Generate Plants procedurally using fractals / L-systems
L-systems are a type of fractal, which was originally invented by a botanist to describe the shapes that plants take. They make a great basis for lots of procedural generation techniques other than plants too.
Here are some explanations and example uses:
Elliander Eldridge commented
Actually, fractal geometry is far from random generation. In the real world, the large and small branches of a single tree follow the same fractal pattern as the large and small tree in that forest. Since this is how nature looks, using fractal patterns instead of random generation of colors and features would make things look more realistic. It could also potentially save on processing power, since the system will always know what would generate at a given coordinate based on the pattern used without needing to store this object positions after world generation.
Stuart Forrest commented
To automatically generate plants to cover a designated area. These plants should be random in color and makeup.