Using ideas from formal language theory, Aristid Lindenmayer, a Dutch biologist interested in the development of filamentous organisms, hit upon the idea of generating new character strings from existing ones by replacing given characters with strings of characters in a parallel manner that resembles the growth of living organisms. Przemislaw Prusinciewicz has applied this theory (called Lindenmayer Systems or L-Systems) to model the structure and growth of real plants (see

Przemislaw Prusinciewicz and Aristid Lindenmayer, The Algorithmic Beauty of Plants, Springer-Verlag, 1990).
We can assign to each character in a string of characters a geometric object. For
example: assign to I an internode (or line segment), L a leaf and F a flower. Use brackets to enclose a branch to the left and parentheses to enclose a branch to the right.
The top plant to the right might then be represented as the string
I(L)I[L]IF. The plant below it might be represented as the string
I(I(L)IF)I[I[L]IF]I(L)IF