Aesculus californica - California buckeye

California buckeye

The Bisexual California Buckeye – sinner or survivalist?
By Sue Ridgeway SCMG

A June 2012 article in the Huffington Post announced, in a bold, attention grabbing headline, “Ohio Man Demands State Revoke 'Bisexual' Buckeye's Status As State Tree.”  “Ohio's Jim Flechtner is demanding that the Aesculus glabra, better known as the Ohio Buckeye be revoked of state tree status because it bears male, female and bisexual flowers on the same tree.”

Fletchner, who originally submitted the letter to the editor of the “The Courier,” a newspaper in Northwestern Ohio, is said to be known for his satirical pieces.  So, we can only hope he was joking this time too. However, Mr. Fletcher is correct – the 13 to 19 species (and hybrids) of Aesculus, a widespread genus of the Hippocastanaceae (horse chestnut), a subfamily of Sapindaceae, are valued for their fragrant, showy, ornamental flowers – some of which are bisexual. Aesculus are distributed throughout Northern temperate climates – they are called common horse chestnuts in Europe, and buckeyes in North America. Their seeds, developing in round, fig, or pear shaped leathery capsules, are said to bear a striking resemblance, in color and shape, to the “eye of the buck.”

The only buckeye native to California is Aesculus californica, or California buckeye.  It is found growing below 4,000 feet throughout California and Southern Oregon.  It can grow as much as 10 inches a year, as either a large, multi-trunked shrub (found in Northern climes), or a small tree (30 plus feet high) in the Southern regions.

Aesculus californica is summer deciduous, sometimes defoliating in early July, and it is the first tree leafing out each year.  It grows during the wet winter and spring months when its neighbors are dormant, and enters dormancy in mid to late summer.  In cooler coastal climates, the leaves may last through mid-autumn.

Have you ever asked yourself: “What are those bright green trees with spectacular, erect clusters of white flowers” or, “it’s only July, what are all those dead and dying trees with pears on them?”

In almost poetic abandon – Glenn Keator, Ph.D., field botanist, and an author well know for conveying the awesome diversity and beauty of California's native plants, answers:

“Here is a fine plant for seasonal interest: silvery gray bark that’s shown to advantage from fall through winter; fanlike, palmately compound, apple-green leaves in spring and early summer; tight candles of white to palest pink, sweetly fragrant flowers in May or June; and curious, leathery, pear like seed pods with glossy brown seeds like chestnuts in fall.”

California buckeye is appreciated in the landscape as a native, water-wise, ornamental.  It can be planted to provide shade, pruned as a hedge, grown in containers, or used as a companion tree for color and contrast with live oaks; however, you don’t want to roast buckeye chestnuts on an open fire, at least, not if you intend to eat them. 

Aesculus californica nuts closely resemble the Christmas holiday icon, roasted sweet chestnuts (Castanea sativa - European sweet chestnut).  They are not the same; the fruits of horse chestnut and buckeye are unpleasant tasting and toxic.  Apparently, only ground squirrels find them palatable.

Although safe to handle, the large seeds contain glucoside aesculin – a toxic compound similar to those found in rat poisons.  Most cases of aesculin poisoning occur when people roast and eat the nuts.  Although rarely fatal, consuming large amounts of aesculin can result in “lack of coordination, twitching, restlessness, depression, vomiting, diarrhea, muscle weakness and occasionally paralysis and unconsciousness or worse.”
It’s not just the fruit that contains the toxins – the leaves and shoots are poisonous to livestock, and the flowers can also be very unpleasant – especially if you are an Asian/European honey bee.  

Aesculus californica, bearing a profusion of pollinator attracting, erect, white, fragrant inflorescences (flower spikes) up to eight inches long, is polygamo-monoecious; a tree with both unisexual and bisexual flowers on the same tree.  Because they have all four characteristics of a flower: sepals, petals, stamen and pistil, bisexual flowers are referred to as “complete” or “perfect” flowers.  

All the sweetly fragrant flowers of this tree provide a rich pollen and nectar source for native bees, hummingbirds and many species of butterflies, but apiaries of honey bees should never be placed near abundant stands of California buckeye. Even though the honey produced from buckeye is not poisonous to humans, Aesculus californica pollen  is hazardous to honey bees, none of which are native to California.  The term “buckeyed-bees” is used to describe bees that hatch with deformed, crippled wings or malformed legs and bodies.

California buckeye is a species superbly adapted for survival: with growth habits designed to circumvent the drought conditions of its habitat, with a highly effective reproductive strategy, with leaves and shoots protected from grazing animals by noxious, toxic compounds, with prolific flowers attracting multiple native pollinators, and with viable seeds too poisonous to be consumed.