Comparative pollen and phytolith collections

Pollen collection

The basis of the pollen collection was created in 2000-2006 by Miloš Kaplan (1969-2006) as part of his doctoral studies at the Department of Botany. He identified plants and collected their flowers directly in the field, mostly in the Czech Republic, and occasionally during his study trips to neighbouring countries. The resulting material was processed in the Palynology Laboratory of the Institute of Archaeology of the Czech Academy of Sciences, Prague. Originally, the material was processed by acetolysis according to Erdtman (1960) and the pollen grains were then stored in vials containing glycerol. However, this medium has since been found to be unsuitable: the pollen grains swell in it and can completely disintegrate over time. It is recommended that the glycerol samples be transferred to a more suitable medium or replaced with a new material. The collection will be supplemented with new taxa (and with the same taxa collected in other areas).
The pollen collection is stored in the Rudolph Laboratory of Palaeoecology on the 1st mezzanine of the Department of Botany, Benátská 2, Prague. At present (2024) it contains almost 800 plant species, of which 500 are available in the form of permanent preparations, while the remaining 300 specimens need to be revised or even completely restored due to pollen degradation. The permanent specimens are stored in glycerine gelatine sealed with natural waxes to prevent drying out. The pollen collection is primarily used as a reference collection for pollen analysis and teaching.

Phytolith collection

A large number of plants store silicic acid from the soil solution in their cells, giving rise to the so-called biogenic opal, also called phytolith (Piperno 2006). When plant parts die, the microscopic phytoliths are released back into the soil where they persist across a range of environmental conditions. Phytoliths can persist for up to hundreds of thousands of years in different types of sediments such as loess, which often form continuous series across the Quaternary, yet are not amenable to pollen analysis. Therefore, phytoliths have gained attention as one possible method of paleoecological research. Graminoids (both grasses and sedges) produce up to an order of magnitude more phytoliths than other taxonomic groups. Moreover, phytoliths of grasses can in some cases be distinguished down to the species level. Therefore, this comparative phytolith collection also focuses mainly on representatives of the family Poaceae.
The basis of the phytolith collection was created by Kristýna Hošková when she collected material for her thesis at the Department of Botany in Sudan in 2014. Later, she began to systematically collect Central European grasses and the method of collecting and storing the material gradually became more formalized (see below).
The phytolith collection is housed in the Rudolph Laboratory for Paleoecology, 1st mezzanine of the Department of Botany, Benátská 2, Prague. At the moment, it includes a total of 75 species of the family Poaceae, collected in repetitions at fifteen localities in the Czech Republic, Poland and Slovakia. The collection also includes some species of sedges and rushes and some dominant European woody plants. In addition, it contains 15 species of grasses collected at various localities in Africa, mainly in Sudan, Botswana and Zimbabwe. The African collection also includes several items of species from families other than grasses, these being palms, sedges and nettles. Each phytolith reference sample refers to a herbarium item that was collected in the field. Individual collection sites were labeled with species composition descriptions and located in GPS. Separation of phytoliths from plant leaves was done using in situ charring method (Kumar et al. 2017). Selected leaf segments were charred for 3H at 550°C directly on a glass slide. Permanent preparations were made from the phytolith samples extracted from the plants. Glycerin was used as the medium, and the samples were "sealed" on the slide with wax. Photographs of the phytoliths were also taken at 400× magnification.The shapes of the phytoliths of selected species were digitized and processed using geometric morphometric methods.
The aim of the ongoing project at the Department of Botany of the Charles University is to start a systematic compilation of a comparative collection for the needs of paleoecological research in Central Europe:

1. describing the diversity of phytolith shape in currently important grass species of Central Europe, but also those that may have been dominant in earlier periods of European natural history (e.g. glacial relicts);
2. describing the variability of phytolith shape at the individual level in order to capture the possible relationship between phytolith shape and the environment.

References:

Erdtman G. (1960): The acetolysis method, a revised description. Svensk Bot. Tidskr. 54: 561-564.
Kumar S. & Elbaum R. (2017): Estimation of silica cell silicification level in grass leaves using in situ charring method. Bio-protocol 7 (22): e2607. D
Piperno D.R. (2006). Phytoliths. A comprehensive guide for archaeologists and paleoecologists. Lanham, New York, Toronto, Oxford: AltaMira Press (Rowman & Littlefield).