Although there are no plants that have been documented combusting
on their own, there are indeed plants which use fire
as a weapon to weed out competitors. These plants are quite flammable, and when conditions are right, a fire will rage through the ecosystem, burning everything to the ground, or at least roasting the plants back to the main stems. Although all plants are scorched, the flammable plants are adapted to fire
and spring back into action, sometimes within days. They outcompete neighboring plants, and even 'feed' on their nutrients after the fire. Nature is brutal.
Examples of this phenomenom are found in Chaparral environments of California, closed-cone pines such as Knobcone Pine which release seed immediately after fires, and Euchalyptus forests in Australia which can resprout from the trunk after a fire.