Parasitic plants: hooking up with host plant stealing sugars.
An indirect parasite, steals sugar from mycorrhizae
Other examples: mistletoe, dodder- no longer photosynthetic
Some species have roots that function as haustoria (nutrient absorbing projections that enter the host plant)
Carnivorous plants: nutrients nitrogen and phosphorus from insects- carnivorous plants need nutrients because of their nutrient poor soil
I hope this helps! ♥