Sensitive growth grammars form an extended variant of L-systems. They were defined by Winfried Kurth and implemented in the software GROGRA. Their definition was guided by the fact that the pure L-systems formalism cannot cope properly with the representation of the great variety of plant architecture and growth behaviour. The new features include:

Global Sensitivity

Global sensitivity means a dependence of growth on the overall structure and not only on neighbouring elements. Examples are

• the dependence on orientation: Plant growth is influenced by the directions of gravity (geotropism) and light (phototropism).
• the dependence on density: Plant parts cannot penetrate obstacles such as, e.g., other plant parts or walls; instead, they have to bypass the obstacle by deviating growth movements.
• the dependence on light: Besides the orientation of light, its mere availability is important. This is influenced by overshadowing by other plant parts and obstacles.

Local Variables

Local variables can be attached to elements of the growing structure. They may represent local properties like carbon or nutrient pools.

Tree Calculations

Tree calculations perform arithmetics on the subtree emerging out of a given element. Such a calculation may determine the total length or mass of a subtree, and these values in turn may have an influence on the further growth of a plant.