Aesculus is the genus for both Buckeye and Horsechestnut. There are six species commonly found in the landscape. One of the best ways to distinguish between species is by their flowers and four of them are in bloom. The term buckeye is used for those Aesculus native to North America. They include Ohio buckeye, Aesculus glabra, a medium size tree 30-50' in height. It is the first Aesculus species to bloom in spring.
The flowers are greenish white and the stamens and pistils extend beyond the petals.
The fruits of Ohio buckeye are spiny when young and warty or prickly when mature. The petioles of Ohio buckeye are usually green and the leaves, made up of five leaflets, are 6" across and are stiff.
Yellow buckeye, Aesculus flava is a large tree 50-90' in height. It also has large leaves 12"-15" across and the leaflets are often pendulous.
The flowers are a light yellow with a blotch that changes from gold to orange to red and the flower ages. A key identification feature is the stamens and pistils are contained within the petals.
Red buckeye, Aesculus pavia. is a small tree typically less than 25’ in height.
The panicles of red buckeye are less dense than either Ohio or yellow buckeye; the flower petals can range in color from bright red to yellow with reddish overtones. These flowers are very attractive to hummingbird.
Note the red color of the petioles of red buckeye; the leaves are stiff and approximately 6" across.
There are many natural hybrids between Ohio, yellow and red buckeyes in all possible combinations. One of the best known is Autumn Splendor Buckeye, Aesculus x arnoldiana 'Autumn Splendor'.
This plant was selected for its glossy green foliage that is more resistant to both leaf scorch (an abiotic issue) and leaf blotch caused by Guignardia aesculi and for its good fall color. The flowers of Autumn Splendor buckeye are very similar to Ohio buckeye.
Bottlebrush Buckeye, Aesculus parviflora is a summer blooming large shrub that can reach up to 10' in height. Currently, the panicles with immature flower buds are visible, and we can expect to see flowers in July.
Bottlebush buckeye flowers are attractive to swallowtail butterflies, hummingbirds and a variety of other pollinators.
Horsechestnut is the term used for Aesculus from Europe or Asia. The most popular is Aesculus hippocastanum, common horsechestnut.
These get to be large trees 50-75’ in height. They can be quite spectacular in bloom as nearly every branch is tipped with a 12" panicle of creamy white flowers with a distinctive blotch that changes from yellow to a purplish red color as the flower ages.
The leaves of common horsechestnut are similar in size to those of yellow buckeye but they are stiff and usually have seven obovate leaflets.
There is also a double flowering cultivar, Double White Horsechestnut, Aesculus hippocastanum ‘Baumannii’.
The other striking Aesculus is a hybrid between the common horsechestnut and red buckeye. Aesculus x carnea also know as the red horsechestnut. This is a medium sized tree 30-50'.
There are three popular cultivars: Ruby Red Flowered Horsechestnut, Aesculus x carnea ‘Briotii',
Fort McNair Horsechestnut Aesculus x carnea ‘Fort McNair’
and O’Neill Red Horsechestnut Aesculus x carnea ‘O’Neill’.
All have bell shaped flowers that open pink and gradually darken rose. The leaflets of Aesculus x carnea often have a crinkled appearance.
Unfortunately, both common horsechestnut and red horsechestnut are both highly susceptible to Guignardia aesculi the organism that causes leaf blotch which can limit their effectiveness in the landscape.
Flowering can really help with the identification process.
One final note. If you purchase a buckeye or horsechestnut, SAVE THE TAG!