Department of Biology

A new entry has been added to the list of plant species known to occur in Indiana: Caulophyllum giganteum, commonly known as giant blue cohosh.

Spring wildflower enthusiasts throughout Indiana are familiar with its smaller and later blooming relative the common blue cohosh, C. thalictroides. Giant blue cohosh was previously thought to be restricted to the northeastern states and southeastern Canada.

As reported in the Indiana Native Plant and Wildflower Society (INPAWS) Journal (volume 25, issue 1), member Kimberly Miser and her mother Susie Watson were hiking last spring in Robb Hidden Canyon in Steuben County, which shares a border with both Michigan and Ohio, when they encountered a species they were unable to identify. Consultation with Indiana Department of Natural Resources State Botanist Michael Homoya and assistance provided by INPAWS member Kate Sanders provided photographs and measurements that suggested the plant was C. giganteum, but no specimen was collected to document the discovery.

Photographs and field-measurements provide preliminary evidence, but specimens are the ‘gold standard’ of botanical research because the details can be examined microscopically.

Working separately on April 6, 2018, in Martin State Forest in southwestern Indiana’s Martin County, IU botanist Daniel Layton made the same discovery. Fortunately, he had the DNR-issued permit needed to collect a specimen.

Layton sought confirmation from Paul Rothrock, associate curator of the Indiana University Herbarium.

Rothrock compared Layton’s specimen with the herbarium’s 68 specimens of C. thalictroides (of which 58 are from Indiana), consulted the published literature, and concluded that the specimen was indeed C. giganteum.

Charles Deam, the first state forester for the state of Indiana, included county outline maps of all Indiana species known at the time in his book Flora of Indiana (1940). The discovery of giant blue cohosh stimulated statewide interest in adding to the county distribution records that Deam and his wife Stella were able to compile during their 35 years of fieldwork throughout Indiana. These new county distribution records were published as annual supplements in the Proceedings of the Indiana Academy of Science.

The discovery of the giant blue cohosh highlights the importance of continuous monitoring of natural resources. As changing climate and other factors affect species distribution, both citizen scientists and professional biologists have important contributions to make in keeping track of our native flora and fauna.

Established in 1885, the IU Herbarium contains about 155,000 plant specimens, including the personal collection of Charles Deam. A complete list of Indiana's flora is documented on the Consortium of Midwest Herbaria website.