Cresting and Waving
The growing tips of most normal plants grow in a somewhat cylindrical and vertical fashion with a defined tip or apical meristem and branches or side shoots beneath it. As the tip grows, throwing new leaves and branch buds, it continues upwards as a single main tip. Occasionally this process goes awry and the meristem begins to grow horizontally instead of vertically, causing a flattened, often wavy or curved structure instead of the typical stem. This phenomenon is known as cresting or fasciation, and a fasciated plant is also referred to as "cristate". An example of a fasciated tip on a Saguaro cactus stem is shown in the thumbnail picture. This can occur at branch tips, in flowers or inflorescences and in roots as well. The results can be quite bizarre, humorous, or even extremely ornamental. Sometimes a normal appearing plant will show cristation in the inflorescences only. A familiar example of the very ornamental type of fasciation is the blooms of the cockscomb Celosia. These are grown from seed and the cristate flowerheads come true from seed as well.
I believe that my first experience with a crested plant was when I saw a fasciated cactus. I'm not sure if it was a true cactus or from the genus Euphorbia, as both groups have a number of members that can exhibit this type of growth. However, it was impressive because I remember that the plant was all convoluted, somewhat like a botanical version of a brain! These plants do not grow vertically very much after they become fasciated, so they end up getting wider over time, rather than taller. This is why an old cristate cactus that is normally round will take on the appearance of a brain over time. I even saw a picture of one young specimen that looked like a frowning face; the plant was aptly named "Sad Sack"! Another one looked like a smiling face. One of the fascinations of this phenomenon is the unusual forms that can result, especially in cacti and succulents.
The cause of fasciation is still not completely understood. Sometimes it appears to be a mutation that is inheritable, as in Celosia, while other times it appears the result of injury either by insects, pathogens, or mechanical damage. One time I was growing a balsam plant (Impatiens balsamina) and I knew that when they began flowering, the vertical growth slowed down drastically. So I decided to do a little experiment in which I pinched off all the flowers just after they faded, so as to prevent any seed production. Normally this plant grew about 18 inches tall, but my balsam ended up about 5 feet tall before it was over with! Additionally, a side effect was when it reached this size, the terminal growing point became fasciated. Of course, the vertical growth stopped then, but I was quite interested in this unusual development. Perhaps preventing the plant from seeding threw the hormonal balance off and helped to induce the cresting.
Something else I have observed in regards to fasciation is that on occasion a perfectly normal branch will spring from a fasciated growing point. This observation would seen to indicate that the phenomenon is reversible. It also suggests to me that the unusual growth pattern may be the result of a triggered gene that can be turned off or on under the right conditions. A close look at the photo above, left, reveals some normal heads among the fasciated mass of Mammillaria geminispina 'Cristata' as well as some "smiles" and "frowns".
All in all, the phenomenon of fasciation adds more interest to our enjoyment of plants, and can be an unexpected surprise in our gardens as well.
Image credit: James G. Howes and Public Domain image