 Mophead flowers are large round flowerheads resembling pom-poms or, as the name implies, the head of a mop.In contrast, lacecap flowers bear round, flat flowerheads with a center core of subdued, small flowers surrounded by outer rings of larger flowers having showy sepals or tepals.The flowers of some rhododendrons and viburnums can appear, at first glance, similar to those of some hydrangeas.