floating fluffy 飞絮

The Beijing authorities have vowed to take action on the floating fluffy tree seeds that irritate capital residents every spring, ending the problem by 2020. 

北京市有关部门表示要采取行动治理每年春天都困扰首都居民的飞絮，到2020年彻底解决该问题。

Beijing has about 2 million female poplar and willow trees which produce catkins to spread their seeds every spring, the Beijing Municipal Bureau of Landscape and Forestry (BMBLF) was quoted as saying on Wednesday by the Beijing Morning Post. 

据《北京晨报》援引北京市园林局的信息显示，目前，北京约有200万株杨柳树雌株，每年春季都产生大量飞絮。

Catkin特指那些“絮”，fluffy catkins就是漫天飞舞的杨柳“飞絮”，产生飞絮的是杨柳树雌株（"female" willow and poplar trees）。