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The Itinerant Tree
| Article
# : |
10947 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
5 / 1993 |
1,810 Words |
| Author
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Bruce Bongarten
Bruce Bongarten is associate professor of forest biology at
the University of Georgia in Athens and a contractor to the
U.S. Department of Energy for the development of black locust
as an alternative fuel source. |
For seventeenth-and eighteenth-century naturalists the American frontier was a treasure trove of botanical splendors. Among these was a tree with profuse clusters of fragrant, showy white flowers. It was discovered by Jean Robin and son Vespasien, herbalists to King Henry IV of France, and imported to the gardens of Versailles just after 1600. In 1753 it was named Robinia pseudoacacia, in honor of the Robins. Commonly, however, it is known as black locust.
The name "locust" was first attached to the species by British colonists at Jamestown, Virginia (circa 1610), who mistook the tree for the Old-World locust (the carob or St. John's bread), the Mediterranean native that they knew from biblical reference. Ironically, in Britain today, the tree is seldom referred to as "locust." Instead, it is called "false-acacia," or simply "acacia," the latter also referring to a group of tree species found in African and Australian savannas.
A special legume
Confusion among these species is common as all belong to the pea or legume family and share many traits. All members of the family, for example, produce similar fruits, which are variations on the pea pod theme. At maturity the fruits are dry and dehiscent, exposing a single cavity with several seeds arranged linearly along one edge. Also, the leaves of black locust and its relatives are similar. They are pinnately compound, that is, they consist of a central stalk with small leaflets arranged on either side in a single plane, much like fern fronds.
Upon close inspection, however, the black locust is easily distinguished. On the twigs of young trees or the lower branches of older trees, two short stout spines guard each node or point of leaf attachment. In most other tree legumes, including the true acacias and the North American honeylocust (Gleditsia triacanthos), the armament is in the form of thorns, which are longer than black locust spines, often branched, and occur singly or in clusters rather than in pairs.
Black locust flowers are also distinctive. About three-quarters of an inch long and resembling pea flowers (somewhat like neck-less swans wearing bibs, if you can imagine that), they have white petals, unlike the three other Robinia species, which have pink flowers. The flowers appear shortly after leaf emergence in spring in pendulous clusters of fifteen to fifty. Some years they can obliterate the foliage from view for up to two weeks.
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