Intraspecific variability of Plagiothecium nemorale complex from the Baltic States

Grzegorz J. Wolski

Department of Geobotany and Plant Ecology, Faculty of Biology and Environmental Protection, University of Łódź, 12/16 Banacha St., 90-237 Łódź, Poland

Plagiothecium Schimp. is a moss genus widespread in Europe and in the world. All species of this genus are highly variable, but among European species the biggest taxonomic problems are caused by Plagiothecium nemorale (Mitt.) A.Jaeger (Iwatsuki, 1970; Lewinsky, 1974; Hemerik, 1989; Smith, 2001; Wolski, 2017, 2018).
The present study is based on the material from: Lithuania (BILAS); Latvia "Silava"; Estonia (TAA), (TU), (TALL), (TAM); and Finland (H). A revision based on 301 specimens,  30 of the specimens randomly were selected for further analysis. Each specimen was characterised on the basis of 15 features, among others: length and width of the leaf, length of costae, length and width cells from the upper, the middle and in the lower part of the leaf. The principal component analysis (PCA) was performed for the average values of all the investigated traits. 
The studied specimens are divided into groups. The length of the cells from the top, from the middle part and the lower part of the leaf has the biggest impact on this division. The axis of the first component separates the examined specimens by the length of the cells of the leaf. Both groups do not differ much in terms of length and width of the leaf. But one group is created by specimens with short and wide leaf cells. This group differs from the other one also by a wider diameter of the stems. While the second group is created by specimens with long and narrow leaf cells. This group differs from the other one also by a narrow diameter of the stems. The averages of the studied characteristics of the compared groups differ significantly statistically (p <0.05) in terms of 11 characteristics.
The obtained results are a premise for the attempt to distinguish two taxa, which are represented by the two indicated groups. Iwatsuki (1970) studying taxonomy of this genus form Japan also distinguishes two taxons - Plagiothecium nemorale and P. nemorale fo. japonicum. Described specimens P. nemorale fo. japonicum (Sak.) Iwats. as a specimens among others, with long and narrow cells. In terms of cell length and width, description provided by Iwatsuki (1970) corresponds to the description of specimens from two groups. This is the first record of this form from the Baltic States.