If one recognizes two distinct varieties of buttonbush, Cephalanthus occidentalis var. occidentalis has a distribution range that spans much of eastern North America. The other variety, Cephalanthus occidentalis var. californicus, is native to southwest North America and south into Central America. Treated as one combined taxon instead of two distinct varieties, as is done by the USDA PLANTS database, this becomes a rather remarkable species — a woody plant with a distribution range that spans from Canada into the tropics.
In most cases, if asked, I’d say that species with wide distribution ranges are tolerant of a broad suite of environmental conditions. In this case, though, I suspect it primarily (though not exclusively) has to do with having some consistency in habitat across its range; it is a species of wetlands and forested swamps.
The Missouri Plants web site has additional images of Cephalanthus occidentalis. For those of you who are gardeners, you should investigate the Kemper Center for Home Gardening’s page on buttonbush (it is ranked as a Plant of Merit).
As for the lepidopterans in today’s photographs, the first photograph features an eastern tiger swallowtail. I don’t know the identity of the second butterfly, so I’ll leave that up to one of you (thank you!).