Cristate or Crest

Cristate forms, or crests, occur when the cells of the growing point of a plant begin to multiply erratically, elongating the growing tip to form "fans", rather than the usual single growing point. This can occur as a result of genetics, or from mechanical damage to the growing tip in the form of sudden cold, insect damage or other causes. When a plant is crested, it develops a form which often is far more attractive and interesting than the normal plant from which it has come."

"The plant showing this abnormal growth are indicated as "forma cristata" or "f. cristata" following the name of the species."

Below is an opinion from Mark Dimmit regarding crest phenomena:
In most of the plant kingdom, the cause of cristation is unknown, but it is usually not a genetic character. Seeds from crested plants rarely produce crested offspring. The garden flower coxcomb (a crested cultivar of celosia) and a couple of succulent Euphorbias are notable exceptions. Crests seem to result from a physical injury to the growing point, perhaps frost, an infection, or insect damage. Crests are often unstable; they can revert to normal growth in time.

Mark A. Dimmitt
Tucson , Arizona ( USA )