His interest in the genus Antennaria was inspired by noted evolutionary botanist George Ledyard Stebbins (1906–2000) who was a visiting professor at the Ohio State University in 1978–1979.

His early academic career was as an Assistant Professor of Biology and Curator of the Benedict Herbarium (WOCB) at University of Windsor, Ontario (1984–1987).

In 1997, he emigrated to Canberra, Australia, where he became a senior principal research scientist with the CSIRO, Division of Plant Industry working at the Australian National Herbarium (CANB).

Bayer also has expertise in taxonomy and molecular phylogeny of Citrus (Rutaceae) and its close relatives, which have great diversity in southeast Asia.

He has collected plants around the world, including Australia, New Zealand, New Caledonia, United States, Canada, South America, southern Africa, Madagascar and western Europe.