Xerophyte

Trunk

Erect, well-formed to 60 cm in diameter, enlarged at the base and vividly suggesting the leg of an elephant. On the trunks of old trees, a smooth grey bark replaces the green surface and there is little or no indication of the ribs, which have been flattened by the secondary thickening.

Central Spines

1-3, greyish white with darker tips, to 3 cm long.

Roots

The root systems is relatively shallow but extend laterally for distances of 20 meters or more. A symbiotic relationship with bacterial and fungal colonies on its roots allows Pachicereus pringlei to grow on bare rock even where there is no soil 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.

Flowers

Arising from the areoles just below the apex of the stem down to 30 or 40 cm from the apex, opening both at night and during the day, funnelform to bell shaped, white, to 8 cm long; pericarpels and floral tubes bearing small scales with masses of brown hairs arising from their axils.

Ribs

10-16, at first deep, but become more shallow with increasing age. The glaucous green of the surface is marked by faint dark lines which run from the bottom of the groove to the apex of the ridge. The accordion-like vertical ribs enable Pachycereus stems to expand as moisture is absorbed and to contract as it is used, moreove they helps to scatter solar radiation.

Stem

Strongly fluted, blue-green to dark green, becoming yellow-green,20-40 cm in diameter. Higher on the old plants a rough bark is formed on the branches too, gradually extending down from the tops of the ribs.

Fruits

globose, somewhat dry at maturity, to 7 cm long, covered with yellowish brown felt and bristle and contains about 500 very small seeds, a large number of which are abortive.

Habit

Plants treelike, columnar, branched from near the base to 2-3 m above ground. Young plants of Pachyrereus Pringlei are slender at the base for many years, but increase greatly in thickness after formation of branches begins. In favourable situations the plants often reach a height of 10-12 m and produce from 5 or 6 to as many as 30 branches. It is only rarely that the Pachyrereus Pringlei retains an upright posture with all its branches in erect position. They usually give the impression of having been vigorously battered by the wind and thrown out of balance by their great weight.

Note

Pachyrereus pringlei and saguaro (Carnegiea giganteaSN|6374]]SN|6374]]), the two largest cacti in the Sonoran Desert, often occur together in western Sonora, but the two can be readily distinguished at a distance. Pachyrereus pringlei is a stouter, more massive plant that branches closer to the ground and the branches are inserted at a sharp angle rather than a sweeping curve. Saguaros has more numerous (19-25) vertical ribs and generally initiate branches higher off the ground and the mature stems are green rather than glaucous. The features of germination and growth are much like those in Carnegiea so far as is known and the young plants may be difficult to distinguish.

Blooming Season

Spring ( late March or early April).

Radial Spines

7-10, whitish to greyish-black, to 2 cm long. Flowering areoles large, terminal, covered with brown felt, connected by furrows or confluent.

Areoles

In young plants the ribs are capped by a close-set series of areoles with white glochids.