Is it "Viburnum x Cayuga" or "Viburnum x Carlcephalum"? I know these are two different types and have different characteristics. How can I tell them apart?
These pics were taken April 15, 2012 in the Chicago area. The plant is roughly 7.0-7.5 feet tall (and slightly smaller width). Vase-like shape with even branching inside. As you can see, it has a nice shape and not a lot of holes.
My inclination would be to say that you have a 'Cayuga' there - especially if it is rarely pruned. If that plant has had the occasional seasonal nip/tuck for form - and I think I can see some relatively long shoots here and there in the third image - then you may have V. x carlcephalum.
'Cayuga' has this great trait of shorter internodes and thus denser habit without excess pruning. 'Cayuga' also tends to have a bit of a ruffle - or waviness - along its leaf margins, which I cannot see in the images provided. It is one really good way to separate this plant from V. x juddii, which is very similar especially when not flowering.
V. x carlcephalum will have a larger framework and will be much less dense, left to its own designs. Coarser in habit, if you will.
The fragrant viburnum clan is tough to tell apart, if you only run across them occasionally - and when they are alone. It is easiest to observe them side by side (like, say, here at the Valley where you might saunter among 125 or so different taxa) and note what you see as differences.
The best thing is that they all smell good, and - as I always say - you can't have too many viburnums...