Noteworthy CharacteristicsHydrangea macrophylla, commonly called big leaf hydrangea, is a deciduous shrub with a rounded habit that, in the St. Louis area, typically grows 3-6’ tall and as wide unless damaged by harsh winters or pruned smaller. It generally features serrate, obovate to elliptic, dark green leaves (4-8” long) and large clusters of long-blooming summer flowers in either lacecap form (flattened flower clusters of small fertile florets with scattered showy sterile florets often forming a marginal ring) or mophead form (globose flower clusters of mostly showy sterile florets).Mountain hydrangeas are the least common type of bigleaf hydrangea. Scientifically known as Hydrangea serrata, it bears a similar resemblance to lacecap hydrangeas with its flattened heads but has much smaller flowers and leaves. Mountain hydrangeas have hardier buds and thrive in hardiness zone 5 — making them a great choice for areas with late winter cold snaps.