The plant people occupied the very top of the ecological niche. They absorbed the first rays of light from space, while their flourishing branches and leaves also blocked other lower-level life from obtaining enough energy.
And so, at last, relying on their own advantages, they ruled the entire planet and became the undisputed planetary overlords of that age.
To obtain more sunlight, they grew larger and larger, taller and taller.
But as their bodies swelled in size, their mass also grew greater and greater. As a result, the energy they consumed increased as well. The greater and more numerous their energy needs became, the more they had to stretch their branches and leaves higher, larger, and denser.
The cycle repeated itself again and again.
The evolution of the plant people seemed to have entered a dead loop. They grew larger and larger, each one like a towering tree—a towering tree that could move.
Of course, not all plant people evolved into towering trees. Some plants still occupied the lower ecological niches, living off the pitiful scraps of sunlight that leaked down.
Moreover, the plant people's bodies did not keep increasing in size forever, because two-dimensional gravity existed, and the "cells" that made them up knew when they ought to stop.
Likewise, although gigantism won them a higher ecological niche, their increased mass ultimately made their movements sluggish.
And that sluggish movement just happened to delay the time of their extinction. Because they moved slowly, they spread slowly; because they spread slowly, the rate at which they occupied the entire planetary horizon remained slow.
Just like that, the plant people of the Congestion Era spent almost three hundred million years evolving from tiny plant people into towering-tree plant people, and finally occupied the entire horizon of the planet.
And then, they