Scholars and scientists at the University of Cologne research, explore and experience Cologne. They contemplate the flora, fauna and last but not least the past and present inhabitants of the city. In this section, they report on all things interesting, quirky, typical or less familiar. Dr Gregor Schmitz from the Institute for Plant Sciences on a small weed of great scientific significance.

It can be found in many places in Cologne: on meadows, in parks, along the roadside between cobblestones, on small walls and growing out of house walls. On my daily way to the university, I notice many specimens of thale cress, or Arabidopsis thaliana, as it is called in scientific contexts.

The small plant is not only a survivor in a wide variety of urban environments, it is also a star of plant research: No model organism is used more frequently. The genome of A. thaliana has been fully sequenced since the year 2000. Its relatively small genome, short generation cycle and robustness make it the perfect candidate for research on diseases or genetic changes that also affect other, more complex plants.

The thale cress plants used in research are a genetically ‘pure’ type: The line called Col-0 comes from a single individual of the plant. In the wild, A. thaliana has a greater genetic diversity; there are different regional types spread over four continents.

Recently, together with Professor Dr Juliette de Meaux and other partners, I conducted a study on the life cycle of the plant. For example, we wanted to find out how wild types with their respective genomes adapt to local environmental conditions such as temperature and human disturbances. We also wanted to better understand how the findings gained in the laboratory during research on the ‘pure’ model organism are reflected in genetically different lineages. I collected the plants we examined on my daily bike ride from Rodenkirchen to the university – there is a considerable variety of specimens.

This made us realize how great the ecological diversity in our streets is: Even in the area limited to the south of Cologne, there is a multitude of different lineages. The sequencing of plant genomes revealed that the urban lines are not more closely related amongst each other than to lines from the larger region.

In addition, the A. thaliana populations in Cologne show very different life cycle characteristics. These differences contribute to their persistence in habitats that mainly differ in how much they are disturbed by human activities – such as weeding or mowing. The plants also have different strategies for their respective locations (cool and wet or hot and dry). For example, some plants can prevent themselves from germinating when it is too hot because they would then dry out.

Such high genetic diversity in such a small area surprised us. It is not randomly distributed, but corresponds to the specific differences in the urban environment. How exactly the thale cress adapts to the urban environment – often under conditions of advanced environmental destruction – will be a matter of further concern at the Institute for Plant Sciences. Certainly, insights into how this model plant adapts to the rapidly changing conditions of the city will help us understand how climate change will affect many other plant species.