It is a large shrub or small tree growing to 4–12 m tall, with gray bark often coated with lichens or mosses. It typically is multi-trunked with a crown as broad as it is high. The leaves are dark green, palmately compound with five (rarely seven) leaflets, each leaflet 6–17 cm long, with a finely toothed margin and (particularly in spring) downy surfaces. The leaves are tender and prone to damage from both spring freezing or snow and summer heat and desiccation.
The flowers are sweet-scented, white to pale pink, produced in erect panicles 15–20 cm long and 5–8 cm broad. The fruit is a fig-shaped capsule 5–8 cm long, containing a large (2–5 cm), round, orange-brown seed; the seeds are poisonous. The California Buckeye has adapted to its native Mediterranean climate by growing during the wet winter and spring months and entering dormancy in late summer, though those growing in coastal regions tend to hold on to their leaves until mid-autumn; it begins the year's growth in early spring and begins dropping leaves by mid-summer.
Distribution and habitat 
This buckeye is found growing in a wide range of conditions from crowded, moist, semi-shaded canyon bottoms to dry south-facing slopes and hilltops. It is also widely distributed in the state, growing along the central coast, in the foothills and lower elevations of the Sierra Nevada, in the foothills of the Siskiyou Mountains in the Rogue Valley in Oregon. In northern California up to 1700 m altitude and in the Cascade range.
In the coastal ranges north of Big Sur it is found growing alone on slopes or intermingled with Valley Oak, Oregon Oak, Coast Live Oak and California Bay Laurel. In the foothills of the Sierra Nevada it can be found standing alone in grassland at the lowest elevations, intermingled in Blue Oak woodlands at intermediate elevations, and in mixed evergreen forests of Black oak, Digger Pine, Ponderosa Pine and Interior Live Oak as it nears the limit of its range.
Local native American tribes, including the Pomo, Yokut, and Luiseño, used the poisonous nuts to stupefy schools of fish in small streams to make them easier to catch. The bark, leaves, and fruits contain the neurotoxic glycoside aesculin, which causes hemolysis of red blood cells. Buckeye also makes a good fireboard for bowdrill or hand drill.
Native groups occasionally used the nuts as a food supply when the acorn supply was sparse; after boiling and leaching the toxin out of the nut meats for several days, they could be ground into a meal similar to that made from acorns. The nectar of the flowers is toxic to the Asian/European honeybee, so the trees should not be planted near apiaries. When the shoots are small and leaves are new, they are lower in toxins and are grazed by livestock and wildlife. The flowers are a rich nectar source for many species of butterflies.
It is used as an ornamental plant for its striking leaf buds, lime green foliage, fragrant white flowers, red-brown foliage in early summer, and architectural silver branches through fall. Trees are long lived estimated between 250-280 (300 maximum)years.
The tree acts as a soil binder, which prevents erosion in hilly regions.
- Elna S. Bakker (1984). An island called California: an ecological introduction to its natural communities. University of California Press. p. 74. ISBN 978-0-520-04948-2. Retrieved 2011-06-11.
- Philip Alexander Munz, David D. Keck (1973). A California Flora. University of California Press. p. 994. ISBN 978-0-520-02405-2. Retrieved 2011-06-20.
- Kat Anderson, Wayne Roderick. California Buckeye, in the USDA NRCS Plant Guide (Report). USDA. http://plants.usda.gov/plantguide/pdf/cs_aeca.pdf. Retrieved 2011-06-20.
- Howard, Janet L.. Aesculus californica, in the USDA Forest Service Fire Effects Information System (Report). USDA Rocky Mountain Research Station, Fire Sciences Laboratory. http://www.fs.fed.us/database/feis/plants/tree/aescal/all.html. Retrieved 2011-11-07.
- Kevin Hintsa. Watching Butterflies on Mount Diablo (Report). http://www.mdia.org/Wildlife/wbutterfly.htm. Retrieved 2011-11-07.