Common yarrow (Achillea millefolium) was one of the earliest plants I added to my butterfly garden. It definitely attracts pollinators and it showed up on several lists of best plants for my area. This spring, I even gave some to several neighbors because of my success with it. Soon after, I was forced to reconsider the whole enterprise when I saw yarrow on a list of non-native, invasive species for this region. What exactly was going on here? Did I make a mistake years ago that had perpetuated all this time? Was there some new information about this plant? What else might I be wrong about in all my dedicated efforts to plant a mostly native garden? Was my whole crusade to support biodiversity a fool’s errand?
I started researching with a lot of my go-to sources. Sure enough, some of them showed it as non-native, others as native, and still others as… both. They didn’t all agree on the scientific name, either. What? So I started using search terms like “yarrow native range” and “yarrow native distribution,” which shed very little light on the matter. Instead my search presented me with phrases like “native to the Northern hemisphere” and “cirumboreal distribution.” This was about as useful as when you’re eight and a grown-up asks you where you live, and with a mischievous grin you say: “Earth.”
Further reading started to clear this up: yes, it is native to Asia, Europe, and North America and yes that native range more or less includes all of the United States… but it’s also much more complicated. I was beginning to see how a plant could be both “native” and “introduced” to the same place, but I wasn’t quite getting it until I came across this excellent piece. Nowhere else could I find all of the pieces of the puzzle so elegantly combined. I won’t try to do the same here but essentially it is a species complex, there are many cultivars, and human interaction with the plant is extensive. Some of what we call Achillea millefolium is native, some is not, some may have characters of both the native and non-native varieties, and good luck to any non-biologists determining if an individual specimen is locally native!
The linked history with human activities makes me start thinking in circles. That interaction is over such a long time scale that it blurs the line between native and introduced. If humans aided its distribution, but over tens of thousands of years in lockstep with our own expansion, was that a natural process? This to me is an astonishingly fascinating question. It is certainly much different than one guy bringing a hundred starlings to a new continent, but is it also different from a plant gradually increasing its range as its seeds are distributed by birds? If so, just how different? Where is the line between humans as a part of nature and humans disrupting or interfering with nature? How we answer these questions can shape the very core of environmentalism, and I doubt there is one right answer.
Aside from that rabbit hole of natural philosophy, I also needed to decide if I still believed common yarrow was a good choice for my butterfly garden. Are its native or invasive characters stronger? I don’t immediately disregard all non-native plants in my landscape choices, but I do typically steer clear of anything that’s a known invasive in my area. I have noticed that this plant spreads aggressively – as predicted by every source I consulted years ago. Most of what I have planted is the white-flowering, “natural” variety and not one of the brightly-colored cultivars. It does provide the ecosystem function of attracting pollinators and it is a host plant for some local butterfly species. I can control the spread in various ways and it is hardy and low-maintenance. Is it a net benefit to the local ecosystem? I could envision a reasonable defense of either position based on my understanding of the available facts. A purist might say that with no way of knowing for certain that your plant is a locally native ecotype (or technically a native species at all) one should never include that plant in support of biodiversity. A non-purist might counter that because it serves the ecological function of a native, and some related forms are native, there’s no reason to exclude it. I believe in this case there are angels on both shoulders who happen to disagree.
For now, I am listening to the angel on the non-purist shoulder. I will be looking to replace any brightly-colored varieties with other plants, since I know for sure those are cultivars. I will keep the white-flowered specimens I have and manually restrict their spread. It hasn’t (so far) choked out any of my other plants, but there are plenty of other avenues to adding yellow and pink blooms to my garden for color balance. Fortunately, this isn’t an irreversible decision. I’m perfectly willing to reevaluate a matter this cloudy now and again. I am still building my knowledge base on Maryland native plants and as my familiarity with other species increases I may find there is no longer room for a plant that walks in both the native and invasive worlds.