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'Non-invasive' cultivar? Buyer beware

October 11, 2011
American Institute of Biological Sciences
Cultivars of popular woody ornamental plants that have reduced viable seed production and are being advertised as "non-invasive" in the horticultural and nursery industries are probably nonetheless quite capable of spawning invasions, according to researchers. More rigorous testing, or complete sterility, should be required to allow claims that a cultivar of a potentially invasive species is environmentally safe.

Cultivars of popular ornamental woody plants that are being sold in the United States as non-invasive are probably anything but, according to an analysis by botanical researchers published in the October issue of BioScience. Tiffany M. Knight of Washington University in St. Louis, Missouri, and her coauthors at the Chicago Botanic Garden write that the claims of environmental safety are in most cases based on misleading demographic evidence that greatly underestimates the plants' invasive potential. What is more, the offspring of cultivars do not usually "breed true" and may be more fecund than their parents, especially if they cross with plants from nearby feral populations.

Many invasive plants were once ornamental cultivars, because the characteristics that the "green" industry looks for are the same ones that make a plant potentially invasive -- being adaptable to wide range of conditions, forming dense stands good for erosion control, and having a long flowering period, for example. In recent years the nursery and horticultural industries have responded by creating cultivars of top-selling plants that produce reduced numbers of viable seed and are advertized as "safe to natural areas." Such cultivars of Japanese barberry, buckthorn, and burning bush are now widely sold, as they avoid bans on growing invasive species.

Yet simple population modeling demonstrates that reductions of even 95 percent in the number of viable seed will leave a long-lived species quite capable of spreading -- and many of the new cultivars do not achieve even that much of a reduction. More sophisticated modeling would likely reveal even stronger invasive potential of the "safe" cultivars. Knight and her co-authors conclude that only completely sterile cultivars can be considered truly safe without further testing, and that other types should be tested for breeding true and having a low growth rate before they are sold as non-invasive.

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Journal Reference:

  1. Tiffany M. Knight, Kayri Havens, and Pati Vitt. Will the Use of Less Fecund Cultivars Reduce the Invasiveness of Perennial Plants? BioScience, October 2011

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American Institute of Biological Sciences. "'Non-invasive' cultivar? Buyer beware." ScienceDaily. ScienceDaily, 11 October 2011. <>.
American Institute of Biological Sciences. (2011, October 11). 'Non-invasive' cultivar? Buyer beware. ScienceDaily. Retrieved June 24, 2024 from
American Institute of Biological Sciences. "'Non-invasive' cultivar? Buyer beware." ScienceDaily. (accessed June 24, 2024).

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