The coastal Great Lakes alvar habitats are covered by thin layers of soil or consist of bare limestone rock. These are some of the world’s most beautiful natural rock gardens, with unique plants such as the lakeside daisy (Hymenoxys acaulis), ram’s head ladyslipper (Cypripedium arietinum), and dwarf lake iris (Iris lacustis), Michigan’s state wildflower.

To survive, plants on these alvar habitats must be tough, tolerant of wet conditions in the spring followed by extreme heat and drought later in summer. Lichens and moss abound on the rocky surfaces, and plants are often confined to the fissures or “strikes” between slabs of limestone. Trees and shrubs are often stunted, pruned back by both wind and drought. The alvar Coastal Garden showcases some of the most distinctive plants in this zone.

At times, the alvar known as limestone pavement is covered with a thin layer of mineral soil and supports a calcareous grassland. These places are home to a number of rare plants and animals more commonly found in prairie grasslands. One of the best examples of this habitat is found on Drummond Island, Michigan and is known as the Maxton Plains. Here on the 400 million-year-old bedrock grow grasses such as prairie dropseed (Sporobolis heterolepis) together with broadleaved forbs such as prairie smoke (Geumtriflorum), early buttercup (Ranunculus fascicularis) and early saxifrage (Saxifraga virginiensis). A portion of our Coastal Garden will simulate this unique grassland alvar habitat.

In many places around the Great Lakes, the wave-action together with freezing and thawing of limestone bedrock have created beaches of varying thicknesses of limestone cobble. These are often on the scenic headlands where lighthouses still stand as sentinels. Common vegetation on these beaches may include harebell (Campanula rotundifolia), sedges (Carex eburnean), Indian paintbrush (Castilleja coccinea), fringed gentian (Gentianopsis procera), and silverweed (Potentilla anserina). Noteworthy woody plants include paper birch (Betula papyrifera), balsam poplar (Populus balsamifera) and northern white cedar (Thuja occidentalis).

Many people associate the broad sand and gravel beaches and the majestic dunes of Saugatuck, Sleeping Bear, and others with vacations along the Great Lakes. These popular places host unique flora featured in our Great Lakes Garden, including the endemic Pitcher’s thistle (Cirsiumpitcheri) and Lake Huron tansy (Tanacetum huronense). Other characteristic plants include marramgrass (Ammophila brevigulata), wild wormwood (Artemesia campestris), sand reed grass (Calimovilfa longifolia), sand cherry (Prunus pumila), starry false Solomon’s seal (Smilacina stellata), and various willows (Salix spp.) and grasses.