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Botany Ecology

The Saguaro Cactus Life Cycle: step-by-step guide with pictures!

Some saguaro cacti live for 200 years or longer! Saguaros grow very slowly. The speed of growth depends on many factors such as precipitation, temperature, and soil quality. Let’s explore the saguaro cactus life cycle in five steps! Notice that desert animals play a key role in two of these steps.

1. Germination

Saguaro cactus seedling

A seed germinates. The two cotyledons open to form a tiny plant. Seeds that germinate in shady areas such as beneath palo verde trees are most likely to survive through the fragile young stages and reach maturity.

The seedling cactus grows through its first summer and develops more areoles and spines. At just a few millimeters in height, the seedling is so small that it can be difficult to spot.

2. Maturity

It may take ~35 years for a saguaro cactus to reach maturity and produce its first flowers.

The rate of growth depends on environmental conditions such as precipitation, temperature, soil quality, and the type of cactus. For saguaro cacti, growth happens very slowly over many years.

When a cactus reaches reproductive maturity, it can produce its own flowers. Time to reach maturity depends on the cactus species. For example, the saguaro cactus takes several decades to reach maturity.

3. Flowering & Pollination

The lesser long-nosed bat is a nighttime pollinator of the saguaro cactus

The cactus flowers bloom. Cactus flowers make tasty nectar to attract pollinators like bats, bees, and doves. Pollen is transferred between plants by the pollinators. This is a type of symbiotic relationship called mutualism because both the pollinator and the plant benefit. The pollinator gets a tasty meal of nectar, and the plant gets pollinated.

4. Fruiting

Saguaro fruits are a food source for many animals in the Sonoran desert. People sometimes eat the fruit too.

Once pollinated, the cactus fruit begins forming from the ovary of the flower. Cacti can produce huge amounts of fruit. For example, a single saguaro cactus may produce upwards of 100 fruits each year. That’s a lot of fruit! The ripened fruit splits open, revealing sweet flesh and seeds.  This sends the signal to animals that the fruit is ready to eat!

5. Seed Dispersal

When an animal eats the saguaro fruit, it ingests some seeds. The seeds are then dispersed in the animal’s scat.

Desert animals like birds, coyotes, and tortoises eat cacti fruit and disperse seeds in their scat. This is another example of a mutualistic relationship between an animal and a cactus. The animal gets a meal of fruit and the cactus gets its seeds dispersed. If the cactus is lucky, some of its seeds will be deposited in locations with good growing conditions. Over its lifespan, a single saguaro may produce millions of seeds. However, only a few of those seeds will germinate, grow, and reach maturity.

Classroom cactus life cycle materials:

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References and Further Reading

  1. Ceotto, E. (2009). Cultivation of Carnegiea gigantea from seeds: a journey in desert ecology. Desert Plants25(1), 10. Available: https://repository.arizona.edu/bitstream/handle/10150/556548/dp_25_01-010-015.pdf?sequence=1
  2. Dimmitt, M. (n.d.). Cactaceae (cactus family). Arizona-Sonora Desert Museum. Available: https://www.desertmuseum.org/books/nhsd_cactus_.php
  3. Helmy, Olga. 2021. Carnegiea gigantea, saguaro. In: Fire Effects Information System, (Online). U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Missoula Fire Sciences Laboratory (Producer). Available: www.fs.usda.gov/database/feis/plants/cactus/cargig/all.html
  4. National Park Service (n.d.). The Saguaro Cactus (Carnegiea gigantea). Organ Pipe Cactus National Monument. Available: https://www.nps.gov/orpi/learn/nature/saguaro-cactus.htm
  5. National Park Service (2017). How Saguaros Grow. Saguaro National Park. Available: https://www.nps.gov/sagu/learn/nature/how-saguaros-grow.htm

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