L-Systems

Q13: What are L-systems?
A13: 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:

More information can be obtained via the WWW at
http://life.anu.edu.au/complex_systems/tutorial2.html and a L-system leaf can
be viewed at gopher://life.anu.edu.au:70/I9/.WWW/complex_systems/leaf.gif .