What do we know about the invasive potential of Lonicera caerulea L. cultivars in North America?
Some Eurasian shrubs, including species of Lonicera, have become invasive in North America. Recently, Lonicera caerulea cultivars have been developed from Eurasian germplasm and promoted for North American markets as honeyberry, haskap, or sweetberry honeysuckle. Checklist-based evaluation tools offer insight into the invasive potential of non-native plants introduced to North America, but can be difficult to utilize effectively for taxa with limited cultivation histories. The recent arrival of L. caerulea to North America's horticulture trade makes it difficult to answer questions that rely on an established history of ecological interactions in an introduced range. The only ecological observation that we have found in North America is a 2011 report of a naturalized woodland population of reproductive honeyberry shrubs in Minnesota. However, in northern Europe, the Norwegian Biodiversity Information Centre reported that Eurasian L. caerulea has spread rapidly from planted localities, and poses risks of severe impacts to Norway's natural plant communities. Our best interpretation of available data used in two risk-assessment tools developed for North America indicates that cultivars of Eurasian L. caerulea pose a high risk of invasiveness. A complicating factor is the native occurrence of the closely related mountain fly honeysuckle [Lonicera caerulea subsp. villosa (Michx.) Á. Löve & D. Löve] and blue fly honeysuckle [Lonicera caerulea subsp. cauriana (Fernald) B. Boivin] in portions of North America where cultivars of Eurasian L. caerulea have been promoted. Fly honeysuckles tend to be sporadic, small in stature, and not particularly productive; conversely, Eurasian cultivars have been hybridized and selected for rapid growth and high yield. Unanswered concerns include: (1) should L. caerulea germplasm from Eurasia be considered native in North America; (2) could hybrid, Eurasian genotypes of L. caerulea exhibit greater competitive fitness than the North American fly honeysuckles; and (3) will the introduction of Eurasian L. caerulea cultivars have population genetic consequences for indigenous fly honeysuckles?