Not only do plants have to worry about getting chopped, stepped on, eaten by animals and picked for our consumption, but they also have to worry about other plants!
Plants are used to competing with other plants for sunlight, water and nutrients, but they also have to compete with other plants that literally grow on them.
There are some plants that are parasites, and attach themselves to the roots or stems of a host plant to siphon off nutrients.
It can be a problem for farmers when their crops are attacked by parasitic plants. Parasitic plants are such a problem in Africa, that farmers there plant their fields twice, first with plants that resist the parasites and then, after the would-be parasites have died, with regular crops.
A researcher at Harvard, Kristin Lewis, studies how plants and their parasites might communicate. For example, there's some evidence that when an insect attacks a parasite, the host plant might be called on to provide extra defensive chemicals to ward off the insect. The parasite can actually be useful by alerting the host plant to the danger and boosting their overall defenses.