This is a story related achievement that should unlock once you leave the train station and arrive at the Ghetto (after the loading screen and once you regain control of your character).
For me it didn't unlock. I had to walk to the left to pick up Flower #7, then walk back to the starting point, go back and forth for about 20 seconds and then it finally unlocked. So if it doesn't unlock for you, try just going back and forth between the start and the flower to the left until it does.