In this article, we introduce a new method allowing the computation of the distribution associated to the number of complex structures in plants deriving from GreenLab type growth model. In order to use this method, we set a new mathematical framework based on combinatorics. We show how plants can be seen as plane rooted trees and how their topology can be described by Dyck words. Moreover, we integrate plant growth in the formalism by adapting stochastic F0L-systems to the framework. This new representation enables not only the computation of the distribution associated to all types of organ but also the analysis of particular patterns thanks to a symbolic method. This approach gives new kinds of applications such as estimating the age of a plant from a set of botanical data.