Know Your Natives – Ohio Buckeye

Ohio Buckeye (Aesculus glabra) of the Soapberry (Sapindaceae) Family, formerly of the Horsechestnut (Hippocastanaceae) family, is a medium to large deciduous tree with opposite, palmately compound leaves.  It is native from central Texas to western Pennsylvania and as far north as central Iowa to southern Michigan and south into northern Alabama and the highlands of the northwestern half of Arkansas.  Other common names include “American buckeye” and “fetid buckeye”, based on the odor of crushed leaves, bark and twigs.  The name “buckeye” relates to the dark, ovoid poisonous seeds that have a lighter colored hilum (scar).

Ohio buckeye, with long taproots bearing lateral roots, typically occurs in rich, well-drained soils in sheltered areas of valleys, ravines and slopes in partial to full sunlight.  In shady drier sites, it tends to remain more shrub-like and may reach 15 feet in height, while in sunny favorable sites in Arkansas, it may be 40 feet*.  Trunk diameter remains relatively small at up to about 2 feet.  Large trees in sunny sites have numerous lateral branches that produce a broad rounded crown.  Lower lateral branches are lost in shady sites.  Plants as young as three years old can produce flowers.

Ohio Buckeye - Aesculus glabraPhoto 1:  This 4-inch seedling, in late January, would already have a long taproot.  Seeds in inset were similarly planted outdoors, but had not yet sprouted.

In winter, Ohio buckeye has round tapered lateral or axillary buds with sharp points that grow from just above previous year’s leaf scars. Terminal buds also form on nonflowering shoots.  Buds are covered with six or so layers of tightly imbricated scales with pointed tips.  Scales may have free-standing tips and are slightly keeled at their center.  Most new growth is from the uppermost lateral buds–the terminal inflorescence is shed in the fall or winter, leaving no true terminal bud on the original stem–as well as from terminal buds on sterile stems.   Many lateral buds do not develop. Because the terminal inflorescence is shed after seed dispersal, the dominance of the uppermost lateral buds gives the buckeye crown a very jagged architecture, which is best seen in winter.

In mid to late winter, the most-exterior scales just drop off while inner scales become light green and grow into long, leaf-like appendages before they, too, drop off.  By the time flowers reach anthesis, bud scales are gone and stem growth for the year has mostly stopped.

New stem growth is green and finely pubescent and becomes light gray and glabrous later in the year.  Previous years’ stems bear large, shield-shaped scars where leaves from previous years have dropped off.  Older branches are smooth and gray while larger trees have bark that has small scaly to knotty, unfurrowed plates that uniformly cover the trunk.

When new leaves first unfurl, the opposite leaves are a golden green which evolves to a pale green at time of bloom and a shiny, dark green upper surface in summer while the lower surface is a lighter green.  Leaves, glabrous on upper and lower surfaces, typically have five spreading leaflets, all attached at the tip of the petiole or leaf stalk (palmate), but three leaves and seven leaves may occur.  Leaves have slender, glabrous and light green petioles up to 6 inches long, with a broad clasping base and leaflets that are 3 to 6 inches long.  The central leaflet is the largest and, along with the next two lower leaflets, is at its broadest 1- to 2-inch-width in its upper portion with a gentle taper to its nearly stalkless base and a sharp taper to its apex (somewhat obovate).  The lower two broadly lanceolate leaflets are angled downward within the plane of the leaf.  While the lower portions of leaflets have entire margins, the upper portions have crenulated margins with tiny teeth.  In fall, leaves may become a showy reddish-orange.  Venation of the leaflets is pinnate with straight, equally spaced opposite or offset veins.

New terminal growth of more vigorous stems continues unabated to produce an upright panicle of flowers 6 to 8 inches long.  The peduncle of the inflorescence begins immediately above the last set of new leaves, initially with the same appearance as the stem below.  Above the peduncle, groups of flowers are spread around the rachis with spaces between groups.  Stalks of the floral groups are initially coiled against the rachis, but as growth continues, flower buds enlarge and open and the coils gradually straighten.  Flowers all along the rachis open in unison from the rachis to the ends of the straightened coils. Flowering continues for several weeks.  At the time of bloom, the color of the stem, peduncle, rachis and pedicel are the same light green with very short pubescence.  New stems and rachises become tan with rounded white lenticels (pores) by mid-summer.  Peduncles fall off after seeds mature and the capsules split open.

Ohio Buckeye - Aesculus glabraPhoto 2:  Terminal and lateral buds produce rapid spring growth.  These two stems grew from separate lateral buds at the top of previous year’s growth.

Ohio Buckeye - Aesculus glabraPhoto 3:  This plant, only several years old, produced its first inflorescence.  Note enlarged reddish bud scales about to fall off and (on the trunk) leaf scars, undeveloped buds and lenticels.

Ohio Buckeye - Aesculus glabraPhoto 4:  Opposite leaves typically have five leaflets with pinnate venation and crenulated margins.  Note axillary leaf buds for next years’ growth.

The inch-long greenish yellow flowers, on short pedicels, tend to be mostly male (staminate) with perfect (bisexual) flowers near the base of the cluster.  Flowers have greenish yellow, round and slightly elongated calyxes with five rounded lobes enclosing four greenish yellow petals.  The length of petals protruding from the calyx is greater than the length of the calyx itself.  Two long petals, that are flared upward, may bear orange, feather-like markings extending from flower’s throat to near the petals’ ends.  Two shorter broader petals flare outward in near-horizontal fashion.  Ends of the four petals are roundly flexed toward the flower center.  Flowers have seven stamens with white filaments and brown anthers that are exserted beyond the corolla, and a white pointed pistil (in perfect flowers only) equally exserted beyond the corolla.  The pistil of a flower becomes fully exserted (with open stigma) before the corolla has opened and before stamens are exserted.  Pistils are covered with a fine pubescence while filaments and the exterior of petals have longer hairs.

Ohio Buckeye - Aesculus glabraPhoto 5:  Flowers that are positioned along the upper sides of the clusters.   Pistil of a flower is exserted before flower’s stamens appear, as seen at lower left.

Ovaries of fertilized perfect flowers form green, round, spiky fruits.  Typically, only a few fruits at the base of the panicle will reach maturity.  Mature fruit is an ovoid, thick-skinned and light brown leathery capsule.  The capsule, up 1-½ inches in diameter, contains one to three seeds in separate chambers.  By the time fruit has matured, with multiple seeds, the seed exterior becomes flattened due to seed-to-seed contact.  At dehiscence (splitting of fruit) in late summer, capsules with sharp prickles split, so that the smooth, shiny mahogany-colored seeds with a light tan hilum, drop out.  Seeds, 1 to 1-½ inch wide and long, may germinate where dropped or wherever buried by squirrels or deposited by flowing water.  Seeds can germinate in mid-winter.  With germination, taproot and leaves quickly become fully functional so that cotyledons are not needed for photosynthesis.

Ohio Buckeye - Aesculus glabraPhoto 6:  Fertilized ovaries develop into fruit with long, weak spines.  Typically, only a few fruits per panicle will reach maturity.  Photo in mid-April.

Ohio Buckeye - Aesculus glabraPhoto 7:  Upper portion of panicle beyond developing fruit has dropped off in this mid-July photo.  Note two opposite brown buds at base of panicle’s peduncle (for next year’s growth).

Ohio buckeye can be a desirable garden or wildland plant where people, pets or livestock would not consume the seriously poisonous (contains aesculin) seed or other plant parts (squirrels apparently are not affected).   The plant is quite ornamental with its large attractive leaves, showy flowers and interesting fruit.  It has full-size flower panicles and fruit within several years of being planted by seed.  It also has nice fall color.  It does best in a mesic (moderately and evenly moist) soil where is protected from strong sun and wind.  Leaves may drop early in response to dry, hot conditions.

Red buckeye (Aesculus pavia) is the only other species of the genus native to Arkansas.  Red buckeye, occurring across most of the state, is more shrub-like, with red flowers and smooth seed capsules.  Native to the Appalachians and sometimes cultivated, yellow or big buckeye (Aesculus flava) is dissimilar to Ohio buckeye in various ways, including 1) its lower leaflets extending horizontally, 2) pistil and stamens that are not exserted, 3) fruit capsules that are smooth, and 4) typical height at maturity of 70-90 feet.  Bottlebrush buckeye (Aesculus parviflora) is a species native to the Southeast U.S., primarily Alabama, that is also frequently cultivated.  It differs from Ohio buckeye in having a definite shrubby habit, with multiple stems and suckers from the base, and longer panicles of white flowers with long-exserted filaments.

*  National champion Ohio buckeye in Casey County, KY, is 148 feet tall.

Article and photographs by ANPS member Sid Vogelpohl

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