Plant life within and adjacent to the Lakeshore is varied. Upland forests of beech, hemlock, and maple are found on well drained sandy soils.
Wetland soils that have developed since the retreat of the most recent glacial recession give rise to spruce, tamarack, alder, and white cedar communities. Streams and lakes are ringed with alder and striped maple. The Grand Sable Dunes are a rare collection of habitats with jack pine pockets, willow, the federally threatened Pitcher’s thistle (Cirsium pitcheri), Lake Huron tansy (Tanacetum huronense), and several species of grape ferns, including four state threatened species of Botrychium.
Aquatic macrophytes and those that are emergent from the water surface provide habitat for algae, protozoa, invertebrates, and fish. There are 76 plants that are generally categorized as aquatic in the park’s waters. The smallest plants of Pictured Rocks National Lakeshore include hundreds of taxa of algae including dinoflagellates (Pyrrhophyta), yellow-brown algae (Chrysophyta), diatoms (Bacillariophyta), and green algae (Chlorophyta). Seasonal fluctuations occur in the relative densities of these unicellular plants.
Dominant diatoms include Asterionella formosa, Fragillaria intermedia, Aulocoseira islandica, and Tabellaria fenestrate. The filamentous green alga, Bulbochaete sp., is found attached to submerged logs in softwater Legion Lake. Diatoms of this acidic lake are typically benthic, and, due to limited dissolved silica, the cells walls are not preserved in the sediments. Shapely desmids (Chlorophyta) also occupy this lake.