The results of a rare plant, floristic, and plant community survey of the Grand Traverse Islands archipelago are presented. Stretching from Wisconsin's Door Peninsula to Michigan's Garden Peninsula, these Lake Michigan and Green Bay islands are largely underlain by Silurian dolomite that outcrops along shorelines as high, white cedar-dominated cliffs (on west coasts), low wave-washed shelves (east coasts), and, occasionally, interior escarpments. Most islands experienced intensive human use in the 19~th century (fishing, concomitant logging and farming) but have now recovered to second- and third-growth forests. An exception is Washington Island, the largest in the archipelago, which has a permanent human population and much cultivated or formerly cultivated land. Islands larger than about 100 ha have interiors dominated by beech (Fagus grandifolia)—sugar maple (Acer saccharum) forests that may have rich spring ephemeral displays, including, on Washington and Rock Islands, the rare disjunct broad-leaved wood sedge (Carex platyphylla). These mesic forests are best developed on the western and northern sides of islands, where glacial till overlies dolomite. The eastern shores often have boreal conifer-dominated beach ridge and swale complexes (best developed at Jackson Harbor on Washington Island) with regional endemic calciphiles such as dwarf lake iris (Iris lacustris) and boreal disjuncts like northern comandra (Geocaulon lividum). Small dune complexes may have regional endemics such as Pitcher's thistle (Cirsium pitcheri) and Lake Huron tansy (Tanacetum huronense), but these appear to be declining due to intensive human use of Great Lakes beaches.
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