Sires are listed alphabetically but you can mouseover each name to see the winning year.
Years only display for winners. For example, Alibhai did not win the Derby, but progeny Dermine (1954) and Decidedly (1962) did.
Grab the data used to create this visualization at Horse Racing Datasets.
Based on D3.js Cluster Dendogram. Please note, this will not look great, or even good, on your phone, sorry!