|Pachycereus pringlei in Baja California, Mexico|
(S.Watson) Britton & Rose
Pachycereus pringlei, also known as Mexican giant cardon or elephant cactus, is a species of cactus native to northwestern Mexico in the states of Baja California, Baja California Sur, and Sonora. It is commonly known as cardón, a name derived from the Spanish word cardo, meaning "thistle."
Large stands of these magnificent cactus still exist, but many have been destroyed as land has been cleared for cultivation in Sonora.
A symbiotic relationship with bacterial and fungal colonies on its roots allows P. pringlei to grow on bare rock even where no soil is available at all, as the bacteria can fix nitrogen from the air and break down the rock to produce nutrients. The cactus even packages symbiotic bacteria in with its seeds.
Cardon is the tallest cactus species in the world, with a maximum recorded height of 19.2 m (63 ft), with a stout trunk up to 1 m (3.3 ft) in diameter bearing several erect branches. In overall appearance, it resembles the related saguaro (Carnegiea gigantea), but differs in:
- fewer ribs on the stems
- more heavily branched
- branching occurs nearer the base of the stem
- areoles and spination differ
- the location of the blossoms, lower along the stem
- fruit heavily spiny
Its flowers are white, large, nocturnal, and appear along the ribs as opposed to only apices of the stems.
Lifespan and growth
An average mature cardon may reach a height of 10 m, but individuals as tall as 18 m are known.  It is a slow-growing plant  with a lifespan measured in hundreds of years, but growth can be significantly enhanced in its initial stages by inoculation with plant growth-promoting bacteria such as Azospirillum sp.  Most adult cardon have several side branches that may be as massive as the trunk. The resulting tree may attain a weight of 25 tons. 
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