April 3, 2012

Juglans nigra L. - Black Walnut


Black walnut shells are common in archaeological sites in eastern North America. The wood is dark and dense, and was valued in prehistory, as today, for fuel and for furniture. The meat of the nut was highly valued as a source of storable food and oil, and the husk of the fruit, the bark, and the leaves were used as a dye.


Black walnut shell, or pericarp, is distinctive in size (large, thick), shape (oval, shorter than wide) and color (dark brown), and the thick furrowed grooving of the outer surface is unique. The shell is readily distinguished from that of the other common walnut, Juglans cinerea (bitternut), as the latter is typically more oval in shape and possesses a more highly and sharply ridged outer shell. These two corrugated shell types are readily distinguished from the lightly colored, smooth, and slightly veiny shell of the Arizona walnut (J. major). Table 1 provides a metric and qualitative description of eastern United States walnut species' pericarps, similar to the data compiled for the hickories, such that these two Juglandaceae genera may be compared using this manual.

Figure 2. Charred nut shell of Juglans nigra.

Archaeological Distribution

Black walnut shell has been found in most archaeological sites where the tree has historically grown, although it seems to have been much less important than acorn, hickory, and pecan (e.g., Lopinot, 1988). The wood of J. nigra comprised a significant portion of the carbonized wood remains at the Koster Site, between 7.2% and 32.3% in four horizons dated to between 5000 and 2000 B.C. (Asch et al., 1972). Black walnuts contributed to less than 4% of the ample nut shell remains from this site, but were recovered from 24% of the samples and were the third most ubiquitous taxon (after hickory and acorn).

Table 1. Size and Shape Characteristics of Nutshell (pericarp) Morphology in Selected Juglans Species.*

The Plant and its Modern Distribution

Black walnut trees mature slowly, but are resistant to infestation by insects. The walnut grows best in well drained, neutral soils and are commonly found on hillsides and rich mesic bottomlands (Talalay et al. 1984) Black walnut trees can be found in rich woods from Massachusetts west to Minnesota in the north, extending south from Florida to Texas (Brinkman, 1974). The average production of the black walnut in a closed canopy is estimated to be just over four pounds of nuts per tree annually (Talalay et al. 1984). The pinnately compound leaves contain between 11 and 25 alternating leaflets that are smooth on top but downy on the underside. The fruit is large (approximately 7cm in diameter) and rounded, although the subspecies J. nigra oblonga is characterized by a more ovate fruit. The bright green skin-like covering of the fruit is called the husk, or the exocarp (Pearsall, 1989) and it is very difficult to remove manually. The nutshell is robust and corrugated, 4-locular at the top and bottom (Gray 1970). The nut is incompletely divided into chambers (2-4) called cells. The sculptured, indehiscent nut is difficult to access and extract from the hard endocarp, but is highly valued for its distinctive taste and precious oils (Heywood 1993).


A perusal of the literature reveals virtually no end of uses for this hardwood. The nut is aromatic and flavorful, and can be stored for use through the winter, or even several years if kept cool and dry. Walnut oil has been used as fuel for lamps and can be made into butter, although it becomes rancid quickly (Steyermark 1963).

The wood has been celebrated as one of the finest available in North America and is a prized furniture wood. For further information on how to identify carbonized wood , consult Core et al. 1979. The nut shell has also been used as a fuel, and, as with hickory, carbonized shell fragments are abundant in archaeological sites. The fruit and nut stain deeply, and have been historically used as dyes, as have the bark and leaves. Native American ethnobotany has revealed multiple medicinal uses for the bark, leaves, husks, and nuts of this tree, including its utility as a mosquito repellant, a dermatological aid, an antidiarrheal, a laxative, and an anthelminthic. In one form or another, this tree has been used to relieve the symptoms of fever, kidney ailments, gastrointestinal disturbances, ulcers, toothache, syphilis, and snake bite, among others. Western science has shown that the fruit husks of the black walnut contain chemicals that inhibit bacterial and fungal growth, and may be valuable in controlling dermal, mucosal and oral infections in humans (Heisey and Gorham 1992).


Asch, N., R. I. Ford and D. L. Asch
    1972   Paleoethnobotany of the Koster Site: the Archaic Horizons. Illinois Valley Archaeology
            Program, Research Papers, Vol. 6. Illinois State Museums, Springfield.

Brinkman, K. A.
    1974   Juglans L. Walnut. In Seeds of the Woody Plants of the Unites States, pp. 454-459.
            Forest Service, U.S.D.A. Agricultural Handbook No. 450, Washington D.C.

Core, H. A., W. A. Coté and A. C. Day
    1979   Wood Structure and Identification (2nd Edition). Syracuse University Press, Syracuse.

Gray, A.
    1970   Gray’s Manual of Botany. 9th Edition. Van Nostrand, New York.

Heisey, R. M. and B. K. Gorham
    1992   Antimicrobial effects of plant-extracts on Streptococcus mutans, Candida albicans,
            Trichophyton rubrum and other microorganisms. Letters in Applied Microbiology

Heywood, V. H.
    1993   Flowering Plants of the World. Oxford, New York.

Lopinot, N.
    1988   Archaeobotany of Cahokia ICT-II. Draft Report prepared for the Illinois Historic
            Preservation Agency, Springfield.

Pearsall, D. M.
    1989   Paleoethnobotany: a Handbook of Procedures. Academic Press, San Diego.

Steyermark, J. A.
    1963   Flora of Missouri. Iowa State University Press, Ames.

Talalay, L., D. R. Keller and P. J. Munson
    1984   Hickory Nuts, Walnuts, Bitternuts and Hazelnuts: Observations and experiments
            relevant to their aboriginal exploitation in eastern North America. In Experiments and
            Observations on Aboriginal Wild Plant Food Utilization in Eastern North America,
            edited by P. J. Munson, pp. 338-359. Prehistory Research Series, Vol. VI, No. 2.
            Indiana Historical Society, Indianapolis.

Written by: Sarah Walshaw

*The sample is represented by the specimens available in Washington University’s Palaeoethnobotany Laboratory.