We have been watching this thistle plant, while removing the other "field" thistles from the wetland area. Probably 'Musk Thistle'
Carduus nutans, or ‘Plumeless Thistle’
Carduus acanthoides, the seed germinated last summer. It over wintered as a rosette protected by leaf litter and a cover of snow.
We noticed this rosette among the ground clutter after the snow melted. Through May, it resumed vegetative growth. It is growing tall now, and branching out to produce numerous large flower heads.
This particular plant is just a lot of green now, hiding among more green.
But when it finally blossoms, you will not be able to miss the deep purple magenta flowers!
After blooming and setting seed the whole plant will die, thereby completing the life cycle.
But this plant can produce 120,000 seeds that could germinate this season and form little rosettes to wait out winter. Rather than allow this species to spread and become a nuisance in the pond area, DNR recommends control before flowering. We will enjoy the beginning of flowering and try to cut off development of any seeds.