The University of Tennessee - Forest Resources Research and Education Center

The following article was written by Richard Evans, UT Arboretum Director, and originally published in the Volume 22, Number 3 issue of UT Arboretum Society Journal, The Leaflet.

I think our impression of hickory trees is most often registered to the wood. In truth and fable, hickory is as synonymous with "toughness," as oak is with "mighty." Toughness was the characterization of Tennessee's own "Old Hickory" - the nickname of Andrew Jackson, our seventh President of the United States. Accounts of how President Jackson came by that nickname vary. One author ventured, "As a General there was only one word to describe him: indomitable. His men said he was 'tough'. Tougher than most anything they knew. Tough as hickory, someone ventured, which was hard as anyone could suggest … they added the prefix 'old' thereby giving him his everlasting nickname: Old Hickory." Whatever the case, this article is about HICKOR, as in "hickory trees" and is a sequel to my earlier article about oaks (The Leaflet, Vol.21, #3).

In the language of scientists, managers and students of the forest, oaks and hickories are often woven together to describe the most common tapestry of canopy trees that blanket our eastern forest. Forest canopies dominated by a mix of oak and hickory trees are technically referred to as an "Oak-hickory forest cover type" or, "Oak-hickory forest." The Society of American Foresters' (SAF) standard for naming mixed forest cover types ascribes the first name of a "forest cover type" to the dominant (i.e., most common) species and the second name to the second most common - for example, Oak-hickory, Beech-maple, Spruce-fir, etc. Forests dominated by a single species are given the name of that species - for example, "Virginia pine forest."

Hardwood forests of the UT Arboretum, Anderson County, and surrounding counties in Tennessee's Ridge and Valley physiographic provinces, are most likely an Oak-hickory forest type. Oak-pine forest is the second most common eastern forest cover type, and is more common to the Cumberland Mountains and Plateau to the northwest and, the Unaka Mountains to the southeast. In SAF's forest naming scheme, they list no hickory dominated forest cover types (1980. Society of American Foresters. Forest Cover Types of the United States and Canada. 148 pp). Occasionally, hickory may dominant the canopy of small forest stands as a leftover product of previous forest harvesting activities or possibly a natural insect or disease event. However, in the natural scheme of things, where you have hickories you usually have more oaks.

Hickories (Carya sp.) are members of the walnut family (Juglandaceae); however, the differences are easily noted. The stems of our local black and butternut walnut (Juglans nigra and J. cinera, respectively) have chambered piths, the hickory does not; the walnut fruit has indehiscent (does not split open) husk, the hickories have a dehiscent husk; and the walnut's male (staminate) flowers are not branched, the hickories are 3-branched. A much easier way to tell a walnut from a hickory is to crush the leaf and smell the difference. The astringent, yet pleasant order is unforgettable (also, you might notice your hands have turned yellow from the tannin dyes associated with the leaf).

Among hickory species there is another ambiguity - there are two subgenera, the "true hickories" (Eucarya) and the "pecan hickories" (Apocarya). The easiest way to sort out the two subgenera is simply to count the leaflets. The pecan hickories typically have more than seven leaflets, whereas true hickories have seven or less.

In Tennessee there are three pecan hickories - pecan (C. illinoensis) that we associated with a smooth shell, pecan pie, Christmas, and candy; bitternut hickory (C. cordiformis) with it's smaller hard nut and a husk that only splits to the base and is barely fit for squirrels to eat; and water hickory (sometimes called bitter pecan) (C. aquatica) which is somewhat similar to pecan, but with a smaller, more rounded, and bitter nuts.

By far the most common pecan hickory in this area is the bitternut hickory. It can be found growing throughout the UT Arboretum and is most common along ridge tops and on poorer dry sites. West Tennessee is reported to be the general extent for the natural range for pecan. However, the UT Herbarium reports pecan can be found growing in four east Tennessee counties - Marion, Hancock, Sevier, and Blount. Pecan is a desirable tree and has been extensively planted throughout the area. There is a fine pecan tree specimen at the Frozen Head State Natural Area's visitor's center, near Wartburg, and on the UT Campus.

It is unlikely you will see a water hickory if you limit your search to this area. Water hickory is native to swamps and low-lying lands in the western tier of Tennessee counties along the Mississippi River and in Benton County along the Tennessee River.

Identification of the "true" hickories can sometimes be challenging and, comparing description in various textbooks often adds to the confusion. Hickories have a nasty habit of sometimes cross breeding hence, blending identifying characteristics. The experts have met this challenge by periodically changing, adding, or dropping species names or, splitting a species into varieties. To simplify the task at-hand, we will use the UT Herbarium's vascular plants check list and nomenclature as the standard.

The UT Herbarium lists six distinct "true hickory" species common to Tennessee. These species include: Pignut hickory (Carya glabra), Shellbark hickory (C. laciniosa), Carolina hickory (C. ovata var. australis), Shagbark hickory (C. ovata var. ovata), Sand hickory (C. pallida), and Mockernut hickory (C. tomentosa).

The "shaggy" barked hickories are the ones with which most everyone is familiar, although hickories with shaggy bark include shagbark, shellbark and Carolina hickory. The "shaggy" bark hickories have long thin plates of bark that curve away from the trunk and, as a side note, the overhanging shelters created by the loose bark make excellent homes for bats. To easily discern among the "shaggy" barked hickories, you need to have a leaf and/or nut in-hand. The shagbark and Carolina hickory have five leaflets whereas the shellbark has seven, otherwise, the nuts are dissimilar in size - shellbark 1 3/4", shagbark 1 1/2", and Carolina 1". It is most likely that you will find a shagbark hickory at the UT Arboretum and in Anderson County; although, shellbark and Carolina hickories are reported in nearby counties, they are not as common.

The three remaining "true" hickory species not yet discussed - mockernut, pignut and sand hickory - are a little easier to identify. All three of these hickories are common to east Tennessee. Pignut hickory has five leaflets where as mockernut and sand have seven. Mockernut hickory is easily discerned in the winter by its large egg-shaped, yellow to tan terminal bud and, in the summer, by the pubescent (hairy, fuzzy, or "tomentose") leaflet and rachis (leaf stem). Pignut, on the other hand, has a distinctive fruit with a husk that only partially splits to 3/4 the length of the nut. The best recognizable features of sand hickories are the seven leaflets and the thin, hairy, fruit husk covered with minute silvery scales. All three of these hickories can be found growing on poor sites; however, the sand hickory is best adapted to the very worst sandy, rocky and dry sites.

A good tree identification book will aid anyone anxious to search the woods searching for these hickories. Another good reference is the UT Herbarium website (www.bio.utk.edu/botany/herbarium.vascular/vascular.html) for leaf and fruit pictures and the latest nomenclature.

Hickory Hunt