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U.S. Forest Service

Plant of the Week

Map of the United States showing states. States are colored green where dwarf lake iris may be found. Range map of dwarf lake iris. States are colored green where the species may be found.

dwarf lake iris flowers. Dwarf lake iris (Iris lacustris). Photo by Linda Swartz.

Cobble beach habitat on Lake Michigan. Cobble beach habitat on Lake Michigan.

Dwarf Lake Iris (Iris lacustris Nutt.)

By Wayne Owen

This is a rare and stunning find! The vivid blue, showy flowers (about two inches in height) of Dwarf lake iris are truly exquisite. This miniature iris, honored as the state flower of Michigan, blooms from mid May to early June.

Dwarf lake iris is called a Great Lakes endemic due to its very limited range. It inhabits the northern shores of Lakes Huron and Michigan within Michigan, Wisconsin (Door Co.), and Ontario, Canada (Manitoulin Island, and the Bruce Peninsula). Dwarf lake iris formerly ranged as far south as Milwaukee, Wisconsin, but has never collected on Lake Superior shoreline.

The Latin species name lacustris translates to "of lakes", which does not speak to the immense size of these two huge inland "seas". Confined almost exclusively to thin soil over limestone, rich gravel or bedrock, or moist sands and gravels, it can persist in full sunlight on moist sites. This miniature iris is most successful, however, under the light, dappled shade of white cedar. It flowers best in semi-open habitats such as the long and narrow strips of land bordering the high-water line, or large flat expanses behind open dunes. It may also inhabitant old beach ridges of the former shores of these two Great Lakes. The changing water levels of lakes Michigan and Huron serve to create new habitat.

Thomas Nuttall, renowned naturalist and explorer, first found this species in 1810. The type locality, or location where he first found Dwarf lake iris, was Mackinac Island in northern Lake Michigan.

Growth habitat can be described as a low growing perennial with shallow, slender, creeping rhizomes; large stands may represent a few clones.

Dwarf lake iris was listed as federally threatened in 1988, is state threatened in MI, and endangered in Wisconsin. Habitat has been greatly reduced by shoreline development for residential or vacation homes, road widening, chemical spraying and salting, and disturbance and destruction by off-highway vehicles. Iris lacustris has been known to be offered for sale commercially; collection from wild populations may negatively affect this species and may be in violation of State or Federal laws.

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