Each item in Minecraft has a unique ID assigned to it, known as an item ID, this can be used in commands to spawn the item into the game. The item ID for wither rose in Minecraft is shown below:
The Wither Rose item can be spawned in Minecraft with the below command. Cheats must be enabled before this will work.
Below is a table of the tools that can be used to break Wither Rose blocks, and the speed it will take to break at (in seconds). This is calculated with the formula (1.5 * Block Hardness) / Tool Multiplier.