|Berberis thunbergii shoot with fruit|
Berberis thunbergii, the Japanese barberry, Thunberg's barberry, or red barberry, is a species of flowering plant in the barberry family Berberidaceae, native to Japan and eastern Asia, though widely naturalized in China and North America, where it has become problematic invasive in many places, leading to declines in species diversity, increased tick habitat, and soil changes. Growing to 1 m (3.3 ft) tall by 2.5 m (8.2 ft) broad, it is a small deciduous shrub with green leaves turning red in the autumn, brilliant red fruits in autumn and pale yellow flowers in spring.
B. thunbergii has deeply grooved, brown, spiny branches with a single (occasionally tridentine) spine (actually a highly modified leaf) at each shoot node. The leaves are green to blue-green (reddish or purple in some horticultural variants), very small, spatula to oval shaped, 12–24 mm long and 3–15 mm broad; they are produced in clusters of 2–6 on a dwarf shoot in the axil of each spine. The flowers are pale yellow, 5–8 mm diameter, produced in drooping 1–1.5 cm long umbrella-shaped clusters of 2–5; flowering is from mid spring to early summer. The edible fruit is a glossy bright red to orange-red, ovoid berry 7–10 mm long and 4–7 mm broad, containing a single seed. They mature during late summer and fall and persist through the winter.
This species is sometimes confused with Berberis canadensis (American barberry), Berberis vulgaris (common or European barberry), and other deciduous Berberis species; it is most readily distinguished by the flowers being produced in umbels, not racemes.
Berberis thunbergii is widely grown as an ornamental plant, both in Japan and elsewhere in the temperate Northern Hemisphere. Numerous cultivars have been selected, including plants selected for yellow, dark red to violet, or variegated foliage, erect growth (for hedge use), and dwarf size.
- B. thunbergii 'Fireball'
- B. thunbergii 'Maria'
- B. thunbergii f. atropurpurea 'Admiration'
- B. thunbergii f. atropurpurea 'Atropurpurea Nana'
- B. thunbergii f. atropurpurea 'Concorde'
- B. thunbergii f. atropurpurea 'Dart's Red Lady'
- B. thunbergii f. atropurpurea 'Golden Ring'
- B. thunbergii f. atropurpurea 'Harlequin'
- B. thunbergii f. atropurpurea 'Rose Glow'
Japanese barberry can be found in most northeastern and Great Lakes states of the United States. A current map of its distribution can be found at the Early Detection and Distribution Mapping System (EDDmapS). In recent years, Berberis thunbergii has been recognized as an invasive species in many parts of the eastern United States. The Plant Conservation Alliance's Alien Plant Working Group lists it among its "Least Wanted". Japanese barberry is prohibited from being a seed contaminant in Michigan and banned from sale in Massachusetts. This species is ranked (Very High) on the New York State Threat Assessment scale.
This Berberis is avoided by deer, and has been replacing native species. Furthermore, the plant can raise the pH of the soil and affect soil nitrogen levels. Unlike B. canadensis and B. vulgaris, B. thunbergii does not act as a host for Puccinia graminis (black rust), a rust pathogen of wheat. B. thunbergii, however, naturally hybridizes with B. vulgaris, and the offspring can be susceptible to P. graminis. 
Japanese barberry provides an exceptionally favorable environment for ticks due to the high humidity present in barberry's dense foliage. It is hypothesized that spread of barberry is correlated with the spread of Lyme disease. Tick numbers are higher in areas with thick barberry understories, as opposed to areas with controlled barberry or no barberry. In one study, 280 ± 51 adult black-legged ticks, Ixodes scapularis, were found per hectare in a barberry infected area, while only 30 ± 10 adult black-legged ticks were found per hectare in otherwise similar area with no barberry present.
Detailed information on how to control Japanese barberry is available in a Michigan Department of Natural Resources document.
- "Moonshine Designs Nursery". Archived from the original on 2 April 2008. Retrieved 29 March 2008.
- "Berberis thunbergii in Flora of China @ efloras.org". efloras.org.
- "Berberis thunbergii in Flora of North America @ efloras.org". efloras.org.
- Swearingen, Jil M. (7 July 2009). "Least Wanted: Japanese Barberry". U.S. National Park Service. Retrieved 20 March 2011.
- Brickell, Christopher, ed. (2008). The Royal Horticultural Society A-Z Encyclopedia of Garden Plants. United Kingdom: Dorling Kindersley. ISBN 9781405332965.
- Michigan Department of Natural Resources: "Invasive Species—Best Control Practices, Japanese barberry."
- "RHS Plant Selector – Berberis thunbergii". Retrieved 12 June 2013.
- "RHS Plantfinder – Berberis thunbergii 'Fireball'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii 'Maria'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Admiration'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Atropurpurea Nana'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Concorde'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Dart's Red Lady'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Golden Ring'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Harlequin'". Royal Horticultural Society. Retrieved 21 January 2018.
- "RHS Plantfinder – Berberis thunbergii f. atropurpurea 'Rose Glow'". Royal Horticultural Society. Retrieved 21 January 2018.
- EDDMapS. 2019. Early Detection & Distribution Mapping System. The University of Georgia - Center for Invasive Species and Ecosystem Health. Available online at "http://www.eddmaps.org/"; last accessed 27 October 2019.
- "PCA Alien Plant Working Group - Japanese Barberry (Berberis thunbergii)". Archived from the original on 23 October 2004.
- "Berberis thunbergii". USDA plant database. Retrieved 8 November 2015.
- "Japanese Barberry". Adirondack Park Invasive Plant Program. Retrieved 1 November 2019.
- Bartaula, Radhika (26 February 2018). "An interspecific barberry hybrid enables genetic dissection of non-host resistance to the stem rust pathogen Puccinia graminis". Journal of Experimental Botany. 69 (10): 2483–2493. doi:10.1093/jxb/ery066. PMC 5920301. PMID 29529250.
- Zimmer, Carl (30 April 2013). "The Rise of the Tick".
- Managing Japanese Barberry (Ranunculales: Berberidaceae) Infestations Reduces Blacklegged Tick (Acari: Ixodidae) Abundance and Infection Prevalence With Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) Scott C. Williams, Jeffrey S. Ward, Thomas E. Worthley, Kirby C. Stafford, III. Environmental Entomology, Volume 38, Issue 4, 1 August 2009, Pages 977–984, https://doi.org/10.1603/022.038.0404.
- Effects of Japanese Barberry (Ranunculales: Berberidaceae) Removal and Resulting Microclimatic Changes on Ixodes scapularis (Acari: Ixodidae) Abundances in Connecticut, Usa Scott C. Williams, Jeffrey S. Ward. Environmental Entomology, Volume 39, Issue 6, 1 December 2010, Pages 1911–1921, https://doi.org/10.1603/EN10131.
- Japanese barberry, https://mnfi.anr.msu.edu/invasive-species/JapaneseBarberryBCP.pdf
|Wikimedia Commons has media related to Berberis thunbergii.|
- US National Park Service: Berberis thunbergii (deals with the species as an invasive species)
- Native Wildlife Garden (concerning lyme disease in relation to barberry stands)
- Species Profile - Japanese Barberry (Berberis thunbergii). National Invasive Species Information Center, United States National Agricultural Library.
- Invasive Species—Best Control Practices, Japanese barberry Michigan Department of Natural Resources.