Late spring means the Topola (Populus sp.) trees are in full seed dispersal mode and people with allergies are suffering. Ocean is shown above on our bike ride this past Sunday on the trail in New Belgrade. In the Friendship Park, the breezes were spreading the seeds surrounded by the characteristic cotton-like fibers. It was so thick that it almost look like snow. My guess is most of the trees in parks in Belgrade are Grey Poplars, which are hybrids between White Poplars (Populus alba) and the Common Aspen (Populus tremula) to form the Grey Poplar, (Populus × canescens). The Grey Poplars demonstrate hybrid vigor and are much larger than either of the two parent species. They are common in parks in Belgrade and are usually found near the river. There are some big specimens around the city, as you can see on this twitter photo I took on a morning bike ride at Ada Ciganlija. Most of the aspens I see in my home state of Michigan are small and thin, as it is a pioneer species and they are usually seen on disturbed land or secondary forest. Other English common names are poplars, cottonwoods, and aspens.
There are about 25-30 species in the genus, most in the northern hemisphere. It belongs to the willow family. They are mostly harvested for paper or cheap wood products. The genus is common in Serbia, there is even a town near Belgrade named Topola.