We have been growing Doublefile Viburnum (Viburnum plicatum tomentosum 'Mariesi' ) for 13 years. That means our shrub has reached its mature size (about 10' high and 15' wide) and is a spectacular sight at this time of year. You'd think after enjoying its performance all these years, we would have realized why it's called "Doublefile" before now.
While we were admiring it this spring, we realized that the spreading horizontal branches literally have double rows of flat clusters of flowers. They resemble lace-cap hydrangeas which often confuses people who are not familiar with the plant.
Though it is a large shrub, the fact that the flowers "float" above the branches gives it an airy appearance. Later in the summer there will be berries and then wonderful fall color, making it a multi-season addition to the garden. Though it takes a few years to begin to develop its horizontal structure, it's well-worth the wait.