The two cultivars are very similar (although distinct) and are often mistakenly presented interchangeably in the trade. It would take an expert to distinguish between the two, looking at both side by side and in various seasons, and I don't presume to be one :-)

Waterfall is described as having somewhat larger leaves than Viridis and with more intense fall coloring. Because the individual lobes are clustered so tightly together, they have a more pendulous, flowing appearance which is supposedly the source of the cultivar name.