Flora of Door County, Wisconsin

As of 2019, 1201 species and hybrids of vascular plants have been identified in the county,[1] including the yellow lady's-slipper Cypripedium parviflorum, the official county flower.[2] 255 unique taxa of mosses, liverworts, and hornworts[3] have been identified in Door County.

Along with nearby Marinette and Delta (see Garden Peninsula) counties, Door County is home to endemic plants and disjunct populations,[9] such as those protected at Plum Island, Coffee Swamp, Cave Point County Park, the adjacent Whitefish Dunes State Park, and The Ridges Sanctuary. The Grand Traverse islands have some of Wisconsin's richest rare plant reserves.[10]

In 2019, 25 miles of roadsides were surveyed for invasive species.[11] A county-wide electronic map of Japanese knotweed, Phragmites, teasel, and wild parsnip infested locations is updated annually.[12] Locations of other problem species have also been documented.[13]

The county is home to a variety of plant communities, including some unique to the area. Boreal rich fen is called "rich" because the dolomite makes the soil more fertile.[14] Calcicole plants growing in these fens depend on minerals which the dolomite contributes to the soil.[15] The southernmost boreal forests in the state are on the eastern side of the peninsula.[16] In white cedar variant forests, white cedar coexists with hardwoods and balsam fir in upland stands that ordinarily would not support cedar. This forest cover is likely due to the alkaline soil and mostly grows on the Niagara Escarpment along the Green Bay side of the peninsula or near the Lake Michigan shoreline. A combination of high humidity, high levels of calcium and magnesium carbonates from the dolomite, and weathered, nutrient poor soils are thought to limit microbial activity. As a result, a layer of humus builds up from organic matter falling to the ground.[17] The escarpment also features the dry cliff natural community[18] and is home to two rare species of whitlow grass.[19][20] Other uncommon communities are alvar and the similar Great Lakes alkaline rockshore,[21][22] also home to rare plants.[9]

Plants in Newport State Park recolonizing the drawdown zone in August 2013 during a period of low lake levels. Plants present in the background include Anthriscus sylvestris (Queen Anne's lace), goldenrod, Cirsium arvense (Canada thistle), and Phalaris arundinacea (reed canary grass). The foreground includes the woody plants Thuja occidentalis (white cedar), and Cornus sericea (red-osier dogwood).

Yearly fluctuations in lake levels alternately kill off vegetation during periods of high water and promote succession during times of low water. Even during times of high water when low-lying plants are inundated, the populations may persist uphill by clonal expansion and spreading their seeds. Lake Michigan has more diverse shoreline vegetation than Lake Ontario, which has a more stable water level due to human intervention. Without the changing lake levels the shoreline would be dominated by woody plants or highly competitive and even invasive water-loving species such as cattails, reed canary grass, or purple loosestrife. Wet meadows like this one thrive when flooding does not occur often enough to allow emergent vegetation to prevail but is still too frequent to allow the establishment of trees and shrubs.[23]

Some trees have attracted attention:

• One white cedar found on the escarpment was over 600 years old and near other old-growth cedars.[24]
• The largest tree in the county is a 170-year-old eastern cottonwood on the west side of Highway 57 passing through Institute. It is 110 feet tall and 35 feet in circumference.[25]
• In 1997, striped maple was discovered in a shoreline forest near Newport, the first time this species was documented in the state.[26]
• In 1969, Franklin Gilbert introduced the Viking apple, an early Macintosh moderately resistant to apple scab and fireblight.[27][28] The original Viking tree is exhibited to the public at the Peninsular Research Station.

As of 2019, 243 species of mushrooms and other macrofungi have been identified north of the canal,[29] with 326 species for the county as a whole, including those found in lichens.[30] Several of the more uncommon lichens found in the county are Cetraria arenaria, which grows on the ground,[31] and Anaptychia crinalis, which grows on tree bark.[32]

In 2009, a unique hybrid of Saccharomyces cerevisiae yeast was found on fallen cherries near Fish Creek. This strain of S. cerevisiae descended from both oak-tree and vineyard lineages.[33]

• Flora of the United States

• Wildflowers of Door County: Wisconsin's Unique Floral Preserve by Paul G. Mahlberg and Marilyn Waite Mahlberg, Bloomington and Indianapolis, Indiana: Indiana University Press, 2000
• Door County's Wildflowers: A Field Guide for the Curious by Frances M. Burton and Aurelia M. Stampp, Ephraim, Wisconsin: Stonehill Publishing, 2005
• Door County Flora: A Field Guide to the Vascular Plants of Wisconsin's Door Peninsula by Steve W. Chadde, Sullivan, Indiana: Orchard Innovations, 2020
• The Flora of the Limestone Cliffs and Terraces of Door County, Wisconsin by Grace Jean Baird, Chicago: University of Chicago, 1919
• Biodiversity of Macrofungi in Northern Door County, WI by Charlotte Lukes, Cofrin Center for Biodiversity, UW-Green Bay,