A Comparative Biogeography of the Vascular Floras of Illinois and Indiana

Abstract

A symposium on c biodiversity and the natural history collections of Illinois and Indiana was held at the 2017 annual meeting of the Indiana Academy of Science and included an analysis of the biogeography of the vascular plant floras of these two states. The analysis documented a rich temperate zone flora: the species shared by the two states numbered 2540 and a total count of 3450 species (native and nonnative). Although the two states have much in common physiographically, on a per log10 km2 basis Illinois possesses the richer flora. Illinois has at least 360 native species in its flora that do not occur in Indiana while only 165 species are limited to Indiana. The richer Illinois flora was due to a larger influence by the Great Plains flora, larger numbers of species reaching their northern limit in the Mississippi Embayment, more species reaching their southern limits especially within the Driftless Area of Illinois, and elements of the Ozark flora reaching into southern and western Illinois. Furthermore, at least 58 species introduced into Illinois (but not into Indiana) have a nativity from western US. Although Indiana has a notable Appalachian component in its flora, these deciduous forest species tend to also be found in the southern Illinois hill country. However, unique to Indiana was a suite of coastal plain disjunct species with populations in northwestern Indiana and also southwestern Michigan.