The scientific plant name of oakleaf hydrangeas is Hydrangea quercifolia, the species name being a reference to this bush's interesting leaf shape (quercifolia literally means "oakleaf" in Latin). But oakleaf hydrangeas also put out noteworthy white blossoms, which later dry out and remain on the bush for some time.
But what of the genus name, Hydrangea? Well, we're all familiar with the Greek root hydr- as a reference to water, as in "hydrate." Meanwhile, angeon comes from the Greek for "vessel." So in what sense is a hydrangea a water vessel? Well, most species require a lot of watering. Fortunately, oakleaf hydrangeas are an exception in this regard.