Spotted Knapweed (Centaurea maculosa)
A close relative of the garden Bachelor’s Button (Centaurea cyanus), this is a European import found especially along railroad tracks; this one was by a disused siding in Oakmont. The color is variable from purple through white.
From Gray’s Manual: C. MACULOSA Lam. Pubescent or glabrate, with ascending rather wiry branches; involucre ovoid-cainpanulate, in fruit becoming open-campanulate; the outer and middle ovate bracts with rather firm points and with 5-7 pairs of cilia at the dark tip; innermost bracts elongate, entire or lacerate; corollas whitish, rose-pink, or purplish, the marginal falsely radiate. Waste places, roadsides, etc., N. E. to N. J.
(Adv. from Eu.)