Biological Invasions

, Volume 15, Issue 10, pp 2219–2241 | Cite as

Polyploidy and invasion of English ivy (Hedera spp., Araliaceae) in North American forests

Original Paper


Polyploidy is a common feature of agricultural weeds and natural area invaders. There are few studies comparing related diploid and polyploid exotics, however, and it is unclear what ecological and genetic factors favor the establishment of weedy polyploids. This research characterizes the geographic distribution and phenotypic characteristics of diploid Hedera helix and tetraploid Hedera hibernica, European species that are invading North American forests. To confirm the taxonomic affinity of invasive plants, we sequenced five non-coding cpDNA regions for 108 individuals (105 populations) as well as reference samples representing all species in the genus Hedera. Because diploid H. helix and tetraploid H. hibernica are poorly distinguished by morphology and DNA sequence, we used flow cytometry to determine their distribution (585 individuals). More than 90 % of sampled plants had cpDNA sequences identical or similar to H. helix sensu lato and H. hibernica. Diploid H. helix was dominant on the U.S. east coast (78.5 % of sampled plants) while tetraploid H. hibernica was dominant on the U.S. west coast (72.2 % of sampled plants), mirroring the species’ occurrence in maritime versus continental climates of Europe. Moreover, for sympatric occurrences in the Pacific Northwest, H. hibernica was larger and more frequently reproductive than H. helix. In a 2-year garden experiment, tetraploid H. hibernica had substantial architectural differences compared to diploid H. helix, including larger (but less numerous) leaves and thicker (but less branched) stems. Field experiments are needed to evaluate “pre-adaptation” (directional ecological filtering) and other factors mediating the invasion of H. helix and H. hibernica.


Cytogeography Flow cytometry Genome duplication Horticulture Phylogeography Triploidy 



We thank Paul Kron and Brian Husband for assistance with flow cytometry; Erin Fox, Owen Hardy, Rob Laport, and Emily Reiss for help in the field and molecular lab; and Washington State Parks for logistical support and permission to conduct this research. Photo imagery is courtesy of the Washington State Department of Natural Resources, ©1995. Brian Husband, J.J. Le Roux, John Jaenike, Paul Kron, Hugh McAllister, Robert Minckley, Roger del Moral, Dick Olmstead, Suzanne Pierot, Sarah Reichard, Allison Rutherford, Sabina Sulgrove, Russell Windle, and two anonymous reviewers provided helpful comments on a draft of this manuscript. This research was supported by research grants from The American Ivy Society (to TR), Sigma Xi (to TR and to AG), and a National Science Foundation CAREER award (DEB-0953551) and International Research Fellowship (to JR).


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Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Adam F. Green
    • 1
  • Tara S. Ramsey
    • 1
  • Justin Ramsey
    • 1
  1. 1.Department of BiologyUniversity of RochesterRochesterUSA

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