C. cyanus formerly occurred as an annual weed of arable habitats. Since 1986 it has been recorded in very few arable fields, but it is now frequent in waste places, on roadsides and on rubbish tips as a casual arising from gardens and wild-flower seed mixtures. 0-350 m (Blackwell, Derbys.).
Known to have been present in Britain from the Iron Age onwards, C. cyanus remained a serious weed until seed cleaning began a rapid decline, accelerated by the use of herbicides. Since the 1980s it has increased through wild-flower seed.
As an archaeophyte C. cyanus has a distribution centred on the European Temperate region; it has been widely naturalised outside this range.
Light (Ellenberg): 7
Moisture (Ellenberg): 5
Reaction (Ellenberg): 6
Nitrogen (Ellenberg): 5
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 3.8
July Mean Temperature (Celsius): 15.4
Annual Precipitation (mm): 836
Height (cm): 80
Perennation - primary
Life Form - primary
Clonality - primary
Count of 10km squares in Great Britain: 884
Count of 10km squares in Ireland: 56
Count of 10km squares in the Channel Isles: 5
Atlas Change Index: -0.39
Weighted Changed Factor: 62
Weighted Change Factor Confidence (90%)
Plantatt Conservation Status
RDB Species Accounts
Centaurea cyanus L. (Asteraceae)
Cornflower, Penlas Yr d
Status in Britain: ENDANGERED.
Status in Europe: Not threatened.
C. cyanus is a plant of arable habitats, chiefly but not exclusively on sandy loam soils, and in the past was a troublesome weed. It was formerly widespread in Britain, especially in the south and east, but in recent decades has shown one of the most rapid declines of any plant in the British flora. It was known from about 264 hectads between 1930 and 1960, from fewer than a hundred between 1960 and 1975, and fewer than 50 between 1976 and 1985 (Smith 1986). Since 1986, C. cyanus has been recorded in very few arable fields, although it has occasionally appeared as a non-persistent casual on excavated soil in former arable land. Many of the recent occurrences on road verges can be attributed to the increasing use of 'wild flower' seed, probably of continental origin, and most of the mapped records may be of such origin.
C. cyanus is an annual, flowering between June and August. It is self-incompatible, and is cross-pollinated especially by flies and bees. It is thought to be largely autumn-germinating and is associated with autumn-sown crops, although some seed can also germinate in the spring. There is evidence that most seed remains viable in the soil for up to four years (Svensson & Wigren 1986), though the occasional appearance of plants on old sites suggests that a small proportion may remain viable for much longer. Seed can be produced by early July by autumn-germinated plants. The seeds are relatively heavy for an annual species and tend to remain close to where the parent plant grew. In common with many other species of arable plant, C. cyanus is not a highly mobile, ephemeral species, but rather is restricted to areas where there has been long continuity of arable farming.
There are recent records from arable fields in Wiltshire, the Isle of Wight, Buckinghamshire, Lincolnshire and Suffolk, but it is believed that the last county supports the sole remaining arable field population in Britain which is persistent and self-sustaining. It is associated there with a typical flora of sandy arable fields, including Anchusa arvensis, Anthriscus caucalis and Papaver argemone.
Changes in arable practice have caused the decline of this once well-known and common species. It is possible that improved methods of seed cleaning introduced at the end of the 19th century eliminated the seeds from seed-corn. It is thought to be susceptible to a wide range of herbicides, and this combined with the mainly rather short-lived seed are probably the main reasons for its rapid decline. The Suffolk site is currently part of a conventionally farmed arable field, and research continues there to determine the ideal conservation management. This species is regarded as critically endangered in Britain because of the extreme restriction of persistent populations.
It is distributed throughout Europe and many of the other cereal-growing parts of the world. In common with many other species it has become much less frequent in parts of northern Europe where arable farming has become more intensive, and in a few other areas it is as threatened as in Britain.
P. J. Wilson
Scarce Atlas Account
Centaurea cyanus L.
This plant was formerly a weed of arable land, particularly on sandy, rather acidic soils where it was associated with Chrysanthemum segetum. C. cyanus used to grow mainly in crops of rye, but it could occur in other spring and winter crops and as a ruderal, provided competition from other plants was slight. In the eighteenth and nineteenth centuries, it constituted a serious agricultural weed and possibly maintained its population with continuous reintroductions in rye seed from eastern Europe and Russia. Now it is more often seen as a cultivar in gardens or where ‘wild flower seed’ has been sown.
C. cyanus is an annual. There are peaks of germination in September/October and May/June. The flowers open in long days and are self-incompatible. They are cross-pollinated by bumble bees. Fruits are relatively large and heavy and can be harvested with the grain. Although germination is greatest in the first year after sowing, viability can be retained for at least 4 years (Svensson & Wigren, 1985). This enables it to survive crop rotations as long as perennial leys are not included and the competition pressure is not too high. It occasionally overwinters.
This species has the potential to occur on suitable sites throughout Britain, and the poet John Clare referred to its "destroying beauty". The species declined rapidly with the introduction of seed screening and, later, with the advent of chemical herbicides such as 2,4-D and MCPA. This species is now known from only one persistent site in Britain, in mid-Suffolk. Isolated plants still occur over a large area of the south and east of England although these rarely persist for longer than a year. Large numbers sometimes occur when there are deep excavations for roads and pipelines. Although there are records from 127 British 10 km squares from 1970 onwards, this declining species is classified as scarce as it has been recorded in only 78 British 10 km squares from 1980 onwards.
This species is thought to have originated in southeast Europe but it has spread with agriculture and is now widespread in both the northern and southern hemispheres.
Godwin (1975) suggests that this species once grew in natural communities on scree slopes and alluvial deposits of the late-glacial tundra.
Atlas text references
1988. The Irish Red Data Book. 1. Vascular Plants.
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
1992. Vergleichende Chorologie der zentraleuropäischen Flora. Volume 3. 2 vols.
1994. Scarce plants in Britain.
1999. British Red Data Books. 1. Vascular plants, edn 3.