Organ Pipe Cactus

Stenocereus thurberi

Photo © by Michael Plagens

This mature Organ Pipe Cactus was photographed at Organ Pipe National Monument, Arizona, USA.

photo by Michale Plagens

This photograph was taken at Organ Pipe National Monument in May 2006 and is also available on hosted at Wikipedia.

BRANCHING: This cactus is easily recognized by the dozen or more columnar branches rising from a very short trunk and the virtual lack of branching above the ground.

SPINES: Approximately fifteen straight spines per ariole, 13 mm long, dark gray and all about the same thickness.

FLOWERS: The large, mostly white flowers, which are tapered basally and give a tubular appearance, open at night to be visited by nectar-feeding bats and hawk moths. The petals are numerous and waxy-white.

FRUIT: Behind the dense coat of spines that eventually fall off is a tasty, red fruit or pitahaya as it is called in northwestern Mexico.

RANGE: Common at Organ Pipe National Monument and north to near Ajo, Arizona. Extremely rare beyond this range in Arizona. Widespread in Sonora, Mexico.

Like the saguaro, the developing flower buds are very attractive to ants, wasps and flies. The night-time guard over the developing buds and fruit is taken on by formidable Camponotus (Tanaemyrmex) acutirostris Wheeler ants. Not only are these ants much larger, but they can also discharge formic acid at any disturbing force. The ants, like the other insects that come to cactus buds appear to remove a sticky substance, possibly a sugar.

Cactaceae -- Cactus Family

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Camponotas festinatus on Organ Pipe Cactus, photo © by Michael Plagens

A pair of carpenter ants (Camponotus ocreatus) photographed at night at Organ Pipe Cactus National Monument on Organ Pipe Cactus. May 2013. The red buds secrete sugary substances that feeds the ants and gives them reason to defend the plant against herbivores.

More Information:

Sonoran Desert Field Guide
Sonoran Desert Places
Sonoran Desert Naturalist Home Page


Copyright Michael J. Plagens, page created 29 Mar. 2007,
updated 18 July 2019.