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The United States Naturalized Flora: Largely the Product of Deliberate Introductions

Richard N. Mack and Marianne Erneberg
Annals of the Missouri Botanical Garden
Vol. 89, No. 2 (Spring, 2002), pp. 176-189
DOI: 10.2307/3298562
Stable URL: http://www.jstor.org/stable/3298562
Page Count: 14
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The United States Naturalized Flora: Largely the Product of Deliberate Introductions
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Abstract

Over the past 400 years plant immigrants have arrived in the United States in huge numbers, the results of accidental and deliberate introduction by humans. Very few immigrations, however, result in naturalizations; the environmental hazards for immigrants in a new range are usually acute and chronic. We traced the history of introduction among the naturalized taxa within a group of U.S. regions and states that span much of the environmental amplitude of the United States. Despite differences among these regions in physical environments and the length of their histories of plant immigration, the proportion of their naturalized floras that likely arrived through deliberate introductions is greater than 50 percent. Many of the first species to become naturalized in the northeastern United States were introduced as food seasonings or putative sources of medicine. Erstwhile ornamentals are prominent components of all the naturalized floras, especially in Florida. Some species introduced as sources of forage or fiber also became naturalized. Before 1900 many now naturalized species were introduced repeatedly and widely into the United States as seed contaminants through an extensive international commerce in crop seeds. The mode of entry is unknown for approximately 30 percent. The likelihood that the majority of species now naturalized in the United States has a history of deliberate introduction and post-immigration cultivation provides a plausible explanation for their persistence in a new range.

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