May 10, 2012

Solanum spp. - Nightshades


Figure 1. Seeds of S. nigrum, S. carolinense  

Solanum is a genus of herbaceous plants, some of which had economic significance in North America pre-contact (Lopinot 1984:498). Seeds are sometimes recovered from archaeobotanical studies, and ethnohistoric accounts document the use of the berries from certain species as food. Worldwide, many nightshades have been economically significant and still are today; some economic species include S. melongena (eggplant), S. tuberosum (potato), S. scabrum (garden huckleberry), and S. lycopersicum (tomato).

    The United States Department of Agriculture (USDA) reports 103 species of Solanum growing in North America today (USDA, NRCS 2008). Many of the species in North America today are introduced and several rarely exist outside of cultivation.


Seeds of wild nightshades tend to be less than 3.0 mm in diameter and flat to slightly concave. They have surface reticulation that varies among species. Seed shape is often oval or broadly elliptic, with some variation. Uncarbonized seeds vary in color from white to brown. Experimental charring often shows a high degree of distortion during carbonization. The variability in morphology and size plasticity within a species and even among seeds within the same berry can make species identification difficult.
    Carolina horse nettle (S. carolinense) has a particularly high level of morphological plasticity (Davis 1993:80). The length range is 1.9 to 2.8 mm, width ranges from 1.4 to 2.1 mm, and thickness varies between 0.6 and 0.8 mm (Davis 1993:80; Montgomery 1977:195). However, Davis (1993:80) notes that the length of fully developed seeds is often significantly less than 2.8 mm. The seed profile in broad view is variable in morphology but roughly ovate. The seed is compressed in cross section, with irregular thickness. The hilum notch is about 1.0 mm long, running along the ventral edge. Surface reticulation is an alveolate pattern. The embryo is coiled and seen three times in cross section (Gunn and Gaffney 1974:26).
    Black nightshade (S. ptychanthum) is a taxon of some confusion. It is morphologically closely related to two other species, both also called black nightshade S. americanum and S. nigrum. Often the three species are clumped under the one taxon S. ptychanthum. Great Plains Flora Association (1986:650) clumps both species into the taxon S. ptycanthum (accurately spelled ptychanthum); they also note that other closely related species, including S. interius and S. scabrum, are part of, what they refer to as “the taxonomically difficult S. nigrum complex” (Great Plains Flora Association 1986:650). However, both the USDA’s National Plants Database (USDA, NRCS 2008) and the Integrated Taxonomic Information System (2008) recognize all three species as separate, but note common overlaps in identification. Due to the similarity in these species, for the purposes of seed morphology description they will be treated here as one. Seed length range is between 1.7 and 2.1 mm, width  range is 1.4 – 1.6 mm, and thickness range is 0.6 – 0.7 mm (Davis 1993:80). Seed profile in broad view is asymmetrically obovate with a blunt radicle tip at one end. In cross section the seed is irregularly elliptical. The hilum is located just below the radicle and is not well defined. The surface appears finely punctuate (minute holes) and at low magnifications may even look psilate (smooth); however, at higher magnifications the characteristic reticulation of the black nightshades is finely areolate (covered with shallow holes). The embryo is coiled and seen three times in cross section (Gunn and Gaffney 1974: 25).

Archaeological Distribution

    Based on his analysis of archaeobotanical and ethnobotanical reports for North America, Lopinot (1984:490-502) accumulated a list of “Potential Plant Food and Beverage Sources of the Carrier Mills Locale.” The data in this report are from a number of archaeobotanical studies; however, Lopinot applies them specifically to his study area in southeastern Illinois between 4000 B.C. and 1000 A.D. He includes both S. americanum and S. carolinense (Lopinot 1984:498). In addition S. americanum is placed in what Lopinot (1988:126) categorizes “Fleshy Fruit Seeds” for the archaeobotanical analysis he conducted at Cahokia. S. americanum appears in a number of samples throughout the temporal span of the Cahokia site from the Lohmann phase to the Mississippian phase (Lopinot 1988). From this assemblage pit feature 264 contained 230 S. americanum seeds; the same feature contains several small masses of seeds which appear to have remains of carbonized fruit pulp still attached (Lopinot 1988:168). Based on these observations, Lopinot (1988:168) argues that the fruits were being collected and brought to Cahokia as food.

The Modern Plant and Its Distribution

     Carolina horse-nettle, horse-nettle, or bull-nettle (S. carolinense) (Figure 2) is a low-growing perennial herbaceous plant with a typical height between 0.3 and 1.3 m (Great Plains Flora Association 1986:647; Peterson and McKenny 1996:324; Steyermark 1981:1313). It is propagated by underground creeping rhizomes as well as by seed dispersal, often involving animals as vectors. The stem is long and not heavily branching; it is covered in 2.0 - 4.0 mm long spines. Blades, which alternate, are up to 10.0 cm long and 8.0 cm wide and widely toothed (Great Plains Flora Association 1986:648). Inflorescences have five to 20 flowers and are cymose (Great Plains Flora Association 1986:648). The corolla is most often violet to purplish blue; however, they may also be white. Steyermark (1981:1313) refers to these two variants as S. carolinense var. carolinense and S. carolinense var. albiflorum (white-flowered). Fruits (berries) are 1.0 – 2.0 cm in diameter and globose turning yellow at full maturity. They fruit from May to October (Peterson and McKenny 1996:324). These plants are found across most of continental North America today (Steyermark 1981:1313; Great Plains Flora Association 1986:647; Peterson and McKenny 1996:324).      

Figure 2. Horse Nettle from USDA Database   


    S. ptychanthum, S. americanum, and S. nigrum (the black nightshades) morphologically are very similar and, as mentioned above, are often clumped under one taxon. Those who see S. ptychanthum and S. nigrum as separate species see these as invasive species from Eurasia, while S. americanum is native to the American west and mid-west. The fruits and seeds of S. nigrum are slightly larger and thicker than their indigenous American relative S. americanum (Steyermark 1981:1312). Morphologically, differentiating between the three is based on a few traits for S. americanum, the undersides of the leaves are green, and berries are speckled white until they turn black when ripe; S. nigrum fruits are large and dark green or purple for S. ptychanthum, the undersides of the leaves are redish-purple. All three are short herbaceous perennials rarely larger than 0.5 m in height and densely branching. Blades are typically 5 – 10 cm long and 3 – 6 cm wide; they are widely, irregularly toothed only at the base. Inflorescence is bunching with multiple berries. Corolla is usually white (Peterson and McKenny 1996:72). Berries are globose and they turn dark when mature. They ripen from May to September (Peterson and McKenny 1996:72).


     Most wild nightshades are described as being poisonous (Kieran 1952; Great Plains Flora Association 1986; Gunn and Gaffney 1974; Steyermark 1981); however, several exceptions apply. Many of the species have berries with low salanine content and are, therefore, edible when ripe. A number of ethnohistoric accounts from North America talk about the use of these berries as food. Gunn and Gaffney (1974:27) report that S. nigrum is one of these species. They also discuss the cultivation of a few separate species of the taxonomically difficult S. nigrum complex all under the common vernacular garden huckleberry (Gunn and Gaffney 1974:27). The ripe, black berries of S. americanum were cooked or eaten raw, sometimes in pies or preserves (Great Plains Flora Association 1986:650; Gunn and Gaffney 1974:25; Steyermark 1981:1312). They often require the addition of sugar to sweeten. The young leaves and stems were also cooked as a pot-herb (Steyermark 1981:1312). However, the unripe berries are poisonous (Steyermark 1981:1312). S. carolinense berries are not edible even when ripe. Gunn and Gaffney (1974:25) claim that the salanine content increases tenfold with maturity.


Davis, Linda W.
     1993    Weed Seeds of the Great Plains: A Handbook for Identification. University Press of
           Kansas, Lawrence, Kansas.
Great Plains Flora Association
     1986    Flora of the Great Plains. University Press of Kansas, Lawrence, Kansas.
Gunn, C. R, and F. B. Gaffney
     1974    Seed Characteristics of 42 Economically Important Species of Solanaceae in the
            United States
. United States Department of Agriculture, Washington D.C.
Integrated Taxonomic Information System
     2008 November 22, 2008, Integrated Taxonomic Information System
Kieran, John
     1952    An Introduction to Wildflowers. Hanover House, Garden City, New York.
Lopinot, Neal H.
     1984    Archaeobotanical Formation Process and Late Middle Archaic Human-Plant
          Interrelationships in the Midcontinental U.S.A. Unpublished Ph.D. Dissertation, Department of Anthropology, Southern Illinois University at Carbondale, Carbondale, Illinois.
     1988    Archaeobotany of Cahokia ICT-II. Draft Report, Prepared for the Illinois Historic
          Preservation Agency, Springfield, Illinois.
Montgomery, F. H.
     1977    Seeds and Fruits of Plants of Eastern Canada and Northeastern United States.
          University of Toronto Press, Buffalo.
     2008. The PLANTS Database,, 22 November 2008, National Plant
          Data Center, Baton Rouge, Louisiana.
Peterson, Roger T., and Margaret McKenny
     1996    Peterson Field Guides Wild Flowers: northeastern/northcentral North America.
          Houghton Mifflin Company, Boston, Massechusetts.
Steyermark, Julian A.
     1981    Flora of Missouri. Iowa State University Press, Ames, Iowa.

Written by: Robert N. Spengler III