You have probably driven by millions of tansies if traveling through much of the north east part of Minnesota. In fact, you have probably driven past stands of them in many US regions. In our corner of Minnesota, in August, the tansy in ditches and roadside hills is as ubiquitous as the sound of cicadas and advertisements for the Minnesota State Fair (but far less noticed than the State Fair or advertisements for it). Colloquially, they are known as golden buttons, cow bitter, bitter buttons and several likewise-goofy sounding names and like the common dandelion, the tansy is not native to this side of the Atlantic. Like a large swath of the US population, tansies can be traced back to Europe (and Asia).
Like the Irish, at one time in the United States, the tansy is considered to be a nuisance. Here in Minnesota, the Department of Agriculture lists it as a "bad plant" This basically means there is no net positive economic benefit from this plant. If you could make flour from it, or it cured herpes, there would be fields of cultivated tansies throughout the upper midwest and many other places. But, it is not magic and does not produce flour. It has been found, however, to be a viable deterrent for the Colorado potato beetle. We actually left the wild stands of tansies around the potatoes this year; anecdotally, things turned out very well. It is looking to be a good potato-year.
It still does not leave much love for the lowly tansy, though. I think Ralph Waldo Emerson summed things up nicely; "What is a weed? [It is just] a plant whose virtues have not yet been discovered."