This article is from the Fractal FAQ, by Ermel Stepp email@example.com with numerous contributions by others.
A L-system or Lindenmayer system is a formal grammar for
generating strings. (That is, it is a collection of rules such as replace
X with XYX.) By recursively applying the rules of the L-system to an
initial string, a string with fractal structure can be created. Interpreting
this string as a set of graphical commands allows the fractal to be displayed.
L-systems are very useful for generating realistic plant structures.
Some references are:
1. P. Prusinkiewicz and J. Hanan, _Lindenmayer Systems, Fractals, and
Plants_, Springer-Verlag, New York, 1989.
2. P. Prusinkiewicz and A. Lindenmayer, _The Algorithmic Beauty of
Plants_, Springer-Verlag, NY, 1990. ISBN 0-387-97297-8. A very good
book on L-systems, which can be used to model plants in a very realistic
fashion. The book contains many pictures.
More information can be obtained via the WWW at:
http://hill.lut.ac.uk:80/TestStuff/trees/ 3 Dim. L-system Tree program