Defeating them unlocks Up to No Gourd medal.
This bounty hunt is very easy if you play by the rules. While you are defeating the Wildflowers, a Squash will be following you. If you touch the Squash, you die and the bounty hunt immediately ends. Jumping off the edge of the map or respawning from the pause menu will also cause the bounty to immediately end with the message "play fair" appearing on their screen, possibly due to players trying to escape the Squash that way as getting vanquished does not end the bounty.
Getting vanquished normally without being killed by the Squash or jumping off the map will NOT end the bounty, so don't be afraid to charge into battle, just watch out for the Squash and the map edge. Each time you defeat a Wildflower, check the Squash's current position and try and keep your distance from him. If the Squash is very close, then try sprinting or using an ability such as Warp.