An L‑system (Lindenmayer system, 1968) grows a picture from a tiny
recipe. You start with a short string of symbols (the axiom) and a set of
rules that say how to rewrite each symbol.
Every generation, all symbols are replaced at the same time (in
parallel). Do that a few times and a handful of characters explodes into thousands.
Then a turtle reads the final string like a tiny plotter: some letters draw
a line, others turn or remember a branch point. That’s how a 20‑character
rule becomes a fern.
Biologist Aristid Lindenmayer invented them to model how plants and algae grow —
which is why the branching presets look so organic. Drag the angle slider on the
fractal plant to watch it bend.