In an L-system, a string of symbols is repeatedly rewritten using a set of rules. If the symbols are interpreted as a series of drawing instructions, the resulting graphics can resemble organic structures; L-systems can therefore be used to model the development of plants and other lifeforms.

Lsystems implements L-systems in a process-oriented way: each symbol is a process, linked into a string using channels. On each time step, a channel end is passed along the string; each process sends its symbol down the channel, and then replaces itself with the string of processes corresponding to the symbols it should be rewritten to. The symbols are interpreted as turtle graphics commands.