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)].
Easily confused with : rayed versions of Common Knapweed but especially of Lesser Knapweed (now known as Chalk Knapweed (Centaurea debeauxii)).
Easily mis-identified as : a rayed version of Lesser Knapweed(now known as Chalk Knapweed (Centaurea debeauxii)) but that has a Greek urn shaped 'head' or flower bud and leaves that have far fewer lobes, but rather with two auricles going part-way around each side of the stem.
Hybridizes with :
Brown Knapweed (Centaurea jacea) which is almost extinct in the UK to produce Hybrid Knapweed (Centaurea × gerstlaueri) which seems to be available as a garden plant, so is slightly more widespread.
Not to be confused semantically with : Knotgrasses such as Knotgrass,
Equal-leaved Knotgrass or
Northern Knotgrass which belong to the Dock & Knotweed Family, namely Polygonium [they both have similar names]. Nor should they be confused with Knotweeds such as Giant Knotweed,
Japanese Knotweed or Lesser Knotweed which also belong to the Dock & Knotweed Family (Polygonium).
The Centaurea Genus encompasses many plants with thistle-like flowers (but not thistle-like stems or leaves), many of which have 'rays' on the outer edge which consist not of ray-florets (flat 'petals') but very long tubular disc-florets that have five deep clefts at the end, much like as those in Greater Knspweed, although not all are purple. Besides the Knapweeds, these include such plants as the sky-blue Cornflower, Perennial Cornflower and others that are not rayed such as Red Star-Thistle,
Yellow Star-thistle and
Lesser Star-thistle. Mr Clive Stace thinks the genus over-crowded with disparate plants, and that this genus is ripe for splitting into other genera.
Grows in grassy places especially on lime. Sometimes it is host to a parasitic plant called Knapweed Broomrape (Orobanche elatior) which specialises in being parasitic only on Greater Knapweed which may be several metres away, but connected underground.