From Halopedia, the Halo wiki
Fractal plant refers to a type of vegetation found on the Forerunner world Genesis. As noted by Linda-058, the planet's landscape is ambiguously both natural and artificial, thus making it impossible to determine the plants' real nature—though such matters generally arise on most Forerunner installations. Genesis itself is an artificial planet, though.
Fractal plants may vary greatly in size. While some are not taller than a person, others may be as tall as mountains.
List of appearances