Species
+

Ceanothus thyrsiflorus Eschw.

Blue Blossom Ceanothus, Blueblossom, California-lilac, blueblossom

Climate known 68 photographs
Add one to my plants Sow seed

Every figure on this page is derived from public data by a stated rule and says its source; nothing here is written by a person or a model, except the Wikipedia passage, which is quoted and marked as such. How it is made.

Summary

Ceanothus thyrsiflorus, known as blueblossom or blue blossom ceanothus, is an evergreen shrub in the buckthorn family Rhamnaceae that is endemic to Oregon and California in the US. The terms 'Californian lilac' and 'Mountain lilac' are also applied to this and other varieties of ceanothus, though it is not closely related to Syringa, the true lilac.

Text from Wikipedia, “Ceanothus thyrsiflorus”, CC BY-SA 4.0, quoted as written. Kept separate from everything derived here.

About the genus · Ceanothus

Ceanothus is a genus of about 50–60 species of nitrogen-fixing shrubs and small trees in the buckthorn family (Rhamnaceae). Common names for members of this genus are buckbrush, California lilac, soap bush, or just ceanothus. The genus is native to North America, 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. More on Wikipedia ›

The opening of Wikipedia, “Ceanothus”, CC BY-SA 4.0, quoted as written.

Family
Rhamnaceae
Described by
Eschw.
Native to
Oregon, California, Mexico Northwest
Wild records
1442 in range· 339 open

At a glance

Warmest month
21°C
Aug, mean day; nights 13 °C (CHELSA)
Rain
917mm/yr
8 wet months · peak Jan 180 mm (CHELSA)
Light
14–50DLI
mol/m²/day, winter to summer, open sky (CHELSA shortwave)
In short condensed by rule from the cultivation cards · not written by a person
Rain rule: a winter growing season, December to March in the northern hemisphere (December to March at the habitat, northern). Habitat rain 917 mm a year, wettest January at 180 mm, driest July at 1 mm (habitat calendar, northern hemisphere). Open sky over the habitat: 14 to 50 mol/m²/day. Cold floor 2.8 °C (1st-percentile habitat night, NASA POWER).
Each sentence is one card's own one-line form, written by the same rule as the card (Its year, Rain, Light, Temperature); the note cannot say what a card does not. Months are given for the northern hemisphere (set your site in Settings to change this), and the habitat's own alongside. The cards · the figures.

Also known as Ceanothus elegans Lem.; Ceanothus thyrsiflorus var. chandleri Jeps.; Ceanothus thyrsiflorus var. repens Mc Minn; Forrestia thyrsoides Raf.

Cultivation

Its year Rain rule: a winter growing season, December to March in the northern hemisphere (December to March at the habitat, northern).

This species’ habitat figures, and what two fixed rules read from them.

The rain rule reads a winter growing season: 70% of the year's rain (653 mm of 917 mm) falls in December to March, cooler than the year (wet-season mean 10.2 °C against a yearly mean of 13.0 °C). Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: June to September.

Read from the median year of CHELSA monthly rainfall and mean temperature across the envelope cells: the rain rule takes the smallest set of months carrying 70% of the rain and calls it winter when its mean is more than half a degree below the year's, summer when more than that above, and neither in between; the temperature rule, used only under 120 mm, names the cooler six months when they are at least a degree cooler than the other six. Months are shifted for the other hemisphere only where the temperature curve gives a season to reverse. A reading of the curves, not an observation of the plant.

Rain Habitat rain 917 mm a year, wettest January at 180 mm, driest July at 1 mm (habitat calendar, northern hemisphere).

This species’ habitat figures, with their source.

917 mm a year at the habitat, 653 mm of it December to March. Wettest month January at 180 mm, driest July at 1 mm; 2 months under 5 mm. Across the envelope cells the year's total runs 521 mm to 1974 mm (10th to 90th percentile of each cell's own year) (median year across the envelope cells, CHELSA; habitat calendar, northern hemisphere).

CHELSA monthly precipitation, median year across the envelope cells. The rain that falls where the species is recorded; nothing about how the plant takes water.

Light Open sky over the habitat: 14 to 50 mol/m²/day.

This species’ habitat figures, with their source.

Open sky over the habitat: 14 to 50 mol/m²/day across the year (daily light integral, median year across the envelope cells, CHELSA; the lowest 10th-percentile month across the cells is 9, the highest 90th-percentile month 52).

CHELSA shortwave radiation at each envelope cell, a daily-mean flux taken to a daily total and converted at 2.07 mol of PAR per MJ. The sky over the habitat, measured; what reaches a plant under a rock, a shrub or a shade cloth is not.

Warmth and air Cold floor 2.8 °C (1st-percentile habitat night, NASA POWER).

This species’ habitat figures, with their source.

Temperature

Coldest: the 1st-percentile night over 44 years at the typical cell is 2.8 °C, the absolute minimum -7.5 °C, 25 frost nights in 44 years (NASA POWER daily minima). Warmest: the 99th-percentile day is 26.8 °C. Monthly means: coldest night 6.8 °C in January (across the envelope cells 4.0 °C to 9.0 °C), warmest day 21.1 °C in August (median year across the envelope cells, CHELSA). Cold floor: 2.8 °C, which is the 1st-percentile night over 44 years at the typical cell (NASA POWER).

NASA POWER daily minima and maxima 1981–2024 at the typical cell, lapse-corrected to its elevation; CHELSA monthly means, median year across the envelope cells, CHELSA. The cold floor is the figure named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity

Relative humidity at the habitat: 61 to 64% across the year (monthly means, median year across the envelope cells, CHELSA). A figure about the air, saying nothing about how the plant takes water.

CHELSA relative humidity, median year across the envelope cells.

The figures the cards read from are in Climate below, and where they came from in Natural habitat.

Climate across the habitat

Habitat climate through the yearMean day from 13 °C in Dec to 21 °C in Aug; mean night from 7 °C in Jan to 13 °C in Aug. The cold quarter, Dec to Feb, is the three months around the coldest night. 917 mm of rain a year, most in Jan. The bands show the 10th to 90th percentile across 342 habitat cells. Over 44 years at the typical cell the absolute minimum was -7.5 °C and the 99th-percentile day 26.8 °C; neither is dated to a month. Beneath: daily light integral and relative humidity through the year, each on its own scale.-10°10°20°30°frost26.8° 99th-percentile day (undated)-7.5° lowest night in 44 yrs (undated)°C · day and nightcold quarter0100200300400500mm rainDLI 14–50RH 61–64 %JanFebMarAprMayJunJulAugSepOctNovDec
day night rain 10th–90th percentile across 342 habitat cells cold quarter: the three months around the coldest night extremes over 44 years at the typical cell, marked at the edge: undated DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C13 / 11–1513 / 11–1614 / 12–1715 / 13–1817 / 14–2119 / 15–2421 / 16–2721 / 17–2621 / 17–2519 / 16–2215 / 13–1813 / 11–15
Night °C7 / 4–97 / 4–98 / 5–109 / 6–1010 / 9–1112 / 10–1313 / 12–1513 / 12–1513 / 12–1512 / 10–139 / 7–117 / 4–9
Rain mm180 / 105–338166 / 101–277131 / 83–24858 / 37–14925 / 12–877 / 3–521 / 1–113 / 1–167 / 5–3946 / 25–126117 / 57–295176 / 86–404
DLI15 / 11–1921 / 17–2530 / 25–3440 / 35–4346 / 43–5050 / 47–5250 / 48–5245 / 43–4737 / 34–4027 / 23–3018 / 13–2114 / 9–17
RH %62 / 57–6663 / 59–6564 / 60–6663 / 57–6563 / 57–6762 / 56–6763 / 54–6963 / 54–7062 / 54–6861 / 54–6662 / 56–6661 / 57–65

Each figure is the median across the 342 grid cells holding the 1391 in-range records, with the 10th–90th percentile span across those cells after the slash where it differs. Extremes and elevation were read at the typical cell 945:1110 (42.725, -124.475). Over 44 years there: absolute minimum -7.5 °C, 1st-percentile night 2.8 °C, 99th-percentile day 26.8 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Envelope: median and 10th–90th percentile of each month across the 342 distinct grid cells holding the 1391 in-range records; extremes and elevation at the typical cell 945:1110 (its coldest month's mean night nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 42.50_-124.375, lapse-corrected -244 m at 6.5 °C/km. Elevation: ETOPO 2022, 52 m (cell mean).

Natural habitat

Native range as published by WCVP; the marker is where the records are densest and decides nothing: the climate was read across every in-range record's cell, not at the marker.
Openly licensed records inside the range, framed on where they fall.
NativeOregon, California, Mexico Northwest
Kew's description“shrub or tree” · “temperate”· quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Map marker37.599, -122.424 · in the densest population, 1195 records (83% of those in range)
Evidence usedThe map marker and the climate envelope rest on all 1442 georeferenced records inside the native range; the map shows only the 339 openly licensed ones, which alone would put the marker in the same place. 13 records outside the range (gardens, roadsides, misidentifications) ignored. 51 in-range records are placed to worse than 10 km and stay on the map but off the climate.
The map markerthe map marker: the openly licensed record nearest the middle of the densest 1° population of the 1442 in-range records; it decides nothing.

Photographs

Ceanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorusCeanothus thyrsiflorus

Photographs: (c) Henrik Kibak, some rights reserved (CC BY) (7); (c) joergmlpts, some rights reserved (CC BY).

Photographs: iNaturalist and Wikimedia Commons did not answer when this page was built; what is shown came from the sources that did.

Papers naming this species

Works whose title or abstract names Ceanothus thyrsiflorus, most cited first, from OpenAlex (CC0). A mention, not a cultivation source: nothing on this page is drawn from them.

Control of Phytophthora species in plant stock for habitat restoration through best management practices
Laura Sims, Steven A. Tjosvold, D. L. Chambers, Matteo Garbelotto (2018) · Plant Pathology
Colletotrichum spp. causing anthracnose on ornamental plants in northern Italy
Vladimiro Guarnaccia, Ilaria Martino, G. Gilardi, Angelo Garibaldi (2020) · Journal of Plant Pathology
Modelling the effects of plant species on biocontrol effectiveness in ornamental nursery crops
David J. Skirvin, Michael Williams, J. S. Fenlon, K. D. Sunderland (2002) · Journal of Applied Ecology
Landscape-Scale Vegetation Change Following Fire in Point Reyes, California, USA
Alison B. Forrestel, Max A. Moritz, Scott L. Stephens (2011) · Fire Ecology
Comparative Analysis of the Nodule Transcriptomes of Ceanothus thyrsiflorus (Rhamnaceae, Rosales) and Datisca glomerata (Datiscaceae, Cucurbitales)
Marco Salgado, Robin van Velzen, Thanh Van Nguyen, Kai Battenberg (2018) · Frontiers in Plant Science
Phylogenetic placement of unculturedCeanothusmicrosymbionts using 16S rRNA gene sequences
Nancy J. Ritchie, David D. Myrold (1999) · Canadian Journal of Botany
First Record of Crown and Root Rot Caused by Cylindrocladium pauciramosum on California Lilac in Italy
G. Polizzi, A. Vitale, Dalia Aiello, G. Parlavecchio (2006) · Plant Disease
Green roof irrigation management based on substrate water potential assures water saving without affecting plant physiological performance
Martina Tomasella, Enrico De Nardi, Francesco Petruzzellis, Sergio Andri (2022) · Ecohydrology

Similar habitat climate the 6 species whose habitat climate is nearest this one's: mean day and night, month by month, and rain on a log scale, in calendar order, so a habitat with the same seasons six months out is far, not near. Nothing else counts: not range, not family.

Other Ceanothus 3 in the reference

History & registers

Where this page came from built 2026-09-20 · dossier v2 · node
gbif.species answeredcarried from build of 2026-09-20 (offline re-derivation; the backbone was not asked)
gbif.synonyms answeredcarried from build of 2026-09-20 (offline re-derivation; the backbone was not asked)
gbif.vernacular answeredcarried from build of 2026-09-20 (offline re-derivation; the backbone was not asked)
wcvp.distribution answered
gbif.occurrences answeredGBIF occurrence download https://doi.org/10.15468/dl.3h4zam
climate answered
wikidata answeredcarried from build of 2026-09-20 (rederive); that build: carried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
wikipedia answeredcarried from build of 2026-09-20; this build: skipped
inat.taxon not askedcarried from build of 2026-09-20 (rederive)
inat.photos.wild answeredcarried from build of 2026-09-20; this build: skipped
inat.photos.cultivated nothing to reportcarried from build of 2026-09-20 (rederive); that build: carried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
commons not askedcarried from build of 2026-09-20 (rederive); that build: carried from build of 2026-09-19 (rederive); that build: carried from build of 2026-09-19 (rederive)
gbif.media answered
openalex answeredcarried from build of 2026-09-20; this build: skipped

Every upstream is recorded as having answered, reported nothing, or refused. Only “nothing to report” is ever shown as an absence. Records came from 51 datasets via GBIF.org; each carries its own licence.