Rhamnus spp. L.

Buckthorn

Rhamnaceae

       About 100 species of Rhamnus grow worldwide, all as shrubs or small trees native to the temperate and warm regions of the Northern Hemisphere, Brazil, and Africa (Hubbard 1974). The fleshy fruits contain several seeds and are used medicinally and as a source for dye. Several species are native to the midsouthern and midwestern United States, although Rhamnus seeds are very rare in the archaeological assemblages of eastern North America.


Description
       Rhamnus seed morphology can differ significantly between species. Rhamnus lanceolata (Figure. 1) possesses a common seed type, an obovoid seed surrounded by a tough seed coat. This coat is indehiscent, although it is often seen splitting at the apex of the seed. The seed coat is difficult to remove, even on seeds dried for over 60 years, and is likely to persist on archaeological specimens. Rhamnus lanceolata seeds measure from 4 to 5 mm in length and 2.5 to 3.5 mm in width with the seed coat present, and slightly smaller with it removed.

       Rhamnus caroliniana seeds (Figure. 2) are larger (4 to 6.5 mm in length, 3.5 to 5.5 mm in width) and more rounded than R. lanceolata, and also possess a seed coat. This seed coat is rarely seen to separate from the inner endosperm, even at the end of a seed. It is similarly durable and persistent, and likely to be present on archaeological specimens.

       The fruits of this genus are similar in appearence to those of Crataegus species, although the seeds are quite different. Although Crataegus seed morphology can differ greatly between individual species, the seeds are generally crescent shaped, with an irregularly convoluted surface and nearly triangular cross section. They are generally also larger than Rhamnus seeds.


Archaeological Distribution
       I could find no published record of Rhamnus in archaeological contexts. The seeds are durable and fairly large, so would be expected to preserve well archaeologically. As a result, we can assume the scarcity of Rhamnus remains is due to their minimal use by prehistoric peoples. Ethnographic accounts indicate possible medicinal use of Rhamnus bark, but this would be almost impossible to detect archaeologically.


The Modern Plant and its Distribution
       Rhamnus plants are woody shrubs or small trees with entire, elliptical leaves (see Figure. 3). R. caroliniana is particularly distinctive, with shiny dark green foliage and red fruits. The two species of Rhamnus (R. lanceolata and R. caroliniana) native to Missouri both grow in open woodlands, often in upland regions, and chiefly in limestone areas. These species range from Texas and Alabama in the south to Ohio, Illinois, and Nebraska in the north. They flower in April to June and fruit from June to August (Steyermark 1963:1026-1028).


Discussion
       Rhamnus cathartica, native to Europe, has historically been used in a variety of ways. The bark, leaves, and fruit contain a purgative substance. The unripe fruits produce a juice which was used for staining maps, and the ripe fruits were used to create the artist’s pigment “sap green” (Steyermark 1963:1027). Several North American species also have been used medicinally. The bark of Rhamnus frangula, a species native to the western United States, has been recently used to remedy constipation and for cleaning the blood, although the fruits of this species are poisonous (King 1984:148). However, the fruits of Rhamnus crocea were eaten by the Apache to go with meat, and the fruits of R. purshiana were recorded as eaten by Indians as well (Yanovsky 1936:42). Today, several species are grown as ornamental hedge plants. The rarity of Rhamnus remains in archaeobotanical assemblages, coupled with their probable durability, indicates that buckthorn was probably not economically important in the prehistoric period.

References
Hubbard, R. L.
    1974   Rhamnus. In Seeds of Woody Plants in the United States. Agriculture Handbook No. 450.
            Forest Service, U.S. Department of Agriculture, Washington D.C. pp.704-708.
King, F. B.
    1984   Plants, People, and Paleoecology: Biotic Communities and Aboriginal Plant Usage in Illinois.
            Illinois State Museum Scientific Papers, Vol. 20. Illinois State Museum Springfield.
Steyermark, J. A.
    1963   Flora of Missouri. Iowa State University Press, Ames.
Yanovsky, E.
    1936   Food Plants of the North American Indians. U.S. Department of Agriculture Miscellaneous
            Publication 237.

Written By: Mac Marston