Rolfsmeier discussed several historic or relict plants as well as those that appear far from their natural range, known as disjunct populations.
He said his interest in biogeography goes back about 15 years. This branch of botany contributed to the concept of continental drift based on plant species patterns and is referred to as "the queen of outdoor botany" by professionals in the field.
Rolfsmeier discussed several possible reasons for relict and disjunct species.
One explanation is that, in spite of general climate changes, the plant is able to survive and thrive in isolated habitats where the local climate is similar to that of their main range.
Drainages can also provide a corridor for plants to migrate from one isolated area of suitable habitat to another. For example, what is now called the Platte River followed a route to Kansas during the glacial period, creating disjunct plant populations.
Another is introduction by animals known as “dirty ducks’ feet dispersal,” or by humans who intentionally or unintentionally cultivate a plant out of its natural range.
“The Buckeye tree in Sioux County appears to have been introduced by humans but then escaped cultivation and seems to be thriving on its own,” he said.
He emphasized that dots on maps representing certain species can be skewed because more plants are collected in areas where large numbers of botanists live.
“A gap on the map doesn’t mean the plant doesn’t live there. Absence of evidence is not evidence of absence,” he said.
The presentation focused on the Sandhills, a 20,000 square mile area, which features 600 native plant species, an unusually high level of biodiversity compared to other sand dune regions worldwide.
Rolfsmeier discussed wetlands permanently saturated with groundwater and organic soils, known as fens. One fen in Cherry County is 22 feet deep and about 70 percent of the material in it includes spruce pollen, typically a far northern species. Also, far northern wildflower species can still be found in the Sandhills.
Rolfsmeier has participated in several surveys of far northern relicts including one in Holt County in 1987 with his college adviser. Rolfsmeier collected a sample of Gattinger's gerardia but initially questioned the possibility of a disjunct relict until he received confirmation from an expert.
In 2011 near Atkinson, Nebraska, Rolfsmeier found an extremely small, carnivorous bladderwort. This was a significant discovery because it is a Gulf Coastal species growing far out of its main range.
“I keyed it in half a dozen times to be sure I was right,” Rolfsmeier said. An expert verified Rolfsmeier’s discovery of zigzag bladderwort.
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