'' comes from {{langx|grc|κεάνωθος}} (''keánōthos''), which was applied by Theophrastus (371–287 BC) to a spiny<ref name="FnaCean"/> Old World plant, believed to be ''Cirsium arvense''.<ref>{{cite book |author=Elmore, Francis H. |title=Trees and Shrubs of the Southwest Uplands |publisher=Western National Parks Association |year=1976 |pages=195 |isbn=0-911408-41-X}}</ref><ref name="Austin">{{cite book |url=https://books.google.com/books?id=eS7lX_rC3GEC |first=Daniel F. |last=Austin |title=Florida Ethnobotany |publisher=CRC Press |year=2004 |isbn=978-0-8493-2332-4 |page=291}}</ref>

There are two subgenera within this genus: ''Ceanothus'' and ''Cerastes''. The former clade is less drought-resistant, having bigger leaves. The evolution of these two clades likely started with a divergence in the niches filled in local communities, rather than a divergence on the basis of geography.<ref name="AckerlySchwilk2006"/> The two clades are also sometimes recognized as sections, with the usage of section or subgenus being inconsistent in the literature on the genus. Subgenus ''Cerastes'' was not properly typified nor formally recognized until 2016. Despite the taxonomic difficulties, both clades are generally regarded as being deeply divergent and distinct based on phylogenetic research and morphological characteristics.<ref name="Burge">{{cite journal |last1=Burge |first1=Dylan O. |last2=Zhukovsky |first2=Katherine |last3=Wilken |first3=Dieter H. |title=A Taxonomic Conspectus of Ceanothus subgenus Cerastes (Rhamnaceae) |journal=Systematic Botany |date=1 January 2016 |volume=40 |issue=4 |pages=950–961 |doi=10.1600/036364415X689997 |url=http://www.bioone.org/doi/full/10.1600/036364415X689997 |access-date=6 January 2026 |language=en|url-access=subscription }}</ref>

The Californian species of ''Ceanothus'' are commonly known collectively as California lilacs, with individual species having more descriptive common names. Species native elsewhere have other common names such as New Jersey tea for ''C. americanus'', as its leaves were used as a black tea substitute during the American Revolution.<ref name=EB1911/><ref name=feis> {{cite web |url=http://www.fs.fed.us/database/feis/plants/shrub/ceaame/all.html |title=''Ceanothus americanus'' |author=Coladonato, Milo |year=1993 |work=Fire Effects Information System (online) |publisher=U.S.D.A; Forest Service |location=Rocky Mountain Research Station, Fire Sciences Laboratory (Producer) |access-date=March 3, 2016 }}</ref> In garden use, most are simply called by their scientific names or an adaptation of the scientific name, such as 'Maritime ceanothus' for ''C. maritimus''.

===Species=== The following species list is based on the treatments in the Flora of North America Volume 12 (2016) and ''A Taxonomic Conspectus of Ceanothus subgenus Cerastes (Rhamnaceae)'' by Burge et. al. (2016). Supplementary names are provided by Plants of the World Online and The Plant List.<ref name=powo/><ref name="PlantList">{{cite web | url = http://www.theplantlist.org/1.1/browse/A/Rhamnaceae/Ceanothus/ | title = The Plant List entry for ''Myrica'' | date = September 2013 | website = The Plant List, v.1.1 | publisher = Royal Botanic Gardens, Kew and the Missouri Botanical Garden | access-date = 15 December 2020}}</ref> ====Subgenus ''Ceanothus''==== {{Multiple image | total_width = 330 | image1 = 210403 039 Fallbrook - Ceanothus pendletonensis Camp Pendleton California Lilac.jpg | caption1 = ''Ceanothus pendletonensis'' with flowering inflorescences | image2 = Ceanothus thyrs. 008 php.jpg | caption2 = The fruits of ''Ceanothus thyrsiflorus'' | image3 = Ceanothus sanguineus 4839.JPG | caption3 = The leaves (underside) of ''Ceanothus sanguineus'' | perrow = 1/2 | header = ''Ceanothus'' subg. ''Ceanothus'' }} ''Ceanothus'' subgenus ''Ceanothus'' consists of evergreen or deciduous species with thin scale-like stipules, alternate leaves, branchlets that may be thorn-tipped, and inflorescences that are generally raceme-like to panicle-like, or occasionally umbel-like. The capsules lack horns, and are sometimes crested. Depending on the authority, there are about 21 to 32 species recognized in subgenus ''Ceanothus''. This subgenus is widely distributed across North America, from Canada, the United States and Mexico to Central America (Costa Rica, Guatemala, Panama). Many species in this subgenus have burls (root crowns) that can withstand wildfires, allowing them to respond to fire by resprouting.<ref name="Burge"/><ref name="FNASubgCean">{{cite journal |last1=Schmidt |first1=Clifford L. |last2=Wilken |first2=Dieter H. |title=Ceanothus subg. Ceanothus |journal=Flora of North America |date=2016 |volume=12 |page=79 |url=https://floranorthamerica.org/Ceanothus_subg._Ceanothus |access-date=7 January 2026}}</ref> {{div col|colwidth=350px}} * ''Ceanothus americanus'' L. – New Jersey tea; red root<ref>[http://wisplants.uwsp.edu/scripts/detail.asp?spcode=CEAAME University of Wisconsin–Stevens Point Plant Database: ''Ceanothus americanus''] {{webarchive|url=https://web.archive.org/web/20070116012715/http://wisplants.uwsp.edu/scripts/detail.asp?SpCode=CEAAME |date=2007-01-16 }}</ref> * ''Ceanothus arboreus'' Greene – feltleaf ceanothus * ''Ceanothus buxifolius'' Willd. ex Schult. & Schult.f. * ''Ceanothus caeruleus'' Lag * ''Ceanothus cordulatus'' Kellogg – whitethorn ceanothus * ''Ceanothus cyaneus'' Eastw. – San Diego buckbrush * ''Ceanothus dentatus'' Torr. & A.Gray – sandscrub ceanothus * ''Ceanothus depressus'' Benth. – junco * ''Ceanothus diversifolius'' Kellogg – pinemat * ''Ceanothus fendleri'' A.Gray – Fendler's ceanothus * ''Ceanothus fernandezii'' {{small|Villarreal, A.E.Estrada & Encina}}<ref>{{cite journal |last1=Villarreal-Quintanilla |first1=José A. |last2=Estrada-Castillón |first2=Eduardo |last3=Encina-Domínguez |first3=Juan A. |title=A new species of Ceanothus (Rhamnaceae) from Sierra Madre Occidental, Mexico |journal=Phytotaxa |date=5 September 2019 |volume=415 |issue=5 |pages=293–297 |doi=10.11646/phytotaxa.415.5.6}}</ref> * ''Ceanothus foliosus'' Parry – wavyleaf ceanothus ** subsp. ''foliosus'' Parry ** subsp. ''medius'' (McMinn) C.L.Schmidt ** subsp. ''vineatus'' (McMinn) C.L.Schmidt * ''Ceanothus griseus'' (Trel. ex B.L.Rob.) McMinn – Carmel ceanothus * ''Ceanothus hearstiorum'' Hoover & J.B.Roof – Hearst Ranch buckbrush * ''Ceanothus herbaceus'' Raf. – Jersey tea * ''Ceanothus impressus'' Trel. – Santa Barbara ceanothus * ''Ceanothus incanus'' Torr. & A.Gray – coast whitethorn * ''Ceanothus integerrimus'' Hook. & Arn. – deerbrush ceanothus * ''Ceanothus lemmonii'' Parry – Lemmon's ceanothus * ''Ceanothus leucodermis'' Greene – chaparral whitethorn * ''Ceanothus martini'' M.E.Jones – Martin's ceanothus * ''Ceanothus microphyllus'' Michx. – littleleaf buckbrush * ''Ceanothus ochraceus'' Suess. * ''Ceanothus oliganthus'' Nutt. – hairy ceanothus ** subsp. ''oliganthus'' Nutt. ** subsp. ''sorediatus'' (Hook. & Arn.) C.L.Schmidt * ''Ceanothus palmeri'' Trel. – Palmer ceanothus * ''Ceanothus papillosus'' Torr. & A.Gray – wartleaf ceanothus * ''Ceanothus parryi'' Trel. – Parry Ceanothus * ''Ceanothus parvifolius'' (S.Watson) Trel. – littleleaf ceanothus * ''Ceanothus pendletonensis'' D.O.Burge, Rebman, & M.R.Mulligan * ''Ceanothus sanguineus'' Pursh – redstem ceanothus * ''Ceanothus spinosus'' Nutt. – green bark ceanothus * ''Ceanothus thyrsiflorus'' Eschsch. – blueblossom * ''Ceanothus tomentosus'' Parry – woolyleaf ceanothus * ''Ceanothus velutinus'' Dougl. ex Hook. – snowbrush ceanothus ** subsp. ''laevigatus'' (Torr. & A.Gray) Piper & Beattie ** subsp. ''velutinus'' Dougl. ex Hook. {{div col end}}

====Subgenus ''Cerastes''==== {{Multiple image | total_width = 330 | image1 = Ceanothus cuneatus.jpg | image2 = Ceanothus megacarpus megacarpus 508146488.jpg | image3 = Ceanothus verrucosus 461538075.jpg | perrow = 1/2 | caption1 = ''Ceanothus cuneatus'' with flowering inflorescences | caption2 = The fruits of ''Ceanothus megacarpus'' | caption3 = The stem and leaves of ''Ceanothus verrucosus'' | header = ''Ceanothus'' subg. ''Cerastes'' }} ''Ceanothus'' subgenus ''Cerastes'' (S. Watson) Weberbauer consists of evergreen species with thick, wart-like stipules, branchlets that are not thorn-tipped, and leaves that are usually oppositely arranged (except in ''C. verrucosus'' and ''C. megacarpus'' var. ''megacarpus''). The leaves of plants in this subgenus are leathery in texture. The inflorescences are generally umbel-like, and rarely raceme-like. The capsules may be horned or not, and are usually not crested (except in ''C. divergens'' and ''C. gloriosus''). Depending on the authority, there are about 25 to 29 species recognized in subgenus ''Cerastes''. This subgenus is found in the mountainous western parts of the United States and Mexico, with most species restricted to California. Species in this subgenus strictly reproduce by seeds.<ref name="Burge"/><ref name="FNASubgCera">{{cite journal |last1=Schmidt |first1=Clifford L. |last2=Wilken |first2=Dieter H. |title=Ceanothus subg. Cerastes |journal=Flora of North America |date=2016 |volume=12 |page=94 |url=https://floranorthamerica.org/Ceanothus_subg._Cerastes |access-date=7 January 2026}}</ref> {{div col|colwidth=350px}} * ''Ceanothus arcuatus'' McMinn – arching ceanothus * ''Ceanothus bolensis'' S.Boyd & J.E.Keeley – Cerro Bola ceanothus * ''Ceanothus confusus'' J.T. Howell – Rincon Ridge ceanothus * ''Ceanothus × connivens'' Greene – trailing buckbrush * ''Ceanothus crassifolius'' Torr. – hoaryleaf ceanothus * ''Ceanothus cuneatus'' (Hook.) Nutt. – buckbrush ** subsp. ''cuneatus'' (Hook.) Nutt. ** subsp. ''fascicularis'' (McMinn) C.L.Schmidt ** subsp. ''rigidus'' (Nutt.) C.L.Schmidt ** subsp. ''sonomensis'' (Howell) C.L.Schmidt * ''Ceanothus decornutus'' V.T.Parker – Nicasio ceanothus * ''Ceanothus divergens'' Parry – Calistoga ceanothus * ''Ceanothus ferrisiae'' McMinn – coyote ceanothus * ''Ceanothus fresnensis'' Dudley ex Abrams – Fresno ceanothus * ''Ceanothus gloriosus'' J.T. Howell – Point Reyes ceanothus ** subsp. ''exaltatus'' (Howell) C.L.Schmidt ** subsp. ''gloriosus'' J.T. Howell ** subsp. ''masonii'' (McMinn) C.L.Schmidt ** subsp. ''porrectus'' (Howell) C.L.Schmidt * ''Ceanothus jepsonii'' Greene – Jepson ceanothus ** subsp. ''albiflorus'' (Howell) C.L.Schmidt ** subsp. ''jepsonii'' Greene * ''Ceanothus maritimus'' Hoover – maritime ceanothus * ''Ceanothus masonii'' McMinn – Mason's ceanothus * ''Ceanothus megacarpus'' Nutt. – bigpod ceanothus ** subsp. ''insularis'' (Eastw.) P.H.Raven ** subsp. ''megacarpus'' Nutt. * ''Ceanothus ophiochilus'' Boyd, Ross & Arnseth – Vail Lake ceanothus * ''Ceanothus otayensis'' H. E. McMinn – Otay Mountain buckbrush * ''Ceanothus pauciflorus'' Moc. & Sessé ex DC. – Mojave ceanothus * ''Ceanothus perplexans'' Trel. – cup-leaved ceanothus * ''Ceanothus pinetorum'' Coville – Coville ceanothus * ''Ceanothus prostratus'' Benth. – prostrate ceanothus ** subsp. ''confusus'' (Howell) C.L.Schmidt ** subsp. ''prostratus'' Benth. ** subsp. ''pumilus'' (Greene) C.L.Schmidt * ''Ceanothus pumilus'' Greene – dwarf ceanothus * ''Ceanothus purpureus'' Jepson – hollyleaf ceanothus ** subsp. ''divergens'' (Parry) C.L.Schmidt ** subsp. ''purpureus'' Jepson * ''Ceanothus roderickii'' Knight – Pine Hill buckbrush * ''Ceanothus sonomensis'' J.T. Howell – Sonoma ceanothus * ''Ceanothus verrucosus'' Nutt. – wart-stem ceanothus {{div col end}}

===Hybrids=== ''Ceanothus'' have few natural barriers to genetic exchange, as they share a common diploid chromosome number and lack strong isolating mechanisms,<ref name="FnaCean"/> resulting in a number of hybrids and integradation between species. Hybridization usually only occurs within subgenera, as crosses across subgenera produce sterile progeny. The role of hybridization creates difficulties in reliably circumscribing ''Ceanothus'' species, and many species were formerly recognized as hybrids, like ''Ceanothus otayensis'' and ''Ceanothus arcuatus''.<ref name="Burge"/> Some authorities do not recognize even named hybrids due to the difficulty of keying them out.<ref name="Jepson"/> There are at least 44 interspecific combinations reported in the literature.<ref name="FnaCean"/> The following hybrids have been described:<ref name="PlantList"/> {{div col|colwidth=350px}} * ''Ceanothus × lobbianus'' {{small|Hook.}} * ''Ceanothus × lorenzenii'' {{small|(Jeps.) McMinn}} * ''Ceanothus × mendocinensis'' {{small|McMinn}} * ''Ceanothus × rugosus'' {{small|Greene}} * ''Ceanothus × serrulatus'' {{small|McMinn}} * ''Ceanothus'' × ''vanrensselaeri'' Roof * ''Ceanothus × veitchianus'' {{small|Hook.}} {{div col end}}

The status of the following hybrids is unresolved:<ref name="Burge"/><ref name="PlantList"/> {{div col|colwidth=350px}} * ''Ceanothus'' × ''arnoldii'' Dippel * ''Ceanothus × bakeri'' Greene ex McMinn * ''Ceanothus'' × ''burkwoodii'' auct. * ''Ceanothus'' × ''burtonensis'' Renss. * ''Ceanothus'' × ''cyam'' L.W.Lenz * ''Ceanothus'' × ''delilianus'' Spach * ''Ceanothus'' × ''flexilis'' McMinn * ''Ceanothus × humboldtensis'' {{small|Roof}} * ''Ceanothus'' × ''intermedius'' Koehne * ''Ceanothus'' × ''pallidus'' Koehne * ''Ceanothus'' × ''pallidus'' Lindl. * ''Ceanothus'' × ''roseus'' Koehne {{div col end}}

==Distribution== thumb|right|''Ceanothus americanus'' (fruit left, flowers right) Plants in this genus are widely distributed and can be found on dry, sunny hillsides from coastal scrub lands to open forest clearings, from near sea level to {{convert|9000|ft|m}} in elevation. These plants are profusely distributed throughout the Rocky Mountains from British Columbia south through Colorado, the Cascades of Oregon and California, and the Coastal Ranges of California.

''Ceanothus velutinus'' is perhaps the most widespread member of this genus, occurring through much of western North America.<ref name=Tilford>Edible and Medicinal Plants of the West, Gregory L. Tilford, {{ISBN|0-87842-359-1}}</ref> The plants in this genus often co-occur with one another, especially when they are more distantly related.<ref name="AckerlySchwilk2006">{{cite journal|last1=Ackerly|first1=D. D.|last2=Schwilk|first2=D. W.|last3=Webb|first3=C. O.|title=Niche evolution and adaptive radiation: Testing the order of trait divergence|journal=Ecology|volume=87|issue=sp7|year=2006|pages=S50–S61|issn=0012-9658|doi=10.1890/0012-9658(2006)87[50:NEAART]2.0.CO;2|pmid=16922302}}</ref>

==Uses== [[File:Ceanothus integerrimus 01.jpg|thumb|''Ceanothus integerrimus'' (deerbrush) in Yosemite National Park]]

===Wildlife=== Ceanothus is a good source of nutrition for deer, specifically mule deer along the West Coast of the United States. However, the leaves are not as nutritious from late spring to early fall as they are in early spring. Porcupines and quail have also been seen eating stems and seeds of these shrubs. The leaves are a good source of protein and the stems and leaves have been found to contain a high amount of calcium.

===Cultivation=== Many ''Ceanothus'' species are popular ornamental plants for gardens. The ease of hybridization in ''Ceanothus'' makes them attractive plants for horticultural cultivars. One of the first and most popular cultivars was 'Gloire de Versailles' (''Ceanothus'' × ''delilianus''), a cross of the eastern North American species ''C. americanus'' and the Mexican species ''C. caeruleus'', which was created in France in the 1830s. There are over 200 named selections of ''Ceanothus''.<ref name="FnaCean"/><ref name="glovers"/>

=== Royal Horticultural Society's Award of Garden Merit cultivars=== The following cultivars and hybrids have gained the Royal Horticultural Society's Award of Garden Merit ({{as of|2017|lc=y}}):<ref>{{cite web |url=https://www.rhs.org.uk/plants/pdfs/agm-lists/agm-ornamentals.pdf |title=AGM Plants - Ornamental |date=July 2017 |page=16 |publisher=Royal Horticultural Society |access-date=24 January 2018}}</ref> {{div col|colwidth=15em}} *’Autumnal Blue’<ref>{{cite web |url=https://www.rhs.org.uk/Plants/91791/i-Ceanothus-i-Autumnal-Blue/Details |title=RHS Plantfinder - ''Ceanothus'' 'Autumnal Blue' |publisher=Royal Horticultural Society |access-date=21 January 2018}}</ref> *'Blue Mound'<ref>{{cite web|title=RHS Plant Selector - ''Ceanothus'' 'Blue Mound'|url=https://www.rhs.org.uk/Plants/63246/Ceanothus-Blue-Mound/Details | access-date=15 April 2020}}</ref> *'Burkwoodii'<ref>{{cite web|title=RHS Plant Selector - ''Ceanothus'' 'Burkwoodii'|url=https://www.rhs.org.uk/Plants/96855/Ceanothus-Burkwoodii/Details | access-date=15 April 2020}}</ref> *'Cascade'<ref>{{cite web|title=RHS Plant Selector - ''Ceanothus'' 'Cascade'|url=https://www.rhs.org.uk/Plants/91792/Ceanothus-Cascade/Details | access-date=15 April 2020}}</ref> *'Concha'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/97563/Ceanothus-Concha/Details | title = ''Ceanothus'' 'Concha' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Dark Star'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/95793/Ceanothus-Dark-Star/Details | title = ''Ceanothus'' 'Dark Star' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Gloire de Versailles'<ref name="glovers">{{cite web | url = https://www.rhs.org.uk/Plants/69338/Ceanothus-x-delileanus-Gloire-de-Versailles/Details | title = Ceanothus × ''delileanus'' 'Gloire de Versailles' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Mystery Blue'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/274981/Ceanothus-thyrsiflorus-Mystery-Blue/Details | title = ''Ceanothus thyrsifolius'' 'Mystery Blue' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Perle Rose'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/52985/Ceanothus-x-pallidus-Perle-Rose/Details | title = ''Ceanothus'' × ''pallidus'' 'Perle Rose' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Puget Blue'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/95971/Ceanothus-Puget-Blue/Details | title = ''Ceanothus'' 'Puget Blue' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Skylark'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/236885/Ceanothus-Skylark/Details | title = ''Ceanothus'' 'Skylark' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Topaze'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/46202/Ceanothus-x-delileanus-Topaze/Details | title = ''Ceanothus'' × ''delineanus'' 'Topaze' | publisher = RHS | access-date = 12 April 2020}}</ref> *'Trewithen Blue'<ref>{{cite web | url = https://www.rhs.org.uk/Plants/3253/Ceanothus-arboreus-Trewithen-Blue/Details | title = ''Ceanothus arboreus'' 'Trewithen Blue' | publisher = RHS | access-date = 12 April 2020}}</ref> *''C. thyrsifolius'' var. ''repens'' <ref>{{cite web | url = https://www.rhs.org.uk/Plants/94754/Ceanothus-thyrsiflorus-var-repens/Details | title = ''Ceanothus thyrsifolius'' var. ''repens'' | publisher = RHS | access-date = 12 April 2020}}</ref> {{div col end}}

Other cultivars available include:- {{div col|colwidth=22em}} *'Anchor Bay' <ref>[http://www.smgrowers.com/products/plants/plantdisplay.asp?strSearchText=Ceanothus&plant_id=1755&page=San Marcos Growers Horticulture Database: ''Ceanothus'' 'Anchor Bay']</ref> *'Diamond Heights' (variegated leaves)<ref>[http://www.smgrowers.com/products/plants/plantdisplay.asp?plant_id=2992 San Marcos Growers Horticulture Database: ''Ceanothus griseus horizontalis'' 'Diamond Heights']</ref> *'Ray Hartman'<ref>[http://www.smgrowers.com/products/plants/plantdisplay.asp?strSearchText=Ceanothus&plant_id=372&page=San Marcos Growers Horticulture Database: ''Ceanothus'' 'Ray Hartman']</ref> *'Snow Flurry'<ref>[http://www.smgrowers.com/products/plants/plantdisplay.asp?strSearchText=Ceanothus&plant_id=373&page= San Marcos Growers Horticulture Database: ''Ceanothus thyrsiflorus'' 'Snow Flurry']</ref> {{div col end}}

There are also more cultivars and hybrids of ''Ceanothus arboreus'', ''Ceanothus griseus horizontalis'' (groundcovers), and ''Ceanothus thyrsiflorus'' in the nursery trade.

====Propagation==== Propagation of ceanothus is by seed, following scarification and stratification. Seeds are soaked in water for 12 hours followed by chilling at 1 °C for one to three months. It can also sprout from roots and/or stems. Seeds are stored in plant litter in large quantities. It is estimated that there are about two million seeds per acre in forest habitats. Seeds are dispersed propulsively from capsules and, it has been estimated, can remain viable for hundreds of years. In habitat, the seeds of plants in this genus germinate only in response to range fires and forest fires. {{Citation needed|date=December 2013}}

===Other uses=== Native Americans used the dried leaves of this plant as an herbal tea, and early pioneers used the plant as a substitute for black tea. Miwok Indians of California make baskets from Ceanothus branches. ''Ceanothus integerrimus'' has been used by North American tribes to ease childbirth.<ref>Moerman, D. (1988). ''Native American Ethnobotany''. Timber Press, Oregon.</ref>

== Nitrogen fixation == ''Ceanothus'' is actinorhizal, meaning it fixes nitrogen through a symbiotic relationship with ''Frankia.'' Six genera within Rhamnaceae are actinorhizal, but ''Ceanothus'' is the only genus not in the monophyletic tribe Colletieae. This suggests that actinorhizal symbiosis may have evolved twice in Rhamnaceae.<ref>{{Cite web|last=Vining|first=Susan|date=2020-02-26|title=Rhamnaceae {{!}} Frankia|url=https://frankia.mcb.uconn.edu/home/rhamnaceae/|access-date=2021-06-12|language=en-US}}</ref> ''Frankia'' forms nodules on the roots of ''Ceanothus'', converting atmospheric nitrogen ({{chem|N|2}}) into ammonia ({{chem|NH|3}}) using nitrogenase.<ref>{{Cite web|last=Vining|first=Susan|date=2020-02-26|title=Nodules {{!}} Frankia|url=https://frankia.mcb.uconn.edu/home/nolules/|access-date=2021-06-12|language=en-US}}</ref><ref>{{Cite web|last=Vining|first=Susan|date=2020-02-26|title=Nitrogen Fixation {{!}} Frankia|url=https://frankia.mcb.uconn.edu/frankia-biology/nitrogen-fixation/|access-date=2021-06-12|language=en-US}}</ref>

==References== {{Reflist|refs= <ref name=bonapdiv>{{cite web |title=Largest Genera in Continental North America |url=http://bonap.org/2015_SpecialtyMaps/Most%20Number%20of%20Native%20Species/Native%20Species%20per%20Genus.html |website=BONAP |access-date=29 September 2019}}</ref> <ref name=cf>[http://www.calflora.org/cgi-bin/specieslist.cgi?where-genus=Ceanothus Calflora Database: Index of ''Ceanothus'' species native to California]</ref> <ref name=powo>{{cite web |title=''Ceanothus'' L. |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:30006383-2 |website=Plants of the World Online |publisher=Royal Botanical Gardens Kew |access-date=2 December 2023}}</ref> <ref name=usda>{{PLANTS |id=CEANO |taxon=Ceanothus |access-date=29 September 2019}}</ref> <ref name=waterwise>McMahan, L. R. [https://extension.oregonstate.edu/sites/default/files/documents/1/waterwise-plant-profiles.pdf WaterWise Plant Profiles]. Oregon State University Extension Service.</ref> }}

Category:Ceanothus Category:Rhamnaceae genera Category:Flora of Northern America Category:Botanical taxa named by Carl Linnaeus Category:Garden plants of North America Category:Drought-tolerant plants Category:Saponaceous plants Category:Flora of California