The California buckeye, Aesculus californica, begins to bloom in April or May, depending on location and on the duration of the winter rains. The tree is perhaps about ten to twelve feet tall when it grows in the full sun of chaparral. Chaparral is a plant community adapted to the summer-dry, winter-wet Mediterranean climate of Coastal Range California. In moister areas, such as the canyons and ravines of the Coast Range, the California buckeye may grow larger, perhaps reaching a height of 25 feet. The tree has a rounded crown and a spreading habit.
The inflorescences of the California buckeye range from white to pink in color. Some people say they smell good, but some say their smell is unpleasant. In any case, they are composed of many florets each with long stamens that hang out of the flower, and arranged in a spike about five or six inches long. The leaves of the buckeye tree are palmate, long serrate ovals of dark green above and a paler green below. The juvenile foliage is often downy, especially on the underside, but becomes smoother with maturity.
The flowers, fruit, and seeds of the California buckeye are poisonous. Various tribes of Native Americans, whom the Spanish called collectively Costanoans (which may be translated as “coastal dwellers”), exploited this attribute when they placed the seeds in pools of water to stun fish, which they then gathered, cooked, and ate. When some “Costanoan” tribes could not find other food, they reportedly leached the poison out of the seeds with repeated soaking and boiling, and then cooked and ate them.
Because of the poison, the USDA (see footnote) suggests that honeybees not be allowed to gather nectar from California buckeye trees. Deer do eat the young shoots, without apparent harm, and squirrels do gather and store the ripe seeds, which resemble chestnuts in appearance. The California buckeye is a member of the horse-chestnut family.
Because it essentially does not rain at all in California in the summer, the ground dries out. At some point in the summertime, the dryness of the soil reaches a point that signals the California buckeye to begin shedding its leaves. This is obviously an adaptation to the particular climate, like the thick waxy moisture-retaining leaves of many other members of the chaparral plant community. The California buckeye becomes leafless months sooner than other local deciduous florae, with the precise timing of its leaf fall dependent upon weather. The gray-barked tree often appears to be dead to people unfamiliar with local conditions, until sufficient winter moisture causes it to leaf out again in late fall or early winter.