This tree is getting very common nowadays. The hardiness of this plant is simply amazing. You can see it growing out of roof, concrete crack of building or concrete fence.
On close examination, it has tremendously strong, thin and penetration root which can suck out any nutrient from the concrete wall. It also seems to be able to control the amount of water needed to withstand "long" drought... ie, a week without rain would mean that the wall is absolutely dry and yet, it has no effect on the plant. Does it mean that this plant actually absorb water moisture from the air? Whatever, scientist should have a study on this plant. Perhaps, on day, we have vegetable growing on walls rather than in bed of soil!
Look at the above plant, the leaves are green and healthy even without fertiliser.