Few days ago, I found a strange pollen grain that I couldn't identify. All candidates I had in mind did not perfectly match what I could see at the microscope. Is it a strange Fabaceae, a strange Gentianaceae, a strange Helianthemum? No idea. Even with the rescue of my colleagues Burgi and Daniela, we couldn't come to a convincing decision.
Finally, I moved forward and I slept on it a few nights. And then enlightenment came to me all in a sudden, it's a pollen from Cornus sanguinea! Cornus sanguinea – the common dogwood – is a widespread shrub over temperate Europe, rather common on calcareous (alkaline) soils. Its species name (sanguinea) probably comes from the red colour that get the younger twigs when exposed to sun light.
The common dogwood is an entomogamous species, meaning its pollen grains are dispersed by insects. In this particular case, mostly by bees and bumblebees (Guitán et al. 1996). Pollen grains from entomogamous species and rare in palynological samples, therefore it is often difficult for palynologists to identify them, but always a nice surprise!
Pollen grain of Cornus sanguinea. The scale bar represents 50 µm.
Interesting fact: dogwood was used in one arrow carried by the Iceman in the Neolithic in the Ötztaler Alps (Oeggl 2009).
This pollen grain comes from the Mondsee Lake, in Austria. It deposited on the sediment surface of the lake at about 2000 BCE, and was then progressively buried under almost 5.5 m of younger sediment. It remained there for 4000 years, quietly waiting for us to recover it :)