Closeup Photo Of A Pink Hydrangea. Hydrangea (Hortensia) is a genus of about 70 to 75 species of flowering plants native to southern and eastern Asia. There are two flower arrangements in hydrangeas. 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, fertile flowers surrounded by outer rings of showy, sterile flowers. The color is affected by the pH of the soil.