Spiral Phyllotaxis and the Golden Angle
The disposition of the leaves in your picture is not as simple as it seems. That's a spiral phyllotaxis, which can be very complicated.
The plant in your image is a houseleek, a plant from the Genus Sempervivum.
In those plants, according to Jeremy Burgess (Introduction to plant cell developmnent):
... leaf primordia are separated from each other in an angular arc that approaches 137°.
By the way, 137° is (almost) the golden angle (φ).
Here is an image explaining the phyllotaxis of Sempervivum (from Burgess, 1989):
Even more interesting is the pattern made by the 137.5° GA spiral of Aloe polyphylla:
Sometimes this can produce invisible spiral patterns, a phenomenon called parastichy:
Source: Burgess, J. (1989). An introduction to plant cell development. 1st ed. Cambridge [etc.]: Cambridge University Press.
PS: I know that this is off-topic, but I'd like to share this video from Cristóbal Vila, which deals with Fibonnaci sequence, golden ratio and golden angle in nature. Look at the flower disposition at 1:44 : https://www.youtube.com/watch?v=kkGeOWYOFoA