This is close-up photograph of dandelion seed heads. In Japanese, we call them "Wata-boushi" that means a cap of cotton. I search the word of "Wata-boushi" for explaining in English . But I didn't find match word via online English dictionary.
Finally I know it is called "Dandelion clock" according to en.wikipedia. It is difficult to imagine from the shape.
タンポポの綿毛は英語で "Dandelion clock" と表現するらしい。最初から表現が分かっていれば調べやすいが、想像できないような言葉である場合は調べのは大変だ。