Literature Reference: 菀彼桑柔，其下侯旬。——《诗经·小雅·鹿鸣之什·桑柔》 Lush and tender are the mulberry leaves, beneath them lies a shady haven. Source from 'The Book of Songs'.
于: Thus, it is.
菀: The lushness of vegetation.
Meaning: Lush and tender, symbolizing vitality and beauty.