poplar fluff on a tree branch against the blue sky

allergen allergenic allergic background biology bloom blossom blue branch bright catkins city close closeup cotton cottonwood cottony dangerous deciduous dioecious ecology environment family fastgrowing flower fluff fluffy foliage fragment fresh genus green greens grow growth heat hot inflorescences june leaf many monoecious natural nature nobody outdoor plant poplar problem rarely season seasonal seed seeds sky spring summer topol tree trees white willow