There are times when an organism undergoes an unusual mutation that makes it unique from others of its own species. In animals, these mutations – often genetic but sometimes caused by environmental factors – can involve relatively fast asymmetrical cellular growth leading to debilitating conditions such as Proteus syndrome, aka the Elephant Man’s disease. In vascular plants, this kind of mutation is often expressed as fasciation – a malformation or “cresting” of the plant along the apical meristem or “growing point.”
Just to be clear, plants (shrubs, trees, cacti, etc.) grow from their tips. If you hammer a nail into a tree trunk, that nail will always stay at the height you placed it because the tree is growing upward from the tips of its limbs, not up from ground level. In cacti, the meristem is at the top of the main body of the plant or along the margins of its limbs (along the edges of pads in the case of prickly pears). Fasciation begins when cells start dividing in an ever-expanding asymmetrical line as opposed to the more symmetrical development of normal cells. This abnormal cell reproduction causes the stems (or flowers) of plants to flatten out into some truly remarkable shapes.
What causes this malformation is not fully understood, although many researchers believe that it’s probably a combination of things. Viruses, fungi, bacteria, genetic abnormalities, and environmental factors such as frost, chemicals, and injuries to the plant are all possible causes that can trigger a plant to start cresting. One researcher thinks that plant hormones might play a significant role in fasciation.
Most succulent species can develop a crested or “monstrous” form. Saguaros, for instance, can grow tremendous fan-shaped crests that can be seen at quite a distance. Some people, notably those in the Crested Saguaro Society (www.crestedsaguarosociety.org), hike through the desert, binoculars in hand, searching specifically for crested cacti. This group has identified at least 2200 fasciated saguaros in Arizona. A CSS member speculates that one in every hundred thousand saguaros might be crested.
Here at Boyce Thompson Arboretum we have several examples of this phenomenon including a crested hedgehog cactus, barrel cactus, and a recently re-planted saguaro. If you would like to see these plants on your next visit, simply ask one of the groundskeepers to show you where they are located.