Centaurea cyanus

Daisy & Dandelion Family [Asteraceae]

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13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
Up to 2 feet tall with long thin branched stem having very narrow lanceolate leaves which are almost grass-like and alternately peel off the stems at intervals.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
The 'purest' specimens have seven sky-blue ray-florets around the periphery and a smattering of rather long indigo-coloured disc florets in the middle. This one has more than seven, and is a slightly deeper sky-blue.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
The ray florets flare out horn-like with nominally five fairly deeply cut points. The petals of the disc florets in the middle are (unusual for an asteraceae) long and also splayed out.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
The indigo-coloured disc florets are highly curled.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
Apparently, despite splaying outwards like ray-florets do (but un-like those in not being planar, but conical), these are still disc-florets (with nominally 5 flowers ber disc - but this specimen has approximately 8 per disc-floret). Lacking obvious or hidden stamens/anthers and stigma/styles these disc-florets of this particular specimen are sterile. Cornflower is most unusual in these respects.  Capitulum Structure of Cornflower [pdf]. Cornflower is classified as self-incompatible, unable to fertilise itself, but that does not mean it is sterile - it can fertilise neighbouring Cornflowers.

30th Aug 2009, Philips Park, Prestwich, Lancs. Photo: © RWD
From beneath the flower consists of pale-blue radial ray-florets emerging from the top of a Knapweed-type bud, with scaly phyllaries.

30th Aug 2009, Philips Park, Prestwich, Lancs. Photo: © RWD
From above, the disc florets are unusually large for an asteraceae and consist of a curved, indigo-coloured central style emerging from a mauve-coloured sheath that is deeply cut into five narrow petals that splay out at right-angles. Most wind and rain battered specimens do not show this construction clearly. Here there are five disc florets only.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
The phyllaries are green, brown-edged and with short triangular-shaped teeth. The shape of the bud is more like a vase and not globular like that of Greater Knapweed.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
The plant from above. Stems and leaves narrow.


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13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
Not only does it have more than one row of ray-florets, the ray florets are more mauvish than sky-blue. The stem is also much more swollen beneath the flowerhead.

13th July 2011, Blackleach Country Park, Walkden. Photo: © RWD
But this is not a small version of Perennial Cornflower. Note un-opened bud top left.

Not to be semantically confused with: Common Centaury (Centaurium erythraea) nor with similar Centauries such as Seaside Centaury (Centaurium littorale) [plants whose scientific names are similar, but which are in a totally different Family altogether, the Gentian Family (Gentianaceae)].

Not to be confused with : Cornflour [a flour produced from Corn made famous by Brown and Poulson].

Many similarities to : Perennial Cornflower, but that is a perennial whereas Cornflower is an annual. Cornflower is a lot smaller, with outer ray-florets that are shorter and which flare-out wider and are less deeply cut than is Perennial Cornflower.

Uniquely identifiable characteristics

Distinguishing Feature : The typically seven, trumpet-shaped, fairly-deeply cut, radially arranged, pale-sky-blue ray-florets. It takes its specific epithet (second part of the scientific name) cyanus from the colour of the flower (cyan).

No relation to : Corn Marigold, Corn Sow-thistle, Corn Chamomile, Corn Spurrey, Corn Mint, Corncockle nor Turkey-corn [plants with similar names].

Un-like the otherwise similar Greater Knapweed, Common Knapweed and Lesser Knapweed (now known as Chalk Knapweed (Centaurea debeauxii)), there are no versions of Cornflowers that do not have rayed florets. Another difference is that the ray florets are pale-sky-blue rather than the purple of Knapweeds (when present).

It is an archaeopyhte, not native to the UK, but accidentally imported here as a contaminant of crop seed from the Middle East via the Mediterranean some thousands of years ago, so long ago, no one actually knows when.

Once plentiful in both meadows and amidst crops Cornflowers have all but died out in the wild, a consequence of modern farming practices such as the enrichment of soils with fertilisers and extensive use of herbicides to control weeds in farming. It used to be a troublesome weed on arable land, hence the use of herbicides to control it and other arable weeds.

They had become nationally scare by the 1970's, and are now all but extinct in the UK (but thrive one the continent), apart from just several isolated places. One, the arable weed reserve where soil from a field that has never ever been treated with herbicides was transplanted there. Cornflowers, poppies, corncockles and other once extant wild flowers typical of arable fields and meadows are now growing there. In the UK Cornflower is classed as Endangered. Cornflower is being re-introduced in a number of locations.

Cornflower seeds are these days sold in wildflower seed mixtures, to re-create wild meadows, but since the mixtures contain much the same admix of seeds, including Tansy-Leaved Phacelia (Phacelia tanacetifolia) which is an introduced alien, re-sown wild-flower meadows look pretty much identical. You can tell it has been artificially re-created, at least initially until it gets really started with in-coming strays. Re-created wildflower meadows are purposely kept in an un-enriched state to discourage the un-restrained growth of un-welcome stray weeds (and grasses) which would otherwise choke the wanted wildflowers.

 A blue water-colour pigment can be made by mixing alum with the juice from the flowers which contains the blue pigment protocyanin.

Habitat used to be: arable fields on dry, friable soils, either calcareous or acidic, but now almost all are planted in a wildflower mix.

Just like most other members of the Daisy & Dandelion Family, the Centaurea Genus, to which Cornflower belongs, contains several sesquiterpenes and sesquiterpene lactones. Cornflower itself has been found to contain a germacranolide based sesquiterpene lactone Cnicin and some polyacetylenes and flavonoids. They also contain certain amounts of photoactive thiophenes, which are potentially toxic.

The petals are used in Tisanes (Herbal Teas) such as Lady Grey, made famous by Twinings. They are also used in salads to add a bit of colour. The Cornflower is the official flower of France.


The metalloanthocyanins are supramolecular co-pigmentation complexes with metal ions, 3-O-glycosides of anthocyanins and flavones in stoichiometric amounts and which self assemble themselves.

 The supramolecular pigment in Cornflower is called Protocyanin and has been shown to be a self-assembling stoichiometric mixture of anthocyanin, flavone, one ferric ion, two calcium ions and a magnesium atom. In Cornflower Protocyanin is deep blue in colour but in Red Roses it is red, the difference being due to difference in pH in the petals. The molecular formula is of the order of C366H384O228FeMgCa2. Protocyanin is a supramolecule composed of 6 moieties of the glycoside CentauroCyanin, 6 moieties of the glycoside MalonylFlavone plus a magnesium ion and a ferric ion.

These are the main sub-units of Protocyanin.

In CentauroCyanin, the glucoside moieties are shown in red, the Cyanidin moiety in blue, and the Succinic Acid moiety in black. There are 6 of these CentauroCyanin units in Protocyanin. CentauroCyanin is chemically:

In MalonylFlavone, the glucoside moiety, as above, is shown in red, the Malonic Acid moiety in green, the Apigenin flavone in purple and the Glucuronic Acid unit in orange. Protocyanin requires six of these MalonylFlavone units too. MalonylFlavone is chemically:

The 6 units of CentauroCyanin plus 6 units of MalonylFlavone are linked with two atoms of calcium and one each of iron and magnesium.

Glucuronic Acid is a carboxylic acid with a structure very similar to that of Glucose, but with an extra =O group. In both plants and mammals (except primates including humans) Glucuronic Acid is a pre-cursor to Ascorbic Acid (Vitamin C).

For another Metalloanthocyanin see Hydrangea.

  Centaurea cyanus  ⇐ Global Aspect ⇒ Asteraceae  

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Centaurea cyanus

Daisy & Dandelion Family [Asteraceae]

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