When is a Chestnut not... By Andrew Fowler 2/4/02

Last year I was at the Rochester Public Market peddling my plants, a collection of oddball stuff and other more mainstream offerings. I had these small trees/shrubs with large palmate leaves and tall candle-like flowers, rather gangly youngsters. People kept coming up to see what I had and many made comments and asked questions about these "chestnuts". Of course, they weren't chestnuts at all, but buckeyes. A few years ago at the Fairport farmers market I was engaged in a friendly argument with a customer about a particular tree. I was calling it a red horsechestnut, while he insisted it was a buckeye. When I tried to point out that a red buckeye is a completely different plant, he was not convinced.

It was one more paddle in the murky waters of plant names; one more confirmation of the value of those seemingly incomprehensible and unpronounceable Latin/Greek botanical names. Of course, a chestnut is not a chestnut when it's a buckeye (or horsechestnut). Buckeyes belong to the genus Aesculus (esk-you-lus), of the family Hippocastanaceae, while chestnuts belong to the genus Castanea, of the beech family Fagaceae. The term horsechestnut is applied to the European and Asian species, while buckeye refers to American species. The object of the Fairport discussion was actually the red-flowered (or ruby) horsechestnut (Aesculus x carnea), a hybrid of the European horsechestnut (A. hippocastanum) and the American red buckeye (A. pavia). To make matters worse, the flowers of A. x carnea are actually pink. I trust that the picture is now perfectly clear!!

How, you might ask, did all this confusion come about? The answer to that is — seeds. The seeds of buckeyes and horsechestnuts are large, generally round, and shiny chestnut brown, said to resemble the eye of a deer, though I've never been that close to a deer. They also superficially resemble the seeds of chestnuts, being enclosed in a green leathery, sometimes prickly, capsule. They are, of course, inedible, unlike the sweet seed of the true chestnut (Castanea spp.), due to a poisonous compound called aesculin, which is said to cause vomiting, twitching and paralysis (Elias 1989). In England the seeds of the horsechestnut, a common street tree, are prized by boys as weapons in the game of conkers (at least they were when I was a boy, long before computer games and videos). The conker is drilled and strung on a shoelace or string, and is used to swing at the opponent's conker being held in a hanging position, with the intent to break it. The winner is the conker that remains unbroken, and tallies are kept, much like the notches on a gun. Oh for the simple pleasures in life!! There's a lot of cultural baggage that goes along with this, such as soaking the conker in vinegar to harden it (of dubious efficacy).

All of this should go some way to explaining why an article about buckeyes has a title about chestnuts.

Buckeyes and horsechestnuts are some of the most ornamental and yet under-utilised species in American gardens. They are all bold in texture (usually referred to as coarse) and range from the large trees to small multi-stemmed trees and shrubs. All have exceptional, striking flowers, in a multitude of colors, white, pink, red and yellow. All have large, palmately compound (fingered) leaves on long stems (petioles) in an opposite arrangement, lending a tropical appearance to the plants. The buds of some are huge and shiny, some (European and Asian species) sticky, and all tend to open quite early in the spring without any regard for late frosts, which don't seem to faze them in the least. To watch the buds open and the leaves emerge is quite a spectacle. One wonders how all of that stuff could come out of such a small package.

Perhaps the most commonly planted species is the common or European horsechestnut (A. hippocastanum). This tree is native to the Balkans and Turkey, and was introduced into Britain during the Elizabethan era (16^th century), where it proved to be fast-growing, hardy and not particular as to soils (Johnson 1993). The oldest recorded survivor in Britain is in Surrey, planted in 1664, and is about 125 feet high. The horsechestnut is now widely planted in the northeastern US, where it grows well. Unfortunately, it is susceptible to a fungal leaf disease, called leaf blotch, which causes the leaves to turn brown along the margins in summer and drop early. The disease doesn't really bother the tree, because by summer the leaves have done their job anyway, but it is unsightly. The most effective treatment is to rake up the fallen leaves. Most of the trees one is likely to encounter range from about 50 to 80 feet tall, so it is a tree most suited to parks and large estates, rather than the suburban backyard. In early May the sticky buds open and the leaves emerge, followed in late May by the flowers. They are borne on upright terminal panicles from 5 to 12" long. Each flower has 4 or 5 white petals with a blotch of yellow turning to red at the base. The overall effect of a large tree in bloom is outstanding. Many of the uppermost flowers in a single panicle are male, while the lower flowers are perfect (male and female), so that only 2 or 3 seed capsules are produced on each panicle. Each spiny capsule usually contains one or possibly 2 large brown seeds. There is one cultivar of this species generally available; this a double-flowered form, called 'Baumannii', discovered in Switzerland around 1820 (Dirr 1998). The flowers of 'Baumannii" generally last longer than the species, because they are sterile, so that no seed is produced; this is the tree for those people who don't like "messy" trees (i.e. ones that drop stuff on the driveway). Although still attractive in bloom, to my eye the double flowers tend to create a blurring effect and are not as sharp as those of the species. Occasionally, forms of horsechestnut with yellow variegated leaves occur, but these are not always stable.

Another commonly planted street tree is Europe is the ruby or red horsechestnut (A. x carnea). This is a hybrid of A. hippocastanum and the red buckeye (A. pavia), which, unlike most hybrids, comes true from seed. It apparently originated in Germany (Dirr 1998). It tends to be a little shorter in stature and more rounded in outline than the European horsechestnut and branches lower. The flowers are a rose pink with yellow and red splotches. The leaves are darker green than A. hippocastanum and shiny, very similar to those of A. pavia, and are not quite so prone to the leaf blotch. The buds are not sticky and the seed capsules are smooth. This is perhaps one of the most beautiful flowering trees, although it is seldom seen outside arboreta. There is a darker pink variety called 'Briotii' available, generally grafted onto European rootstock. The variety 'Plantierensis' or A. x plantierensis is a pink-flowered seedless form developed in France from a backcross of A. x carnea and A. hippocastanum.

Perhaps the largest tree of the Aesculus genus is the Japanese horsechestnut (A. turbinata). This is very similar to the European species but larger all round. The tree grows to 80 to 100 feet and the leaves are the largest of all the genus, about 3' across with each leaflet approaching 14"long. Like its European cousin, the leaflets are broader and more rounded than the American buckeyes. The flowers are white, similar to the European, but a little creamier. The new growth on the Japanese species is covered with a dense brown indumentum. This is a species for large open areas.

Arguably the most refined of the horsechestnuts is the Himalayan species, Indian horsechestnut (A. indica). This species prospers in England but is generally not seen in the US except perhaps for the northwest. The white flowers occur in June in 12" panicles; individual flowers are wide open with yellow and red blotches. The petioles and pedicels (flower stalks) are red, giving a overall pinkish appearance. A deeper pink variety is 'Sidney Pearce'. The leaves are dark, glossy green and often produce good orange fall color, unlike most horsechestnuts, which tend to turn brown or drop green.

The American continent is home to more species than elsewhere, but few are ever seen in the landscape, due, no doubt, to Americans' preference for exotics. It seems to be true that more native American plants are to be found in European landscapes than in American gardens. Perhaps the most familiar of the American species is the Ohio buckeye (A. glabra), the state tree of Ohio, native of the western Appalachians and the Ohio River Valley to central Texas. This species is also called Fetid Buckeye due to the unpleasant odor produced by the bark, twigs, leaves and flowers. The flowers are a greenish-yellow and more tubular than the non-American species. The leaves generally have 5 leaflets, except for the Texas variety (A. glabra var. arguta), which has 7 to 9 and tends to be more shrubby. The seeds of this species come in a spiny, but blunt, capsule. The Ohio buckeye has quite good orange fall color, but is highly susceptible to leaf blotch.

A more refined American species is the yellow or sweet buckeye (A. flava or octandra). This is a large forest tree of the Appalachians, ranging from southern Pennsylvania to north Georgia. Trees can reach 80' and old specimens have a scaly peeling bark of gray and brown, reminiscent of sycamores. The flowers are yellow and tubular in loose panicles, opening in May. The leaves are bright green, turning clear yellow in fall. Seeds are in a smooth capsule. Although the seeds are supposedly sweet, they still contain the poison, aesculin, which has reportedly sickened livestock. The Indians, however, found that by roasting, mashing and leaching in water, the seeds could be rendered into a nutritious and palatable flour (Elias 1989), similar to the historic use of acorns.

One of my favorite buckeyes is the red buckeye (A. pavia), a small tree or shrub, usually found as an understory species in woods and along streams from Virginia to Louisiana. This is a fast-growing species and flowers when very young, often less than 3' tall. It is also probably the earliest to break bud, in April, although mine have never been damaged by frost in spite of the early budbreak. It also tends to drop its leaves early, in late September, and usually green. The leaves are a dark green and glossy; powdery mildew is sometimes a problem, as is leaf blotch, but neither is too significant. Often growing as a multi-stemmed shrub or small tree, red buckeye matures at about 20' and can be grown in the shade or in full sun. In the shade it tends to be more open. In either situation moisture is a requisite, as for most buckeyes; they do not appreciate dry soils. As the name implies, the June flowers are a deep red, and like most American species tend to be tubular, rather than the trumpets seen on the European and Asian species. This species was one of the parents of the above-described red horsechestnut (A. x carnea) and provided the red color and the glossy leaves, and presumably accounts for the smaller stature of the hybrid.

Sometimes listed as a variety of red buckeye is another shrubby species native to the southeast (A. splendens). It is very similar to red buckeye, with scarlet red flowers, but reportedly has a dense pubescence on the underside of the leaves (Dirr 1998). It should perhaps be noted here that the specimen labelled as A. splendens at the west end of Robinson Drive in Highland Park, Rochester, has clear yellow flowers and is almost certainly A. flava or A. x neglecta, not A. splendens. Whatever the variety it is a beautiful specimen in flower and has excellent orange-yellow fall color.

Painted buckeye (A. sylvatica) is a small tree or shrub, also native to the southeastern woods of the Georgian piedmont. The flowers on this species range from yellow-green to cream to pink to reddish. Cross pollination with A. pavia probably accounts for much of the red coloration. Like the red buckeye, the painted buckeye rarely grows beyond about 20'.

There are a number of hybrids, generally grouped as A. x hybrida. Many of these are crosses of A. pavia and A. flava with red or yellow flowers. Since buckeyes tend to cross quite readily, the resulting hybrids are sometimes difficult to define. A good hybrid for orange-yellow fall color is A. x neglecta (A. flava x A. sylvatica). There appear to be two varieties, 'tomentosa' and 'pubescens', although the differences are not obvious, since both names refer to fine hairs. Flowers are a pale yellow. Another hybrid, well represented in the Highland park collections, is Ellwanger buckeye (A. x woerlitzensis 'Ellwangeri' [{A. flava x A. pavia} x A. sylvatica]). This is a large tree with dark red tubular flowers with creamy-yellow tips.

Perhaps the most unusual of the buckeyes is the shrub, known as bottlebrush buckeye (A. parviflora), native of the southeast. This is a wide-spreading suckering shrub, which should be given plenty of room. It grows to a height of 10 to 12' and forms a dense colony, allowing little competition. The flowers are white held in upright panicles up to 12" long. The flowers appear in mid to late July, unusual for buckeyes, and are more open than the typical tubular buckeye flowers, while the pink stamens with red anthers protrude about 1" beyond the petals. The effect is outstanding, and any gardener with room should grant space for this shrub. Fall color is yellow. Seed production is often sparse unless one hand pollinates the flowers, but propagation by root cuttings is quite simple.

Buckeyes and horsechestnuts come in a wide choice of forms and sizes and are suitable for most gardens. With the exception of Indian horsechestnut (A. indica), the above-described species and varieties are all perfectly hardy in the western New York. Most species like full sun, but some are quite tolerant of shade under larger trees, especially the shrubby A. pavia, A. splendens, and A. parviflora; the last seems to do best under larger trees where it receives morning (eastern) sun, but is shaded from the hotter afternoon (western) sun. Well-drained soil is a requirement and moisture; dry soils produce marginal necrosis on the leaves. Deer can be a problem in some areas, especially in late winter, when the large succulent buds prove too big a temptation. But, in my experience, the damage is minor, resulting in the loss of a few flower buds; soon the trees will be high enough that the flowering buds will be beyond reach. Once established after a season or two, the trees can grow upwards of 2 to 3' a year. They may be difficult to find, however. Few nurseries seem to carry them. They all tend to be tap-rooted, which makes transplanting difficult, unless root-pruning techniques are employed. Propagation by seed is relatively easy, provided the seed is collected when the capsules are opening and are not allowed to dry out. Plant immediately or keep in the refrigerator in a moist medium. In the refrigerator I have found that many seeds will begin to sprout quite early, even in January. It is important to remove the seeds soon after the radicle emerges and pot them up, otherwise the roots become entwined and can begin to rot. Because of the ease with which buckeyes cross-pollinate, collecting seed from under a group of different species almost guarantees some hybridization.

Many fine specimens can be seen in Rochester's Highland Park and Durand-Eastman Park, as well as private gardens around the city of Rochester. In Highland Park there are two main areas to see buckeyes; the west end of the reservoir has an extensive planting of mature trees, mostly A. hippocastanum and varieties, A. glabra, A. x woerlitzensis 'ellwangeri', and A. x carnea, while the west end of Robinson Dr. at Mt. Hope Cemetery has another larger, more varied collection, including the magnificent specimen of European horsechestnut overhanging the road from the cemetery. There is also a large colony of bottlebrush buckeye on the south side of the park above the lilac collection. Durand-Eastman Park also has a few buckeyes, perhaps most notably the rare Texas buckeye (A. glabra var. arguta) along Log Cabin Rd. I would recommend visiting these collections in mid May when most are in bloom, and the bottlebrush in mid July. It is a sight not soon forgotten.