Why saguaros have pleats

The saturated desert floor can become very soft after a heavy rainstorm, sometimes making it difficult for a heavy saguaro to remain standing in the wind.
Wide reaching, but shallow roots can lead to saguaro blowover

L. Bolyard

The roots of a saguaro grow out from the plant in a radial fashion, several inches under the ground. During a heavy rain, a saguaro will absorb as much water as its root system allows.
The flesh of a saguaro cactus is spongy, thready, and similar to tough squash.
The flesh of the saguaro cactus is located just beneath the tough green skin.

L. Bolyard

To accomodate this potentially large influx of water, the pleats allow the flesh to soak up water, expanding like an accordion. Conversely, when the desert is dry, the saguaro uses its stored water and the pleats contract.
Saguaro cactus skeleton showing through tear where arm broke off.
A bloated saguaro's arm became too heavy after a rainstorm and the following high winds, leaving the woody skeleton of the saguaro cactus visible through the exposed flesh.

L. Bolyard

Because the majority of a saguaro is made up of water, an adult plant may weigh 6 tons or more. This tremendous weight is supported by a circular skeleton of inter-connected, woody ribs. The number of ribs inside the plant correspond to the number of pleats on the outside of the plant. As the saguaro grows, the ribs will occasionally fork and the corresponding pleat will also fork at the same place.

Sometimes saguaros have the chance to soak up a larger than usual amount of water - such as after a large summer rainstorm. The ground can become very soft after such a storm and with the added weight of the new water, the heavy cactus sometimes fall over or lose an arm.

Saguaro cactus ribs protruding out of broken saguaro that fell after a monsoon storm.
A look inside a broken saguaro reveals the different layers of the cactus.

L. Bolyard

Layers of a saguaro:

protective spines

epidermis (green part)

cortex or pulp

ribs (with corresponding pleat on surface)

pith (inside the ribs)

Last updated: February 24, 2015

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