Inference of Ploidy Level in 19th-Century Historical Herbarium Specimens Reveals the Identity of Five Acorus Species Described by Schott

Heinrich Wilhelm Schott (1794-1865) was one of the pioneering researchers in the taxonomy of the species-rich monocot family Araceae. He described numerous new plant species in various genera, including Acorus, which is currently segregated as a monogeneric family and order occupying a position sister to the rest of the monocots. While describing his new species of Acorus, Schott mostly used characters that are currently considered of low, if any, taxonomic value. His descriptions lack some key characters including, for obvious reasons, chromosome numbers. Therefore, Schott's species concepts cannot be properly interpreted according to the current understanding of the taxonomic diversity of Acorus, even though his species names must be examined for implementation of the principle of nomenclatural priority. The only way of resolving the taxonomic identity of Schott's species names is through the identification of type specimens among historical herbarium collections, by inferring taxonomically significant characters that are missing in Schott's descriptions. On the basis of herbarium collections of the Komarov Botanical Institute, St. Petersburg (LE), we were able to infer ploidy levels of the materials used by Schott to describe Acorus triqueter (diploid, Siberia), A. tatarinowii (tetraploid, China), A. nilaghirensis (tetraploid, India), A. griffithii (tetraploid, Bhutan), and A. commutatus (tetraploid, Bhutan). Leaf anatomy and pollen stainability were used as cytotype markers. All five species belong to the polymorphic Acorus calamus complex that comprises important medicinal plants. Detailed historical and nomenclatural analyses of Schott's species names and herbarium collections are provided.