Buddleja davidii (spelling variantBuddleia davidii), also calledsummer lilac,butterfly-bush, ororange eye, is aspecies of flowering plant in thefamilyScrophulariaceae,native to Sichuan and Hubei provinces in central China, and also Japan.^[1] It is widely used as anornamental plant, and many named varieties are in cultivation. The genus was namedBuddleja after ReverendAdam Buddle, an English botanist. The species namedavidii honors the French missionary and explorer in China, FatherArmand David, who was the first European to report the shrub.^[2] It was found nearYichang by DrAugustine Henry about 1887 and sent to St Petersburg. Another botanist-missionary in China,Jean-André Soulié, sent seed to the French nurseryVilmorin, andB. davidii entered commerce in the 1890s.^[3]

Buddleja davidii
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Lamiales
Family:	Scrophulariaceae
Genus:	Buddleja
Species:	B. davidii
Binomial name
Buddleja davidii Franch.
Synonyms
Buddleja davidii var.albaRehder & E.H.Wilson Buddleja davidii var.magnificaRehder & E.H.Wilson Buddleja davidii var.nanhoensisRehder Buddleja davidii var.superba(de Corte) Rehder & E.H.Wilson Buddleja davidii var.veitchianaRehder Buddleja davidii var.wilsoniiRehder Buddleja shimidzuanaNakai

B. davidii was accorded theRHSAward of Merit (AM) in 1898, and theAward of Garden Merit (AGM) in 1941.^[4]

Buddleja davidii is a vigorous shrub with an arching habit, growing to 5 m (16 ft) in height. The pale brown bark becomes deeply fissured with age. The branches are quadrangular in section, the younger shoots covered in a denseindumentum. The oppositelanceolate leaves are 7–13 cm (3–5 inches) long,tomentose beneath when young. The honey-scented lilac to purpleinflorescences are terminalpanicles, < 20 cm (8 inches) long.^[5] Flowers areperfect (having both male and female parts), hence arehermaphrodite rather thanmonoecious (separate male and female flowers on the same plant) as is often incorrectly stated.Ploidy 2n = 76 (tetraploid).^[6]

In his 1979 revision of the taxonomy of the African and Asiatic species ofBuddleja, the Dutch botanistAnthonius Leeuwenberg sank the six varieties of the species as synonyms of the type, considering them to be within the natural variation of a species, and unworthy of varietal recognition.^[7] It was Leeuwenberg's taxonomy which was adopted in theFlora of China^[8] published in 1996. However, as the distinctions of the former varieties are still widely recognized in horticulture, they are treated separately here:

Buddleja davidii cultivars are much appreciated worldwide as ornamentals and for the value of their flowers as anectar source for many species ofbutterfly. However, the plant does not provide food for butterfly larvae, and buddlejas might out-compete the host plants that caterpillars require.^[9][10]

The species and its cultivars are not able to survive the harsh winters of northern ormontane climates, being killed by temperatures below about −15 to −20 °C (5 to −4 °F).

Younger wood is morefloriferous, so even if frosts do not kill the previous year's growth, the shrub is usually hard-pruned in spring once frosts have finished, to encourage new growth. The removal of spent flower panicles may be undertaken to reduce the nuisance of self-seeding and encourage further flower production; this extends the flowering season which is otherwise limited to about six weeks, although the flowers of the second and third flushes are invariably smaller.

Hardiness:USDA zones 5–9.^[11]

There are approximately 180davidiicultivars, as well as numerous hybrids withB. globosa andB. fallowiana grown in gardens. Many cultivars are of a dwarf habit, growing to no more than 1.5 m (5 feet).

A plant-evaluation manager at theChicago Botanic Garden inGlencoe, Illinois (USDA Hardiness zone 5b) rated nearly 50Buddlejia varieties and cultivars during a six-year trial period, summarizing in 2015 the characteristics of each and the study's findings.^[12] University studies have suggested that nectaring butterflies have greater preferences for someBuddleja cultivators than for others, withLo & Behold 'Blue Chip' and 'Pink Delight' heading a list of eleven.^[13]

Other notable cultivars and hybrids include'Golden Glow' and'Silver Frost'.^[14][15]

Buddleja davidii has been designated as aninvasive species or a "noxious weed" in a number of countries intemperate regions, including the United Kingdom, the Republic of Ireland and New Zealand.^[16] It isnaturalized in Australia^[17] and in many cities of central and southern Europe, where it can spread on open land, railway lines, urban areas and in gardens.

B. davidii was first documented as an invasive species in the United Kingdom during 1922. It is now often seen there along railway lines and on the sites of derelict factories and other buildings.^[18] The plant frequently grew on urban bomb sites during the aftermath ofWorld War II, earning it the nickname of "the bomb site plant".^[19]

B. davidii is widely marketed throughout the United States, where it has reportedly become invasive in some, but not all, areas within which it has been planted.^[20][21][22] Although its flowers feed many native butterflies and other pollinators, plantings of the species are now controversial.^[21][23][24] To prevent seeding and to promote further flowering, its blossoms need to be removed ("deadheaded") as soon as they are spent.^[20]

A number ofBuddleja cultivars have become available that have a variety of sizes and blossom colors and that are either sterile or produce less than 2% viable seed.^{[20][23][25][26]} Thenorthwestern U.S. state ofOregon, which designatedB. davidii as a "noxious weed" and initially prohibited entry, transport, purchase, sale or propagation of all of its varieties, amended itsquarantine in 2009 to permit those cultivars when approved or when proven to be interspecifichybrids.^{[20][23][25][27]} The adjacentstate of Washington has taken actions that are similar to those of Oregon to bring parity to nursery sales between the two states.^[28]

Dennis J. Werner developed the "Lo and Behold"Buddleja hybrid series and the 'Miss Ruby' and 'Miss Violet'Buddleja hybrids atNorth Carolina State University'sJC Raulston Arboretum inRaleigh and at the university's Sandhills Research Station inJackson Springs.^[29] He selected most of the hybrids to have a very low seed-set and to be non-invasive.^[30] Members of the "Lo and Behold" series vary from 30 centimetres (11.8 in) in spread and height to about 1.5 metres (4.9 ft) in height.^[30]

Werner introduced the first of the cultivars (Blue Chip) around 2008.^[30] He derived several of the more recent introductions from his earlier hybrids.^[30] While some, such as "Lo and Behold" 'Blue Chip Jr', 'Ice Chip', 'Lilac Chip' and 'Pink Micro Chip', produce no viable pollen and are highly female-sterile,^[31] the plants are not necessarily fully sterile.^[30] Most were still available in 2022.^[30]

Peter Podaras developed the "Flutterby"Buddleja series during the 2000s while atCornell University's Department of Horticulture inIthaca, New York and patented them in 2011. Podaras selected each of the cultivars for their sterility or low fertility. Although innovative when introduced, several members of the series are no longer commercially available and are rare in cultivation.^[32]Monarch Watch recommends planting only male-sterile "Flutterby" cultivars.^[33]

Vendors have marketed the following "non-invasive"Buddleja cultivars:

•  
  Monarch butterfly feeding on aBuddleja flower,Connecticut, United States
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  Buddleja davidii flowers withpainted lady,peacock and (underneath)small tortoiseshell butterflies
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  Asnowberry clearwing moth carrying pollen on itsproboscis while hovering at aBuddleja blossom
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  Close-up of purpleBuddleja davidii cultivar flowers
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  Close-up of purpleBuddleja davidii flowers photographed in visible, ultraviolet, and infrared light
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  Buddleja davidii 'White Profusion' cultivar flowers
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  Seed capsules
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  Seeds
•  
  Leaves

• Index:Buddleja — forBuddleja davidii cultivars.

• Van Laere K (2008) Interspecific hybridisation in woody ornamentals. PhD. Thesis, Faculty of Bioscience Engineering, Ghent University
• Christenhusz, M.J.M. (2009)."Typification of ornamental plants: Buddleja davidii (Scrophulariaceae)".Phytotaxa.2: 55.doi:10.11646/phytotaxa.2.1.11.
• Franchet, M.A. (1887).Plantae Davidianae ex sinarum imperio, part 2 "Plantes du Thibet Oriental (Province de Moupine)". (Nouvelles Archives du Museum d'Histoire Naturelle Paris), ser. 2, 10: 33-198.
• Li, P. T. & Leeuwenberg, A. J. M. (1996). Loganiaceae, in Wu, Z. & Raven, P. (eds)Flora of China, Vol. 15. Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, USA.ISBN 978-0915279371online at www.efloras.org

• Floridata:Buddleja davidii
• BBC Gardening:Buddleja davidii
• Pacific Island Ecosystems at Risk (PIER):Buddleja davidii
• RHS Buddleja Trials Report