The giant saguaro cactus is a universal symbol of the American west. These plants are native to only a small region of southern Arizona, the adjoining Mexican State of Sonora and extreme southeastern California, yet their tall, columnar shape is familiar to any desert traveller.
The saguaro cactus is composed of a tall, thick, fluted, columnar stem about two feet in diameter with several large arms that curve upward in the most distinctive conformation of all Southwestern cacti. But sometimes they produce a fan-shaped form of uncontrolled growth at the tip. These odd growths are referred to as cresting (or cristate), and are very rare occurrences. It is estimated that this condition affects approximately one out of every 200,000 saguaros. Originally, less than 200 of these abnormalities were thought to be in existence. However, more than 2,000 have been discovered so far, and biologists believe that there may be many more.
A crested saguaro Photo credit
The cause of cresting, also know as fasciation, in saguaro is not fully understood. Some speculate that it is a genetic mutation, or caused by micro-organisms, or physical damage such as lightning strike or freezing.
According to Scottsdale Convention & Visitors Bureau, “the most widely accepted explanation is that cresting is caused by damage to the apex, either mechanically (man made or nature-caused) or by freezing. The crest doesn’t harm the saguaro, which can continue to produce flowers and fruit.”
The National Park Service website wasn’t very helpful, but Wikipedia has a general article on ‘fasciation’ which attributes this abnormal growth in plants to a wide range of factors including hormonal, genetic, bacterial, fungal, viral and environmental causes.
Quoting directly from the article:
Fasciation can be caused by hormonal imbalances in the meristematic cells of plants, which are cells where growth can occur. Fasciation can also be caused by random genetic mutation. Bacterial and viral infections can also cause fasciation.
Additional environmental factors that can cause fasciation include fungi, mite or insect attack and exposure to chemicals. General damage to a plant's growing tip and exposure to cold and frost can also cause fasciation.
There are many places within Saguaro National Park where you can see these unique specimens. There are at least 27 documented crested saguaros on the East side of the National Park, and 30 on the West.
Two normal saguaros. Photo credit
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