What is a Saguaro Cactus
Saguaro Cactus Overview
The Saguaro Cactus is one of the most iconic plants of the American southwest achieving tree-like size without having a single leaf or wooden branch on it. Found in the Sonoran Desert, the Saguaro Cactus is the largest cactus in the United States growing up to 50 feet tall with one reaching a record 78 feet in height.
While these cacti can be taller than some buildings, they take a really long time to grow to monstrous heights. A Saguaro Cactus may take up to 30 years to grow taller than a human and over 100 years to break 25 feet. Even though that seems like a long time, and it kind of is, Saguaro Cactus routinely live to around 150 to 200 years old. What’s even crazier is that when these cacti are fully hydrated and mature, they can weigh up 5,000lbs.
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A study called “Physical Determinations of Growth and Age in the Giant Cactus”, posted in the Journal of the Arizona Academy of Science has made a table to estimate how old a Saguaro Cactus might be based on its height which will be posted below:
| Height | Age (Years) |
|---|---|
| 0.5 feet (0.15 m) | 9 |
| 1.0 foot (0.30 m) | 13 |
| 5.0 feet (1.5 m) | 27 |
| 10.0 feet (3.0 m) | 41 |
| 20.0 feet (6.1 m) | 83 |
| 25.0 feet (7.6 m) | 107 |
| 30.0 feet (9.1 m) | 131 |
| 35.0 feet (10.7 m) | 157 |
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Taxonomy
Its scientific name is given in honor of Andrew Carnegie.
- Kingdom: Plantae
- Clade: Tracheophytes
- Clade: Angiosperms
- Clade: Eudicots
- Order: Caryophyllales
- Family: Cactaceae
- Subfamily: Cactoideae
- Tribe: Echinocereeae
- Genus: Carnegiea
- Species: C. gigantea
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Size and Body Description
The Saguaro Cactus is a round, column-shaped cactus that grows what can only be described as arms that shoot off of the main body of the cactus. As many as 50 of these arms can be seen on a cactus if it’s allowed to grow fully and none are broken off over time. There are instances where you can find a tall cactus without any arms but that doesn’t mean it’s defective. Armless Saguaro Cactus are called spears and the reason for this happening is still somewhat of a mystery.
In order to support the cactus and all of its arms, Saguaro Cactus can grow up to 30 inches in diameter. To put that in perspective, the average car wheel is around 14 to 19 inches in diameter and these cactus can nearly double that. Alongside its massive size above ground, the Saguaro Cactus has a root system that is equally large in order to pull the most nutrients out of the harsh desert soil it can. The root system has a combination of shallow and deep roots that help collect whatever water is available.
The Shallow roots are typically only 3 to 6 inches deep but can extend outwards of up to 100 feet to allow for maximum rain capture during the monsoon season. The deep roots of the Saguaro cactus are called taproots which can extend downward anywhere from 3 to 5 feet and are used to “tap” into groundwater that may be below the surface.
On the subject of water collection and conservation, the Saguaro Cactus has evolved a skin or bark that is suited to reduce its water usage and loss. The outer layer of the cactus has a waxy coat on it that essentially waterproofs the plant dramatically reducing the amount of water lost to evaporation. Another unique thing about these cacti is that they only transpire at night time in order to reduce the water lost during the day. For those who may not know or forgot, like myself, transpiration is the “passage of water through a plant from the roots through the vascular system to the atmosphere,” which makes sense as to why it’s evolved to do it at night.
As far as coloration goes, these cacti are just a good old fashion green. They can be brighter green or darker depending on age and other factors but in general, they’re just green.
Height
As stated before, these cacti can become massive reaching upwards of 50 feet tall if left alone to grow. The rate at which they grow can change depending on how dry the climate is around them. In Arizona, Saguaro Cactus found in Tucson will grow nearly twice as fast as those found in western Arizona due to the annual precipitation differences between the two regions.
Once the seed starts to grow, the process to become a full-size cactus takes a long long time. After two years of growth, you can expect the cactus to only reach about 1/4 inch in height. If you see a cactus out in the wild that looks to be about a foot tall, just know that foot took around 10 years to achieve so be careful as to not ruin progress.
Leaves
Saguaro Cactus, like many other cactus, don’t have traditional leaves but instead, have spines and spikes. These spikes are used to protect the cactus from any animals or humans who are looking to tap into the cactus’s trunk. The spikes on Saguaro Cactus are extremely sharp and very strong to the point where people have found dead animals impaled on them, most notably a big horn sheep skull.
Besides the obvious protection aspect of the spikes, they provide a few other benefits to help the cactus survive the brutal desert. While one spike may not be enough to shade a plant, being covered in thousands of them kind of do the trick. Spikes tend to grow in clusters that are close to one another which provide just enough protection from the sun to help retain water.
The spikes on the Saguaro Cactus also help with water collection as well as disrupt airflow around the cactus preventing water from being carried away with the wind. The spike clusters help trap air close to the cactus while blocking a portion of new, hot air from coming in and drying out the plant.
Reproduction
Like most other plants, the Saguaro Cactus requires help from other animals and insects in order to reproduce and make seeds. Pollination of the cactus is done primarily by bats at night who seek out the flowers and their nectar that grow on top of the plant. During the day, pollination is carried out by insects like bees.
Once the cactus starts producing fruit, bats, cactus wrens, and even coyotes will eat the fruit that has either fallen or is perched atop the cactus and in turn, will carry thousands of seeds away from the cactus to be deposited somewhere else in the desert.
Flowers
Flowers for the Saguaro Cactus start to grow and bloom in April and will stay active until around June. If you want to see an open flower, be sure to go out either at sunset or early in the morning as the flowers close during the heat of the day for protection.
The flowers are white in color and have a waxy feel to them which I can only assume is because it helps with water retention much like the waxy outside of the cactus. If you see a bright red growth on the cactus, know that it means it’s been properly pollinated and is now growing fruit.
Seeds
The Seeds of the Saguaro Cactus are small and black and are primarily produced by the fruit in the thousands.
Range
Saguaro Cactus can be found in the Sonoran Desert which ranges from western Sonora Mexico all the way to western parts of Arizona. These cacti are picky about what elevations they grow at due to the fact that they are not suited to handle long periods of cold temperatures and frost. Because of this, you will not find Saguaro Cactus in the high deserts of Nevada, Utah, Colorado, or New Mexico. The furthest north these cacti will grow is around the Hualapai Mountains in Arizona.
There have been Saguaro Cactus found in southern California but for the most part, they grow in southern Arizona and Mexico.
Protection
While not endangered, Saguaro Cactus are protected in Arizona from destruction and harm. It is illegal to vandalize or damage the cactus in any way and you can be charged with a class four felony if you are found damaging these cactus. Special permits are also required to move or destroy a Saguaro Cactus do to how long they take to grow and how delicate they can be.
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References Used
- Wikipedia – Saguaro Cactus
- National Park Service – Saguaro Reproduction
- National Park Service – Saguaro Cactus
- https://www.desertmuseum.org/kids/oz/long-fact-sheets/Saguaro%20Cactus.php
- https://www.desertmuseum.org/kids/oz/long-fact-sheets/Flowers%20and%20Fruit.php
- https://www.plantsnap.com/blog/why-do-cacti-have-spines-4-reasons-cacti-are-spikey/
- https://www.pressconnects.com/story/news/local/2017/12/08/ask-scientist-why-does-cactus-have-needles/935726001/