Special flora and vegetation of Indiana Dunes National Park
Authors: Pavlovic Noel , Plampin Barbara , Tonkovich Gayle , Hamilla David 
Published: February 2024

The Indiana Dunes (comprised of 15 geographic units (see Figure 1) which include Indiana Dunes National Park, Dunes State Park, and adjacent Shirley Heinze Land Trust properties) are remarkable in the Midwest and Great Lakes region for the vascular plant diversity, with an astounding 1,212 native plant species in an area of approximately 16,000 acres! This high plant diversity is the result of the interactions among postglacial migrations, the variety of soil substrates, moisture conditions, topography, successional gradients, ?re regimes, proximity to Lake Michigan, and light levels. This richness is all the more signi?cant given the past human alterations of the landscape resulting from logging; conversion to agriculture; construction of transportation corridors, industrial sites, and residential communities; ?re suppression; land abandonment; and exotic species invasions. Despite these impacts, multiple natural areas supporting native vegetation persist. Thus, each of the 15 units of the Indiana Dunes presents up to eight subunits varying in human disturbance and consequently in ?oristic richness. Of the most signi?cant units of the park in terms of number of native species, Cowles Dunes and the Dunes State Park stand out from all the other units, with 786 and 686 native species, respectively. The next highest ranked units for numbers of native species include Keiser (630), Furnessville (574), Miller Woods (551), and Hoosier Prairie (542). The unit with lowest plant richness is Heron Rookery (220), with increasing richness in progression from Calumet Prairie (320), Hobart Prairie Grove (368), to Pinhook Bog (380).

Signi?cant natural areas, retaining native vegetation composition and structure, include Cowles Bog (Cowles Dunes Unit), Howes Prairie (Cowles Dunes), Dunes Nature Preserve (Dunes State Park), Dunes Prairie Nature Preserve (Dunes State Park), Pinhook Bog, Furnessville Woods (Furnessville), Miller Woods, Inland Marsh, and Mnoke Prairie (Bailly).

Wilhelm (1990) recorded a total of 1,131 native plant species for the ?ora of the Indiana Dunes. This was similar to the 1,132 species recorded by the National Park Service (2014) for the Indiana Dunes. Based on the nomenclature of Swink and Wilhelm (1994), Indiana Dunes National Park has 1,206 native plant species. If we include native varieties and hybrids, the total increases to 1,244 taxa. Based on the nomenclature used for this report?the Flora of North America (FNA 2022), and the Integrated Taxonomic Information System (ITIS 2022)?Indiana Dunes National Park houses 1,206 native vascular plant species.

As of this writing (2020), the Indiana Dunes is home to 37% of the species of conservation concern in Indiana (241 out of 624 Indiana-listed species): state extirpated = 10 species, state endangered = 75, and state threatened = 100. Thus, 4% of the state-listed species in the Indiana Dunes are extirpated, 31% endangered, and 41% threatened. Watch list and rare categories have been eliminated.

Twenty-nine species once documented from the Indiana Dunes may be extirpated because they have not been seen since 2001. Eleven have not been seen since 1930 and 15 since 1978. If we exclude these species, then there would be a total of 1,183 species native to the Indiana Dunes. Many of these are cryptic in their life history or diminutive, and thus are di?cult to ?nd.

Looking at the growth form of native plants, <1% (nine species) are clubmosses, 3% (37) are ferns, 8% (297) are grasses and sedges, 56% (682) are forbs or herbs, 1% (16) are herbaceous vines, <1% (7) are subshrubs
(woody plants of herbaceous stature), 5% (60) are shrubs, 1% (11) are lianas (woody vines), and 8% (93) are trees.
Of the 332 exotic species (species introduced from outside North America), 65% (219 species) are forbs such as garlic mustard (Alliaria petiolata), 15% (50 species) are graminoids such as phragmites (Phragmites australis ssp. australis), 2% (seven species) are vines such as ?eld bindweed (Convulvulus arvensis), <1% (two species) are subshrubs such as Japanese pachysandra (Pachysandra terminalis), 8% (28 species) are shrubs such as Asian bush honeysuckle (Lonicera spp.), 1% (three species) are lianas such as oriental bittersweet (Celastrus orbiculatus), and 8% (23 species) are trees such as tree of heaven (Ailanthus altissimus).

Of the 85 adventive species, native species that have invaded from elsewhere in North America, 14% (11 species) are graminoids such as broom sedge (Andropogon virginicus), 57% (48 species) are forbs such as fall phlox (Phlox paniculata), 5% (six species) are shrubs such as Carolina allspice (Calycanthus floridus), 3% (two species) are subshrubs such as holly leaved barberry (Berberis repens), 1% (one species) is a liana (trumpet creeper (Campsis radicans), 3% two species) are herbaceous vines such as tall morning glory (Ipomoea purpurea), and 17% (15 species) are trees such as American holly (Ilex opaca).

A total of 436 species were found to be ?special? based on political rankings (federal and state-listed threatened and endangered species), species with charismatic ?owers, and those that are locally rare.