One I've thought up recently is a semi-carnivorous tree. It doesn't 'eat' meat in the traditional sense, but it lives in regions with very barren soil, so it needs fertilizing supplements (this is why there are so many insectivorous plants; they need the nitrogen that is found in bugs). The roots spread out in the loose soil and greatly weaken the ground in a circle around the tree (not under the tap root itself; the roots are stronger there). The flowers have a sweet smell that attract animals and sometimes people who, if unaware of the tree's true nature, will often fall in among the roots and be unable to escape. There they die, away from the grasp of scavengers and the beaks of vultures. The bodies rot into the soil and give the tree the food it needs, and the wind blows the soil back over the tangled roots to hide where old holes might have been.