Answer:
The dreadful flower of his range slowly withered means to say a living thing can either die, blossom, or fade. also something that is realistic for the time being and fades away.
Step-by-step explanation:
When we say something is dreadful it means it causes fear or fear arises.
The Chorus uses the metaphor of a "dreadful flower" to represent a living thing that can wither, bloom and die. Similarly, the king's anger came forth into life and then faded away.
The metaphor presents a striking image of something that is true for a short period of time but then dies.