a rootlike plant stem that grows underground or along the ground surface, is often thickened by deposits of reserve food material, and produces shoots above and roots below (R5)


an association between two or more kinds of organisms in which the parasite obtains benefits from a host, which it usually injures (C2, R5)

Invasive plant

a nonnative plant species that grows quickly and reproduces rapidly, aggressively taking over new areas and outcompeting native plants for light, water, and nutrients (R5, IS1)

Intrinsic value

worth or desirability that is ascribed to something simply because it exists; also known as ‘existence value’ (R5)

Instrumental value

worth or desirability that is ascribed to something because of what it can do for people or a person (R5)

Dispersal mechanism

a means by which plant seeds are spread, enabling the plant to become established in a new area (R5)


continuous or nearly continuous covering of tree branches in a forest ceiling (R2, R5)

Biological toxin

a substance of plant or animal origin that is toxic to other plants or animals (R5)


a method of mitigating the effects of an invasive species by releasing a natural predator from the species’ native range into the environment it has invaded; the use of insects or diseases to control populations of pest insects or plants; also known as


a species not native to a particular area (A3, C4, R5)