I am stumped. Without a photo of leaves, as opposed to the bracts under the flower clusters in your photos, and a photo of a whole plant, I cannot ID this plant. Betty
BettyDonWood MichaelMulvaney - thanks, the 4 petal versions of the common centaury were found in close proximity to 5 petal versions (the 4 petal versions making up 20% of the number). They were quite distinct: smaller, carrying fewer flowers, with ragged basal leaves.
A few of our other sightings have what look like 4 petal flowers amongst predominately five petaled one see Centaurium erythraea (Common Centaury) on 13 Dec 2015