there is a freeware book called The Algorithmic Beauty of Plants you can download a PDF file (high quality, 17M)
it contains info about modeling of trees, Fractal properties of plants, Graphical modeling using L-systems, etc etc. contains very good pictures with algorithms.
i see in this forum several very beautiful programs about these goodies such as L-systems.
i see also the Generator of random trees , and even the above seems more beautiful visually but i find the random tree generator more interesting especially when we convert it to a not random generator, since it can display the information like the DNA, and even i think too far, such as prime numbers, who know, the universe is full of surprises.