Hydrangeas are a diverse genus of flowering plants, prized for their stunning blooms. However, not all hydrangea flowers are created equal. The primary differences between mophead, lacecap, and panicle hydrangeas lie in their inflorescence structure, which is the botanical term for their flower arrangement. This variation is a key identifying feature and is rooted in the genetics of different species and cultivars.
From a botanical perspective, mophead hydrangeas, a type of Hydrangea macrophylla, possess a specific inflorescence structure known as a *corymb*. What appears to be a large, round ball of petals is primarily composed of sterile florets. These florets have sepals that are greatly enlarged and showy (the petal-like structures), but they lack functional reproductive parts—stamens and pistils. Their sole purpose is to attract pollinators to the much smaller, less conspicuous fertile florets that are often hidden within the mass of sterile ones. This massive, globe-shaped display is an evolutionary strategy to ensure high visibility to pollinators, making the mophead one of the most recognizable garden shrubs.
Lacecap hydrangeas are actually the same species as mopheads (Hydrangea macrophylla) and exhibit the same *corymb* inflorescence type, but they display it in a radically different way. Their flower structure is considered more "natural" or ancestral. A lacecap bloom features a central, flattened cluster of tiny, fertile florets that are capable of producing seeds. These are surrounded by an outer ring of larger, showy sterile florets. This two-tiered arrangement creates a landing platform for pollinators like bees and butterflies, which are drawn to the fertile center. This structure is highly efficient for reproduction, as it prominently displays the reward (nectar and pollen) to the intended visitors.
Panicle hydrangeas belong to a separate species, Hydrangea paniculata, and their inflorescence is fundamentally different. They produce a large, conical or pyramid-shaped flower cluster known as a *panicle*. A panicle is a branched raceme, meaning a central stem has multiple branches, each bearing its own smaller flower clusters. Unlike the mophead and lacecap, the panicle's individual flowers are almost all fertile, containing both male and female reproductive organs. However, each small flower also features showy white sepals that attract pollinators. This elongated, often massive, structure is a hallmark of the species and is typically borne on new wood grown in the current season, making these plants more reliable bloomers in colder climates.
