Aristid Lindenmayer, a biologist, proposed in 1968 that plant growth could be written as grammar: start with an axiom string, apply rewrite rules to every symbol at once, repeat. F becomes F[+F]F[-F], brackets push and pop position, plus and minus turn. Feed the final string to a turtle-graphics interpreter and a branching plant appears, and a few iterations of a one-line rule produce structures of startling botanical accuracy.
The compression is the marvel. A fern is a rule, not a model; an entire species’ silhouette fits in a sentence. Randomizing rule choices gives every rendered plant individual variation within a family resemblance, exactly like real vegetation, and 3D versions with leaves and tropism grow the foliage of games and films.
Beyond botany, L-systems draw classic fractals (the Koch snowflake and dragon curve are two-rule systems) and generate architecture, road networks, and lightning. For audio-reactive work the growth process itself is the material: a structure that visibly grows on sustained energy, branches on accents, and sheds or withers in the quiet is narrative motion, change with a direction, which reads far stronger than looping ornament.