To be excessively technical, the correct term is "octahedral symmetry"
To be excessively mathematical, no.
I don't thin Minecraft's resolution allows much more complex shapes, and I can't think of anything particular that is smooth and recognizeable. Joining two spheres smoothly might work, or making an ellipsoid.
I'll have to do this too... I was thinking about it, but figuring out how to do my greenhouse really took a lot out of me.
Yeah it's pretty strenuous. Making scaffolding around the entire circumference of the circle while holding down shift every 2 or so rows and then taking it down after is really what kills you. The glass is the fun part =P