Morphometry of Chara aspera, C. canescens, C. baltica var. baltica, C. baltica var. liljebladii and C. intermedia oospores: Local variation versus taxonomic differences

Oospores of charophytes allow species delineation in palaeoecology, but are rarely used for determination of recent taxa. Especially in the genus Chara there is no generally accepted catalogue of oospore characters and the existing determination keys do not include brackish water material. Parameters with discriminatory power by statistical analysis are required to exploit the potential of oospore morphometry for species identification. Taking into consideration the conflicting species concepts in use for charophytes, we propose to continue building a database providing information about the parent plant of each oospore, including geographical coordinates and morphological details. This database is used here for the first time to determine which oospore parameters discriminate brackish water charophyte taxa from Germany. The results are discussed in the context of the recent debate of the systematic status of these taxa. In relation to Chara baltica var. baltica (Hartman) Bruzelius 1824, Chara baltica var. liljebladii (Wallm.) R.D.W. 1853 and Chara intermedia A. Braun 1859, our results indicate that C. baltica var. liljebladii is within the variability range of C. baltica var. baltica. On the other hand, C. intermedia and C. baltica var. liljebladii appear better separated in the statistical analyses, but still these two taxa cannot be clearly segregated except for ecological characters as, e.g. habitat salinity and incrustation. The article also presents a method for reliable discrimination between oospores of Chara aspera Willd. 1809 and Chara canescens Desv. & Loisel. In Loisel. 1810.