They are a result of light bouncing off glass surfaces inside the lens, Lenses with large numbers of elements such as zooms tend to exhibit greater lens flare, as they contain multiple surfaces at which internal bouncing can occur.
Wide angle lenses also tend to exhibit flare simply due to the wide angle of acceptance to incoming light. Typically a bright light source like the sun or high intensity street light is needed to create them. Another photographers flash can also do it, but near impossible to control for creative purposes.
The more blades in the camera the rounder the flare light. 5 blades give a pentagon, 6 gives a more rounded but still noticeable hexagon, 8 looks pretty much like a circle in most cases. Mike_E do they make lenses without blades? You need the blades for the aperture, so how can you have a lens with no blades?