Herbaria as a unique source of information for the study of cryptic biological invasions
As a result of environmental changes caused by human activity, many plant species are expanding their geographic ranges, especially eagerly entering disturbed habitats, e.g. ruderal ones. In the case of polyploid complexes, in which cytotypes (polyploidy variants) may show great morphological similarity, such expansions may be unnoticed, taking the form of so-called cryptic (hidden) invasions.
In January, the journal New Phytologist published an article by an international team led by Christoph Rosche (University of Halle) and Patrik Mráz (Charles University in Prague) and including scientists from our Institute, Michał Ronikier and Tomasz Suchan. The authors analyzed several thousand herbarium specimens of Centaurea stoebe L. (spotted knapweed), collected in Europe between 1790 and 2023. Based on specific morphological features, they identified diploid and tetraploid plants and analyzed the dates of their collection and the type of habitat in which they occurred. The IB PAS team was responsible for the molecular validation of the morphology-based identification of the studied herbarium specimens. Using next-generation sequencing, the scientists analyzed the intragenomic variability of the ITS region to detect variants characteristic of diploids and tetraploids. The analysis showed that the identification of diploid and tetraploid individuals on the basis of morphological characteristics, on which the work was based, was almost one hundred percent accurate.
Based on their distribution in natural and relic habitats, the natural ranges of cytotypes were determined. It was found that diploids are present in natural habitats throughout Europe, while tetraploids are present primarily in southeastern Europe. Furthermore, tetraploids have recently started to expand their range towards central Europe, and their proportion has increased rapidly in new, non-native areas, mainly in ruderal habitats. Entering such sites allowed them to expand towards regions with a more oceanic climate. The authors emphasize that such detailed studies of range shifts, habitat preferences and niche evolution are extremely important for understanding the mechanisms of cryptic invasions and the significance of this phenomenon for the proper assessment of changes in global biodiversity.
The work demonstrates how much potential lies in natural collections. The study of specimens and accompanying information from herbarium sheets, combined with modern genetic methods used by IB PAS scientists, allows this potential to be exploited and complex biogeographical problems to be solved.
Original article:
Rosche C., Broennimann O., Novikov A., Mrázová V., Boiko G.V., Danihelka J., Gastner M.T., Guisan A., Kožić K., Lehnert M., et al. 2025. Herbarium specimens reveal a cryptic invasion of polyploid Centaurea stoebe in Europe. New Phytologist 245: 392–405. DOI
Centaurea stoebe L. – fragment of a sheet from the KRAM herbarium.
Photo: IB PAS.
A sheet from the KRAM herbarium – a typical tetraploid specimen of C. stoebe from a ruderal site in Poland (probably the first documented record of a tetraploid in the country).
Photo: IB PAS.
Diploid population of C. stoebe in its natural habitat (near Ramosch, Switzerland).
Photo: Christoph Rosche.
Tetraploid C. stoebe growing in an anthropogenic location, on the edge of a road, in the invasion area (bridge near Závod, Slovakia).
Photo: Christoph Rosche.