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DNA Confirms 3 Plant Species New to Arkansas; 1 New to Science

Arkansas Natural Heritage Commission - Friday, December 15, 2017

New discoveries are often made because something doesn’t look quite right. This is especially true in biology.

“When we’re in the field we always look for odd-looking specimens that don’t quite fit what we’re used to seeing,” ANHC Botanist and Ecologist Theo Witsell said.

This year ANHC field volunteer Jim Keesling made a number of collections of odd-looking specimens in the genus Eupatorium, a large and complex group of plants in the sunflower family (Asteraceae) commonly known as the bonesets or thoroughworts. These were added to a stack of other “problem specimens” of Eupatorium that Witsell has gathered over the last several years.

Eupatorium is a “high action” genus according to Witsell, with a lot of genetic complexity resulting from hybridization, polyploidy (having multiple sets of chromosomes), and apomixis (the interesting ability to reproduce asexually from seed - making genetic copies of the parent plant). This occasionally allows what would normally be a one-time sterile hybrid between two different species to become self-sustaining and capable of reproducing from seed to create entire populations. It also makes for occasional specimens that don’t conform to the published references on the genus – ones that don’t look quite right.

To help make sense of the variation they were seeing in Eupatorium in the field, Witsell and Keesling began corresponding with and sending photos to the top authority on the genus: Dr. Edward Schilling, professor of Plant Systematics at the University of Tennessee (UT) Knoxville. Schilling has conducted extensive research into the genus and has developed techniques to analyze DNA samples and determine the identity of species, determine if a specimen is a hybrid, and even identify what parent species were involved in creating a hybrid plant.

“He offered to run some analyses for us so we sent him leaf tissue from a dozen herbarium specimens that we suspected might represent species or hybrids not previously documented from Arkansas,” Witsell said.

Schilling, with the help of UT undergraduate students Magen Poindexter and Mayuri Jagadish, ran the samples and recently sent back confirmation of three species new to Arkansas, and one hybrid never before documented anywhere!

Range map showing previously known range of Eupatorium mohrii (light green counties). Courtesy of Biota of North America Project (BONAP. org)Two specimens Keesling collected this fall in the Coastal Plain (Calhoun and Ouachita counties) were confirmed to be Mohr’s thoroughwort (Eupatorium mohrii), a species previously known to occur only in southern Louisiana, adjacent Texas, and in states east of the Mississippi River (range map at direct left). Two others he collected were found to be the hybrid between Mohr’s and another species found in southern Arkansas, lanceleaf thoroughwort (E. lancifolium). This hybrid had not been previously documented anywhere.


Range map showing previously known range of Eupatorium vaseyi (light green and yellow counties). Courtesy of Biota of North America Project ( specimen Witsell collected in 2011 from a dry, gravelly ridge in the Scatter Creek Wildlife Management Area in Greene County was determined to be Vasey’s boneset (Eupatorium vaseyi) and is the first record of this species west of the Mississippi River (range map at left). Another specimen he collected in 2010 from Gulf Mountain Wildlife Management Area in Van Buren County was determined to be Torrey’s thoroughwort (Eupatorium torreyanum). This species was known to occur in Arkansas by Schilling, but its occurrence in the state was previously unknown to Arkansas botanists.

Traditionally, Arkansas botanists have recognized 10 Eupatorium species and two hybrids as being in the state. Earlier work by Schilling added two more species to this list from the Gulf Coastal Plain of southern Arkansas, and this last round of DNA work he did has now added three more species and another hybrid to the tally of state’s flora kept by the ANHC.

There are more odd Eupatorium specimens remaining at the ANHC to be studied and Keesling and Witsell have plans to continue field work on the genus in 2018 and beyond, working with Schilling to determine what is going on genetically. Watch here for updates!

Photo captions:

Top right -- Specimen of Vasey's boneset (Eupatorium vaseyi) collected by Theo Witsell from the Scatter Creek Wildlife Management Area on Crowley's Ridge in Greene County.

Top left -- Mohr's thoroughwort (Eupatorium mohrii) growing in Calhoun County. Photos by Jim Keesling.

Middle images --

Top: Map showing previously known range of Eupatorium mohri (light green counties). Courtesy of Biota of North America Project ( 

Bottom: Map showing previously known range of Eupatorium vaseyi (light green and yellow counties). Courtesy of Biota of North America Project (



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