Story related not missable
*** Spoiler - click to reveal ***once you pick up ivy and get the sonic blast for the batmobile, you need to use the sonic blast continuously while following the roots that appear on your radar once at the heart of the roots you need to hold the sonic blast and a plant will burst from the ground.
Enemy militia will start trying to take down the plant, just glide over to them and take them all out. Once the last guy is dead achievement will pop.