Sneezewort (Achillea ptarmica)
This time of year, riversides and wet meadoes are good places to look for flowers a bit out of the ordinary and that is where you find Sneezewort.
Sneezewort is described as being 'local' and so where it occurs it is usually quite common but finding places where it occurs is a bit more difficult. Certainly, the lower reaches of the River Frome is one place. It has a preference for acid soil rather than chalk so it is unlikely to be found further up stream in the chalk areas where our streams tend to originate.
Flowering in July and August you can find it now on Wareham Common. I have no idea why it is called Sneezewort but I suspect it has connections to the Great Plague!