Centaurea cyanus (introduced species) nearPeshastin, Chelan County, Washington
Centaurea cyanus, commonly known ascornflower orbachelor's button (among other names),[note 1] is an annualflowering plant in the familyAsteraceae native to Europe. In the past, it often grew as aweed in cornfields (in the broad sense of "corn", referring tograins, such as wheat, barley, rye, or oats), hence its name. It is nowendangered in its native habitat byagricultural intensification, particularly by over-use ofherbicides. However,Centaurea cyanus is now alsonaturalised in many other parts of the world, including North America and parts of Australia through introduction as anornamental plant in gardens and as a seed contaminant in crop seeds.[3]
Flowering shoot of cornflower. I. Disk-floret in vertical section
Centaurea cyanus is anannual plant growing to 20–100 centimetres (8–39 in) tall, with grey-green branched stems. The leaves are lanceolate and 3–10 cm (1–4 in) long.[4] The flowers are most commonly an intense blue colour and arranged inflowerheads (capitula) of 1.5–3 cm diameter, with a ring of a few large, spreading rayflorets surrounding a central cluster of disc florets. The blue pigment isprotocyanin, which in roses is red.[5] Fruits are approx. 3.5 mm long with 2–3 mm-longpappus bristles.[6] It flowers all summer.[7]
Centaurea cyanus is adiploid flower (2n = 24).[8] The genetic diversity within populations is high, although there could be a future decline in diversity due topopulation fragmentation and intensive agriculture.[9] In general,Centaurea cyanus is aself-incompatible species. However,selfing still occurs occasionally, but results ininbreeding depression.[10]
Centaurea cyanus is native totemperate Europe, but is widely naturalized outside its native range.
It has been present in Britain and Ireland as anarchaeophyte (ancient introduction) since theIron Age.[11] In the United Kingdom, it has declined from 264 sites to just 3 sites in the last 50 years.[12]
In reaction to this, the conservation charityPlantlife named it as one of 101 species it would actively work to bring 'back from the brink'.[13]
In theCounty Clare (VC H9) inIreland,C. cyanus is recorded in arable fields as very rare and almost extinct,[14] while in northeast Ireland, it was abundant before the 1930s.[15]
Centaurea cyanus is considered a noxiousweed in arable crops, especiallycereals andrapeseed.[16] Inwinter wheat, one plant per m2 can cause a yield loss of up to 30 kg / ha.[17]Centaurea cyanus produces around 800 seed per plant, which are either shed shortly before the harvest ofcereals, or they are threshed together with the cereal grains, contributing to the further spread of the species by the harvesting machinery and contaminated seed. The occurrence ofCentaurea cyanus strongly decreased during the last decades due to improved seed cleaning, more intensive nitrogen fertilization andherbicide use. However,Centaurea cyanus has become more common in cropland due to an increase incrop rotations dominated bywinter cereals andrapeseed and the use of more selective herbicides with a low effectiveness againstCentaurea cyanus.[16] In addition, the emergence of resistance against the herbicide class ofsulfonylureas has been reported recently.[18] Due to its strong roots,Centaurea cyanus is difficult to control mechanically in spring.[16]
Thepollen ofCentaurea cyanus is used by several different insect species. Insects of the ordersHymenoptera andDiptera are particularly attracted by the flower.[19] AsCentaurea cyanus is aself-incompatible species, it needs externalpollination. Thenectar ofCentaurea cyanus is very sweet with a sugar content of 34%. Due to its high sugar production of up to 0.2 mg sugar per day and flower, the species is highly appreciated bybeekeepers.[20]
The seeds ofCentaurea cyanus are one of the favourite foods of theEuropean goldfinch.
Centaurea cyanus was found to produce volatiles attractingMicroplitis mediator,[21] which is a majorparasitoid of the cabbage moth (Mamestra brassicae), which is the most important pest ofcabbage (Brassica oleracea) in central Europe. PlantingCentaurea cyanus in cabbage fields as acompanion plant was thus suggested as an alternative to the widespread use ofinsecticides to controlMamestra brassicae. Field experiments showed that plantingCentaurea cyanus in cabbage fields at a density of 1 plant / m2 can result in a significant increase in parasitation ofMamestra brassicae larvae, predation ofMamestra brassicae eggs (e.g. bycarabid beetles orspiders) and ultimately cabbage yield.[22]
Severalcultivars ofCentaurea cyanus with varyingpastel colours, including pink and purple, have been selected for ornamental purposes. The species is also grown for thecut flower industry in Canada for use by florists. Doubled bluecultivars (such as 'Blue Boy' or 'Blue Diadem') are most commonly used for this purpose, but white, pink, lavender and black (actually a very darkmaroon)cultivars are also used, albeit to a lesser extent.
As for all ornamental plants, important goals ofCentaurea cyanus breeding include the induction of phenotypic variation (e.g. in flower coloration, size and shape, foliage characteristics or plant height), higher flower yield, resistance to pests and diseases as well as tolerance to abiotic stress (e.g., extreme temperatures, drought or salinity).[23]
Centaurea cyanus requires full sun and neutral (pH 6.6–7.5) to mildly alkaline (pH 7.6–7.8), moist and well-drainedsoil. However,Centaurea cyanus is quite tolerant to drought once established.[24]
For summer-blooming plants,sowing should be executed in late spring. In moderate climates, however, it is also possible to sow Centaurea cyanus in early fall. In this case, plants will already start to flower in the following spring. Recommended spacing between plants is approx. 20 to 30 cm.[24]Centaurea cyanus cangerminate from up to 10 cm depth, but the best result is obtained at 1 cmsowing depth.[25] Germination occurs quickly after sowing.
Highphosphorus fertilization in mid-summer will increase flower production.Mulching is recommended to prevent drying out of the soil and exposure of the root system to the sun.[24]
Seeds are harvested either by hand or, in an agricultural setting, with a seed harvesting machine. On average there are 97,000 seeds in a pound of cornflower seeds.[27]
Hand collecting can be time-consuming and yields are rather low.
A seed harvesting machine is more efficient than collecting the seeds by hand, but it is costly. The main principle of such a machine is that it brushes the ripe seeds off the plant and creates across flow fan action that generates sufficient air velocity to hold and gather the seeds into the seed bunker.[28]
Deadheading will encourage the plant to produce more blooms. Cornflowers are often used for ornamental purposes and by cutting them, up to their third leaves, they will produce more blooms and grow a bigger stem.
Raw cornflower petals used as a dessert decoration ingredient on strawberry ice cream
The flowers ofCentaurea cyanus can be eaten raw, dried or cooked.[29] Driedpetals are used in foods, including in spices. Their main purpose is to add colour to food. There are cheeses or oils that contain raw petals. Petals can also be added to salads, drinks, and desserts for garnishing purposes in raw or dried form.
Dried petals are also used in teas and other beverages. Blue cornflower petals are sometimes one of the ingredients inLady Grey tea.[30]
Centaurea cyanus contains a wide range of pharmacologically active compounds, such asflavonoids,anthocyanins andaromatic acids.[31] Especially the flower head finds application in herbal medicine, but leaves and seeds are also used for pharmacological purposes, albeit to a lesser extent.
The blue color ofCentaurea cyanus is due toprotocyanin, ananthocyanin pigment that is also found in roses.[35] Different anthocyanins derived fromCentaurea cyanus are used as natural additives in food products, such as yoghurts.
Centaurea cyanus has been evaluated forphytoremediation of soils contaminated withlead. Inoculation of the contaminated soil withGlomus spp. (fungus) andPseudomonas spp. (bacterium) would significantly enhance the biomass production and lead uptake ofCentaurea cyanus.[36]
In folklore, cornflowers were worn by young men in love;[clarification needed] if the flower faded too quickly, it was taken as a sign that the man's love was not returned.[37]: 126
The blue cornflower was one of the national symbols of Germany.[38] This is partly due to the story that whenQueen Louise of Prussia was fleeing Berlin and pursued byNapoleon's forces, she hid her children in a field of cornflowers and kept them quiet by weaving wreaths for them from the flowers. The flower thus became identified withPrussia, not least because it was the same color as the Prussian military uniform.[39] After the unification of Germany in 1871, it went on to become a symbol of the country as a whole. For this reason, inAustria the blue cornflower is a political symbol forpan-German andrightist ideas.[40][41] It was worn as a secret symbol identifying members of the then-illegalNSDAP in Austria in the 1930s.[42][43] Members of theFreedom Party wore it at the openings of the Austrian parliament since 2006.[44][45][46] After the last general election 2017 they replaced it with theedelweiss.[47]
It was also the favourite flower of Louise's sonKaiser Wilhelm I.[48] Because of its ties to royalty, authors such asTheodor Fontane have used it symbolically, often sarcastically, to comment on the social and political climate of the time.[citation needed]
The blue cornflower has been the national flower ofEstonia since 1969 and symbolizes daily bread to Estonians. It is also the symbol of the EstonianConservative People's Party.
A blue cornflower was used byCorning Glass Works for the initial release of Corning WarePyroceram cookware. Its popularity in the United States, Canada, United Kingdom and Australia was so high that it became the symbol of Corning Glass Works.
^Martin E., Dinç M., Duran A. (2009). "Karyomorphological Study of Eight Centaurea L. Taxa (Asteraceae) from Turkey".Turkish Journal of Botany33:97–104.
^Le Corre V., Bellanger S., Guillemin J.-P., Darmency H. (2014). "Genetic diversity of the declining arable plant Centaurea cyanus: Population fragmentation within an agricultural landscape is not associated with enhanced spatial genetic structure".Weed Research54:436–444.
^Bellanger, Solène; Guillemin, Jean-Philippe; Touzeau, Solène; Darmency, Henri (2015). "Variation of inbreeding depression in Centaurea cyanus L., a self-incompatible species".Flora.212:24–29.Bibcode:2015FMDFE.212...24B.doi:10.1016/j.flora.2015.02.003.
^Skeffington, M.S. (2015). "Cornflower (Centaurea cynanus L.) and Good-king-henry (Chenopodium bonus-henricus L.)".Irish Naturalists' Journal.34:27–31.
^Hackney, P. (1992).Stewart & Corry's Flora of the North-east of Ireland (Third ed.). Institute of Irish Studies and The Queen's University of Belfast.ISBN0-85389-446-9.
^abcGehring, K.; Seemann, W.; Thyssen, S."Leitunkräuter in Getreide".LfL Bayern. Bayerische Landesanstalt für Landwirtschaft. Retrieved26 July 2020.
^Pallutt, B.; Flatter, A. (1998). "Variability of weed competitiveness in cereals and consequences for the correctness of thresholds".Journal of Plant Diseases and Protection (Special Issue 16):333–344.
^Adamczewski, K.; Kierzek, R. (2010). "Cornflower (Centaurea cyanus L.) cross resistant on ALS inhibitors".Progress in Plant Protection.50 (1):285–290.
^Carreck N., Williams I. (2002). "Food for insect pollinators on farmland: insect visits to flowers of annual seed mixtures". Journal of Insect Conservation 6:13–23.
^Helmut Horn, Cord Lüllmann: Das große Honigbuch, Kosmos, Stuttgart, 3. Auflage, 2006,ISBN3-440-10838-4, S. 31
^Rop O., Mlcek J., Jurikova T., Neugebauerová J., Vabkova J. (2012). "Edible Flowers-A New Promising Source of Mineral Elements in Human Nutrition".Molecules17:6672–83.
^Al-Snafi A. (2015). "The pharmacological importance of Centaurea cynus - A review".International Journal of Pharmacy Review and Research5:379–384.
^Garbacki N., Gloaguen V., Damas J., Bodart P., Tits M., Angenot L. (1999). "Anti-inflammatory and immunological effects of Centaurea cyanus flower-heads".Journal of ethnopharmacology68:235–241.
^Lockowandt L., Pinela J., Roriz C., Pereira C., Abreu R., Calhelha R., Alves M., Barros L., Bredol M., Ferreira I. (2019). "Chemical features and bioactivities of cornflower (Centaurea cyanus L.) capitula: The blue flowers and the unexplored non-edible part".Industrial Crops and Products128:496–503.
^Pirvu L., Dragomir C., Schiopu S., Mihul S. (2012). "Vegetal extracts with gastroprotective activity. Part. I. Extracts obtained from Centaurea cyanus L. raw material".Romanian Biotechnological Letters17:7169-7176.
^Shiono M., Matsugaki N., Takeda K. (2005). "Structure of the blue cornflower pigment".Nature436:791–791.
^Karimi, Akbar; Khodaverdiloo, Habib; Rasouli-Sadaghiani, Habib (2018). "Microbial-Enhanced Phytoremediation of Lead Contaminated Calcareous Soil by Centaurea cyanus L.".CLEAN - Soil, Air, Water.46 (2).Bibcode:2018CSAW...4600665K.doi:10.1002/clen.201700665.
^Howard, Michael (1987).Traditional Folk Remedies. Century.
^"Porter le Bleuet de France" [Wearing French Cornflower].Le Bleuet de France [French cornflower] (in French).Archived from the original on 24 May 2023. Retrieved11 June 2023.Depuis sa création en 1920, le Bleuet de France est le symbole de la mémoire et de la solidarité des français envers les anciens combattants, les victimes de guerre, les veuves et les orphelins. Il se porte sur le côté gauche, côté du cœur, chaque 8 mai et 11 novembre. [Since its creation in 1920, the Bleuet de France has been the symbol of the memory and solidarity of the French towards veterans, war victims, widows and orphans. It is worn on the left side, side of the heart, every May 8 and November 11.]
