Cacti and Desert Succulents

Fantastic Cacti

The cacti of Saguaro National Park are a diverse group of plants, ranging from the tiny fishhook pincushion to the massive and majestic saguaro. Not only does the Sonoran Desert offer an amazing variety of cactus species, it also exhibits some of the most fascinating adaptations in the plant world. Adaptations are what enable the cactus plants to thrive under harsh conditions of desert: extreme heat, nearly constant sun, and scarity of water throughout most of the year.

 

Adaptations

Adaptations are what enable the cacti you see all around you to thrive under the harsh conditions of the Sonoran Desert. Plants must adapt to the extreme heat, constant sun and scarce water, or they will die.

 

Teddybear cholla is found throughout both districts of the park. Don't let its name fool you, though! This cactus is not cuddly.

NPS Photo / T. Wiewel

Spines

The most conspicuous adaptation of the cactus family is the spines, which are modified leaves. In addition to protecting the plant from hungry or thirsty animals, spines provide shade during hot summer days and warmth on cold winter nights. Spines also help prevent water loss that occurs due to dry winds.

On cholla cacti, which are often called "jumping cactus" the spines also play a major role in reproduction. Cholla are segmented cacti; the plants are made up of many segments, which are loosely attached to the preceeding segment. Additionally, each spine is covered with a thin sheath, which separates from the spines quite easily. When an animal accidentally brushes against the cactus, the sharp spines stick into its skin and the segment breaks off of the parent plant. The segment may travel with the animal for a few minutes or hours. Eventually, the spines slip from their sheaths, and the segment falls to the ground. If soil conditions are right, the segment may take root and grow into a new plant. This process can be painful: one meaning of cholla is "sore."

Roots and Stems

As with most desert plants, cacti have a shallow root system. These shallow roots enable cacti to capture the rainwater from even the lightest showers.

If you take a close look at a saguaro or barrel cactus, you will notice a series of distinct accordion-like pleats on the outside of the plant. These pleats allow the plant to expand while it is absorbing rainwater and to shrink when it is using its stores of water. Without the pleats, damage would certainly occur to the plant's skin. Even so, a saguaro may take in more water than its pleats will allow (cacti cannot stop drinking!) When this happens, the skin breaks open into a long wound. Although the plant usually forms scar tissue over the opening, it can be a vector for bacterial infection, just like a cut on your skin.

Growth

As with most plants, cacti make their food through a process called photosynthesis. However, unlike most plants that only take in carbon dioxide during the day, cacti utilize a complex form of carbon dioxide fixation known as Crassulacean Acid Metabolism, or CAM. This method reduces the amount of water lost to the atmosphere because the pores on the plant's skin (called stomata) open only at night when desert temperatures are lower and humidities are higher.

After absorbing the carbon dioxide, it is changed into other compounds, largely malic acid, to be stored at night. The next day, the sunlight completes the formation of plant sugars through photosynthesis. Because the liquids in a cactus are so rich in organic acids, the water stored inside is not fit to drink. Old movies that show the thirsty Westerner cutting open a barrel cactus to extract handfuls of clear, cold water are just Hollywood fantasy. Always carry water!

 

 

Saguaro National Park Cactus List

Walk the cactus garden at either visitor center to find signs identifying native desert plants. The Valley View trail in the Tucson Mountain District (west) and the Freeman Homestead trail in the Rincon Mountain District (east) also have identification signs. Park gift shops carry a number of identification guides. A book specific to our many species of cacti is "Cactus of Arizona Field Guide" by Nora & Rick Bowers and Stan Tekiela, Adventure Publications, 2008.

The list below includes the 28 species of cactus found growing wild in Saguaro National Park. The list does not include named varieties or subspecies.

Common Name	Species Name	Blooming Season	Park District	Notes
Saguaro	Carnegiea gigantea	May	Both	Don't miss this one!
Organpipe Cactus	Cereus thurberi	June	West	One known specimen
Beehive Cactus	Escobaria vivipara	March - July	East	Uncommon
Queen of the Night	Peniocereus greggi	June	Both	Easily overlooked
Scarlet Hedgehog	Echinocereus coccineus	May - July	East	Compare to Claret Cup
Pink Hedgehog	Echinocereus fendleri	March - July	Both	Aka: Strawberry Hedgehog
Rainbow Cactus	Echinocereus rigidissimus	April - May	East	Mid elevations
Claret Cup Cactus	Echinocereus triglochidiatus	May - August	Both	Mid to high elevations
California Barrel	Ferocactus cylindraceus	April - September	West	Aka: Fire Barrel
Fishhook Barrel	Ferocactus wislizenii	July - September	Both	Common; yellow fruits
Fishhook Pincushion	Mammillaria grahamii	March - September	Both	Bloom after rains
MacDougal Pincushion	Mammillaria heyerdi	April - May	East	Flattened shape
Thornber Pincushion	Mammillaria thornberi	April - September	West	Rare; in sandy soils
Green-flower Pincushion	Mammillaria viridiflora	April - May	Both	Grassland species
Pencil Cholla	Opuntia arbuscula	May	Both	Hybridizes with others
Buckhorn Cholla	Opuntia acanthocarpa	April - May	West	Purple cholla
Teddy Bear Cholla	Opuntia bigelovii	April	Both	Likes rocky slopes
Chain Fruit Cholla	Opuntia fulgida	June - July	Both	Likes bajada and flats
Christmas Cholla	Opuntia leptocaulis	April - May	Both	Low ground cover
Staghorn Cholla	Opuntia versicolor	April	Both	Purple cholla
Cane Cholla	Opuntia spinosior	April - June	Both	Mid elevations
Pancake Prickly Pear	Opuntia chlorotica	April - June	Both	Mid elevations
Engelmann Prickly Pear	Opuntia engelmannii	April	Both	Hybridizes
Prickly Pear	Opuntia phaecantha	April	Both	Hybridizes
Beavertail Prickly Pear	Opuntia basilaris	May	East	Escaped from gardens
Cow-tongue Prickly Pear	Opuntia lindheimerii	April - May	Both	Invasive from gardens
Indian Fig	Opuntia ficus-indica	April - May	East	Invasive from gardens
Purple Prickly Pear	Opuntia santa-rita	April	West	Escaped from gardens

 

While these cactus are beautiful, the pain of the spines will make you want to keep your distance!

NPS photo / T. Wiewel

Play it Safe with Spines

Cacti are armed with an assortment of sharp spines. They vary from tiny, hair-like glochids to large, curving hooks to 3-inch spears. Whichever type you bump into, spines can pose a painful hazard to the unwary desert enthusiast.

The most frequently encountered cactus in the park is one of the 7 varieties of cholla. While extremely painful to remove, cholla and other cactus spines are not poisonous.

To remove a cholla segment, slide a pocket comb between the cactus and your skin. Once the comb is held securely under the segment, a quick, firm flick will usually dislodge it. A pair of tweezers or pliers may be needed to remove any spines or spine sheaths left behind. The tiny brown glochids at the edge of prickly pear spines are very difficult to remove—sometimes, a piece of duct tape applied to these will pull them out. Wash with soap and water afterwards and monitor the area like you would any break in the skin.

Join us in keeping our cactus safe, too! Report any poaching you see, purchase landscape plants at a licensed nursery, and please do not collect cactus. Spines don't deter collectors, but visitor tips can help stop "cactus rustling" in the park.