In plants, meristem is undifferentiated tissue capable of active division and differentiation into various types of cells. Apical meristems are those found in the tips of plant roots and stems where they are commonly called growing points. Apical meristems are responsible for growth in length.
Rarely, the apical meristem elongates perpendicular to the usual direction of growth resulting in flattened, fan-like, ribbon-like, coiled or contorted stems and plant tissue. The resulting structure is called a fasciation. Although fasciation most often occurs on stems, flowers, fruits and other plant parts can show this anomaly.
A mutation in a single gene in the central meristem tissue appears to be the cause of fasciation. Some species develop this condition more readily than others suggesting a genetic component. Other causes might be growth hormone imbalance within the plant, environmental factors (temperature, lack of water, chemical exposure, radiation), mechanical damage or attack by bacteria, viruses or fungi. A fasciation does not harm the plant and is usually not passed on to future generations.
The center picture shows a woolly mullein (Verbascum thapsus) fasciation. The other two photographs are of a normal plant and inflorescences. The fasciated plant was growing near Baum Lake in Shasta County CA.
A previous post of a cristate saguaro cactus (Cristate Saguaro 03-27-19) is another example of a fasciated (sometimes called crested) plant.