Carya spp. Hickory (thickshelled) Juglandaceae


       Along with the walnuts, hickories are the most economically important members of the Juglandaceae family. Their nuts have been among the most valued, by modern and historic accounts. The nuts of C. illinoensis (pecan), C. ovata (shagbark hickory), C. glabra (pignut hickory), C. tomentosa (mockernut hickory) are prized for their taste, but the nuts of C. microcarpa (small-fruited hickory), C. laciniosa (kingnut or shellbark hickory) are too small, and the bitternut (C. cordiformis) too tart to be considered dietary staples. Carya nutshell has been found in archaeological sites throughout the eastern United States, and is considered to have been an incredibly important plant food prior to the domestication of maize, squash, and beans (Asch and Asch 1985). The bark has been used for furniture and snowshoes, and has served as fuel along with the shell and nut oil.
       Paleoethnobotanists commonly differentiate between thin-shelled (C. cordiformis, C. illinoensis, C. microcarpa, and C. aquatica) and thick-shelled (C. ovata, C. tomentosa, C. laciniosa, and C. glabra) varieties only; however, Lopinot (1982:701) has constructed a chart depicting the “normal curves for nutshell lobe thickness” to differentiate among seven species of hickory. Thick-shelled species have shells that are typically thicker than 2.0 mm at the thinnest point of the lobe, and will be the focus of this entry.

       The fruits of the hickory are rounded to oval in shape, with the thin outer protective covering, the “husk” divided into four lobes that can be broken off to access the nut. The pericarp, the “shell” of the hickory nut, varies widely in size, thickness, color, and texture throughout the genus (see Table 1). Carbonization was found to reduce the thickness of lobes in an experiment conducted by Lopinot (1982), who determined that mockernut hickory (C. tomentosa) reduces by over 20% while shagbark hickory (C. ovata) shrinks by just under 12%. Thus, determining the species of hickory to which a fragment of nutshell can be attributed is not advised using carbonized fragments alone.
       C. ovata bears a nut that is slightly heart-shaped and rounded, and removal of the outer husk reveals a nutshell that is light brown and quite smooth, with visible veining (fine forrowing). The nutshell is the thinnest among the “thickshelled” taxa, with mean shell lobe thicknesses of 1.4 and 2.18 mm in two varieties reported by Lopinot (1982). C. glabra nuts are oval to rounded in shape and are light gray to light brown in color. The smooth outer surface of the shell is only lightly veined. The shell itself is quite thick, between 4 and 7 mm in width. C. tomentosa nuts are oval in shape but have straight sides, being rectangular through the midsection. While the outer surface of the shell is smooth, and corners of the midsection’s “rectangle” are somewhat sharply defined. The shell is quite thick, leaving little room for the endosperm (nutmeat) inside. C. laciniosa possesses the thickest shells (up to 10 mm) of all the hickory species. The shell is oval in shape, light brown in color and is mildly furrowed on its outer surface.

Table 1. Characteristics of  Uncarbonized Shell (pericarp) Morphology in Selected Carya Species.*


(thickness) in mm




Inner Aspect

C. ovata Shagbark

25/20 (1-5)

rounded, heart-shaped

l. brown (ext.)
brown int.

smooth; veined

deep but narrow inner chambers

C. glabra Pignut

25/17 (4-7)

oval but rounded

l. grey/brown, darker inside

smooth, finely veined

thick , little room for nut

C. tomentosa

28/16 (1-4)

oval, rectangular with corners

l. reddish brown (ext.)

Smooth, edges sharp

thick, little room for nut

C. laciniosa

45/30 (6-10)


l. brown (ext.)
brown int.

Smooth, mild furrows

thick, little room for nut

       Carbonized specimens undergo differential shrinkage, as mentioned above, therefore archaeological nut shell fragments are typically put into general categories of “thick-shelled” and “thin-shelled” in lieu of species level distinctions. In this lab, researchers have found 1.00 mm in thickness to serve as a useful but arbitrary dividing line between thin and thick categories of hickory nutshell (<1.00 mm indicating thin-shelled varieties; >1.00 mm categorized as thick-shelled). This simplification is complicated by the observation that pecan shells (the most common of the thin-shelled taxa) may be thicker than 1.00 mm at the ends; similarly, some of the thick-shelled taxa may be thinner than 1.00 mm at the middle section of the fruit. The outer shell surface serves to differentiate between hickory nut shells, which are generally smooth, and walnut shells, which tend to have strong ridging on the outer surface. In specimens where the outer surface is obliterated or not clearly rugose, researchers are advised to employ the family level of taxonomic identification. Acorn shells are very uniform in thickness, unlike hickory shells, which vary in thickness following the curve of the inner septa. Also, hickory nutshell fragments are uniformly dense in cross section, making them easily differentiated from acorn fragments, where a bi-layered pattern is easily visible in cross section.

Archaeological Distribution
Remains of nut shells have been found in archaeological contexts in North America from the Early Archaic (8,000-6,000 B.C.) to the ethnohistoric present (Talalay et al. 1984). Hickory remains have received important attention in the North American palaeoethnobotanical literature, because“[f]all nut harvests, especially thick-shelled hickories (Carya sp.) contributed to settlement stability, as this high energy resource was stored for year-round use” (Asch 1994:28).
       Hickory nut shell was recovered from palaeofecal matter in Salts Cave, Kentucky (Yarnell 1969). With respect to palaeobotanical remains extracted from sediments, “Nut remains are … practically ubiquitous at archaeological sites, with the relative importance of hickory, pecan, black walnut, hazelnut, and acorns varying through time and geographic location” (King 1984:45). Pecan and hickory nut shells dominated the nut assemblages at the Koster site, representing a significant portion of the relatively stable palaeodietary signal from 5000 B.C. to 2000 B.C. (Asch et al. 1972). However, Carya species represent only a small fraction of the wood charcoals found at this site (13% maximum, 1.7% minimum), which is surprising considering the abundance of Carya shell remains and the comparatively high heat value of hickory wood (Asch et al. 1972). In an interesting cost-benefits analysis of nuts and other oak-hickory forest taxa, Christensen (1986) compared acorns with hickory nuts and found that, despite the high benefits and low cost of obtaining both of these resources, hickory nuts predominated archaeological assemblages in the  Eastern Woodlands. Hickory nuts are fairly dense and thick compared with other shells, for instance acorns, and thus are well represented in the archaeological record (Miller 1988), so perhaps the taxon is over-represented in archaeological contexts relative to more fragile nut and acorn remains.

The Plant and its Modern Distribution
       There are approximately one dozen species of Carya native to the United States. The leaves of the shagbark hickory contain 5-7 leaflets (usually 5) which are smooth on the upper surface and downy below. The leaves are 8 to 14 inches long and the margins are finely but sharply serrated. This tree is easily distinguished from other hickories by its grey bark that “exfoliates in long and narrow, shaggy plates, which are loose at the ends” (Grimm 1983 :126). Shellbark hickory trees resembles shagbarks, however the leaves are much larger (15-24 inches long) and contain more leaflets (5-9, usually 7). The leaves are quite furry on the underside, and are finely serrated at the margins. The husk of the shellbark nut is comparatively thick, and the nut itself is encased in a large, thick shell. The mockernut hickory has slightly more oval shaped leaves than those of the shellbark and the shagbark trees, and the leaves contain between 5 and 9 (usually 7) medium sized (8-12 inches long) leaflets. The stems of the leaves are covered with downy hairs. Pignut hickory leaves contain between 5 to 7 leaflets (usually 5) that range from 8 to 12 inches long. Both sides of the leaves are smooth, unlike the species mentioned above. The small nuts of the pignut are bitter and unpalatable, and are seldom eaten.
       The thin but hard dark brown husks of  the mockernut (C. tomentosa), shagbark (C. ovata), pecan (C. illinoensis ) and nutmeg (C. myristicaeformis) hickories split at the base at maturity, normally releasing the nut (shell plus meat, which is the cotyledonary tissue), whereas the endocarps of the pignut (C. glabra), bitternut (C. cordiformis) and water (C. aquatica) hickories split only in the middle and generally cling to the nut even after maturity (Young and Young 1992). C. laciniosa yields approximately 15-25 pounds of nutmeat per 100 pounds of fruit (a 15-25% yield), whereas C. ovata boasts a 25-38% yield, and C. tomentosa yields the highest amount of nut per fruit: 50-80% (Bonner and Maisenhelder 1974).
       The modern range of the shellbark hickory extends in the north from New York state to Nebraska, and south to North Carolina, Alabama, Mississippi and Oklahoma. The shagbark hickory can be found in the north from Maine to Quebec, extending south to Florida and west to Texas. The mockernut ranges from Massachusetts to Michigan in the north, south to Florida and east to Texas (Grimm 1983). The pignut hickory is found in the north from Maine to Minnesota, and in the south from Florida to Texas.

       Contributing to the economic importance of the hickory nut for sustenanceis the fact, in additon to using the nutshell for fuel, Native American groups have employed the bark in an infusion for its diuretic and laxative properties (Moerman 1998). The nut oil, when mixed with bear grease, was used as a mosquito repellant. The nutmeat is high in fat (over 70%) and protein (almost 14%), and is estimated to provide 673 calories per 100 grams of edible nutmeat (Asch et al. 1972:11). The reader is directed to Talalay et al. 1984 for a discussion of the nut yield per tree, and nutmeat yield per fruit, of both the thick-shelled and thin-shelled species.

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Written by: Sarah Walshaw


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