
満開って英語で何と言うのでしょう

in full bloom
bloomは咲いている状態、開花という意味です。
Cherry blossoms are in full bloom.
では、植物の構造もついでに。
花びら petal(s)
花粉 pollen
茎 stem
葉 leaf(leaves)
根 root(s)

You, guys, must enjoy viewing cherry blossoms everywhere throughout Japan right now!
Their shining beauty flies like time. Don't miss it, guys who haven't gone viewing them!
everywhere 至るところに
throughout ~じゅうに
Time flies. 光陰矢のごとし。
Have a gorgeous weekend!