Orpiment Jewel
This curious offshoot from the Crystal Peridot was cast into lush areas, filled with both food and competition. From their abundance of food, trace waste products accumulated in them, which were then expelled into the ground. This waste product contained trace toxins, which could kill small land flora and microorganisms that it could then decompose. Over time, its waste products were elaborated into a rudimentary poison used to kill not only for food, but also to remove competition. Individual crystals don't do much, but large colonies of them can slowly devour many small flora, only leaving the larger flora. Though it does kill these important parts of the forest, it does so slowly and weakly enough so that new plants can replace what the Orpiment Jewel removed.
While it still retains photosynthesis, it photosynthesizes to a lesser degree than its ancestor, due to its ability to kill other crystal flora.