how about starting with simply light densities, and maybe make them simple like uhhh density = prod(sin(coordinate_vector)) because this effectively raises a sine function to a power, the seed may start in a dark area. but it could grow tendrils. they would grow towards the source of most light! the seed gives the tendrils a baseline of energy storage. i guess energy is helpful maybe for growing. maybe each unit of energy lets it grow! i suppose it would grow toward sunlight until the energy it is getting from the sunlight is greater than that it is depleting from growing. then it would stop growing toward the sunlight, and make a chunk root or trunk or something to store the energy it was collecting in that area, maybe sprouting more energy collecting parts, tendrils or leaves. as its root and trunk and bushiness got bigger, then i guess it might send tendrils into dark areas to look for more light! it also might fruit.