Knapweed vs Bachelor Button in Winter Condition

Knapweed in winter condition

Here is a plant in my garden that looks similar to my bachelor buttons.  I don't know but I suspect it is spotted knapweed (Centaurea maculosa).  It is bigger than usual and does not have the silvery look to it.  The leaves, though, look exactly the same.  I wonder if it is a different variety of Bachelor Button.  Knapweed puts out toxins that deprive other plants around it of nutrients.  Two of these plants are growing in my iris seed bed and so they must go.  The other one I may let flower and pull it before it goes to seed just to see its flower in hopes for a positive ID.