What causes a crested saguaro cactus? Here's everything to know about these gnarled giants
The saguaro cactus is the symbol of the Southwest. Its shape is so iconic that it has become an emoji representing all kinds of cactuses. But the saguaro's distinctiveness doesn't stop there.
The long-lived, many-armed giants of the Sonoran Desert have another quality that makes them stand out. Some specimens aren't perfectly cylindrical — they exhibit an irregular fanlike shape at the top. These are crested — or cristate — saguaros.
The Arizona Republic talked to two experts to learn how crested saguaros develop. Bill Peachey is an independent research ecologist and Peter Breslin is a plant ecology researcher at Tumamoc Hill Desert Laboratory at the University of Arizona in Tucson. Here's what they had to say.
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What is a crested saguaro?
The saguaro belongs to a large suite of cactuses called columnar cacti, so named for their shape. Characteristics include elongated and cylinder-shaped bodies, woody internal ribs that support their stature and prickly spines.
A crested saguaro is one that mutates at the top and develops a broad, fanlike formation instead of a rounded tip.
What causes a crested saguaro?
Breslin will be conducting the seventh survey since 1908 of a stand of saguaros at Tumamoc Hill Desert Laboratory, an 860-acre national historical landmark that doubles as an ecological and archaeological reserve. He said there is no scientific proof of what causes a crested saguaro, but there are several theories.
One is that frost triggers the mutation, Breslin said. There's also an idea that saguaros near power lines are more likely to branch into the fanlike shape due to the magnetic field created by power lines.
“It could also just be a random mutation that happens that causes the plant to grow out into rows of growing cells instead of one,” Breslin said.
“With saguaros, it doesn't seem hereditary, like it's not a mutation that's passed onto future generations. It seems to occur as an acquired mutation. So then that's about all we know at this point with any certainty."
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Is a crested cactus sick?
Peachey has been surveying the same cactuses on state-owned land near Rincon Valley, southeast of Tucson, for over 26 years. He attributes the formation of the crested shape to phytoplasmas.
Phytoplasmas are tiny, plant-infecting organisms carried by microscopic leaf hoppers like mites that suck on plant juices and cause a hormonal imbalance in the plant, Peachey said.
“A protein covering in the phytoplasma found in plants turns on growth in the plant,” Peachey said. “So these little tiny plant-sucking organisms have trouble biting that plant, so they need to be on growth where the skin is soft and they can get in there.
“So the phytoplasma’s deal with the organism is that I will force the plant that you want to eat to grow new tissue so that you will have more to eat and, in return, you will host me and carry me from plant to plant.”
Peachey says phytoplasmas have infected over 300 kinds of fruit trees worldwide and their damage is called yellowing.
“This infection has done terrific damage to our food supply,” Peachey said. “And the fact that it's on our cactus ends up with a very strange and beautiful growth form. But it's not killing the plant.”
How many crested saguaros are there in Arizona?
The Crested Saguaro Society, a volunteer group of naturalists who document cristate saguaros and other cactuses around Arizona, California, Nevada and Mexico, has documented over 3,100 crested saguaros. To learn about the group and see photos of the crested saguaros they have identified, visit https://crestedsaguarosociety.org.
How big is a saguaro crest?
According to a fact sheet on Saguaro National Park's website, saguaro crests generally measure between 3 and 5 feet in diameter. Peachey said if you look closely, you will notice that the crests only grow in one direction.
“The pleat crests as (it grows) and the whole thing starts twisting to the right,'' Peachey said. “They always twist to the right. If you ever see one that twists to the left, you let me know."
Do other cactuses develop crests?
The crested growth form is not unique to saguaros, Peachey said. It can be be seen in barrel and other columnar cactuses as well as some succulents, such as crested euphorbia.
“You can get crests in other cactuses,” Peachey said. “In fact, barrel cactuses are more commonly crested than saguaros. They're just not pretty and they're also down in the vegetation and the terrain behind trees and shrubbery and you don't see them from a long way away.”
Where to see a crested saguaro
Crested saguaros can be seen wherever saguaros are common. You just have to keep an eye out. Here are places to look.
Visit Saguaro National Park, particularly the Tucson Mountain District west of downtown. Choose one of the hikes or scenic drives and start looking. Arizona Republic contributor Roger Naylor spotted a crested cactus on the Loma Verde Trail in the park's Rincon Mountain District east of downtown.
There's a double crested saguaro in Coyote Canyon in the McDowell Sonoran Preserve. Use the Granite Mountain trailhead at 31402 N. 136th St., Scottsdale, and bring a map. The nearly 7-mile route through the canyon involves several trails.
For an easier outing, look for the crested saguaro at Desert Botanical Garden in Phoenix.
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Is it illegal to cut a crested saguaro?
The growing human population, land development, theft and vandalism are some of the biggest threats to saguaros, according to the National Park Service. That's why many plants —including saguaros — are protected under Arizona's native plant law.
Destruction or theft of a saguaro is illegal under Arizona law and can result in fines and a Class 4 felony conviction.
Arizona law says that landowners can destroy or remove plants on their land, but only if the land is privately owned and protected plants are not taken off the land or offered for sale. The law requires that the landowner notify the state 20 to 60 days before the plants are destroyed.
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