San Felipe's Cardon Cactus

San Felipe, Baja, Mexico

San Felipe is home to the cardón cactus (Pachycereus pringlei), the world’s largest cactus. There are about 1200 species of cactus, all of them native to the Americas. The cardón is nearly endemic to the deserts of the Baja California peninsula. Some of the largest cardones have been measured at nearly 21 meters (70 feet) high and weigh up to 25 tons. These very slow growing plants are also extremely long-lived, and many specimens live well over 300 years.

San Felipe Desert Cardon
Desert Cardón

“Cardo” means “thistle” in Spanish. It is said that when Hernando Cortés attempted to establish a settlement in Baja in 1535, the many spiny cacti earned it the name “Isla de Cardón”, because at the time, they believed the peninsula was an island. In Latin, “pachy” means thick and “cereus” means waxy. One has only to see the thick arms of this pale gray-green, waxy skinned cactus to understand what the traveling American botanist, Cyrus Pringle, meant when he named the species.

Many first time visitors to Baja mistake this giant cactus for the ecologically similar saguaro cactus (Carnegiea gigantea), another inhabitant of the Sonoran Desert. However, the saguaro does not live in Baja and while there are a few stands of cardón found across the Gulf of California on the Mexican mainland, they seldom occur near the saguaro.

The Sonoran Desert in Baja California can be divided into distinct sub-regions: the San Felipe, Vizcaíno, Magdalena, and Gulf Coast Deserts. The cardón has adapted to all of these sub-regions and is also found in the tropical dry forests of the Cape. In many of these areas, the cardón is the predominant plant, and may be found growing in large tracts of forest. These large stands of the tall columnar cacti are called “cardonales”.

The cardón grows best in the deeper soil of the alluvial fans of arroyos and other waterways. The cardón can be found between sea level and about 950 meters (3200 feet) in elevation from near El Rosario in the north, to the tropical Cape region at the southern tip. The cardón occupies only the relatively frost free regions of the Baja deserts, being confined by the freezing temperatures to the areas of Baja south of 31.2ºN.

The seeds of the cardón will sprout only in the warm wet conditions following the tropical late summer rains or “chubascos”, which bring most of the seasonal precipitation to many of these desert regions. Another factor limiting geographical distribution is that germination of seeds is best when air temperature exceeds 40ºC, but soil surface temperatures remain under 70ºC. The cardón has adapted to the arid conditions of the Sonoran Desert as many cacti have. It has a columnar form to present greater surface area to the morning and evening sunlight, and less to the harsh sun of midday. The branching pattern of the arms maximizes the efficient capture of solar radiation.

The cardón needs no leaves – it is a true “cladophyll” – a plant that performs photosynthesis through its skin, rather than through leaves. Modified epidermal cells in the skin of the stems, called “chlorenchyma” do the work of converting sunlight to energy. Water loss during photosynthesis is reduced through crassulacean acid metabolism (CAM), a method of photosynthesis that the cardón shares with many of the cacti and succulents that inhabit the dry areas of the world. The stomata on these plants open only after dark, allowing the cactus to absorb carbon dioxide during the cooler night hours, making these plants very water efficient.

The main trunk of the cardón may have as many as 25 vertical branches, up to 1.5 meters (5 feet) in diameter. In older plants the branches are usually taller than the trunk. The cardón are especially spiny when they are smaller, to protect them from predators. As they grow older, many of the spines fall off and are not replaced. The lower trunks of older plants turn gray, and a cracked, woody bark makes them look like the thick legs of an elephant. Woody vertical ribs allow the columnar cactus to expand and contract like an accordion, storing the water it needs to survive in the arid conditions. These cacti have developed extensive, shallow root systems which quickly capture the brief, but torrential rains of the region.

A large cardón may store over a ton of water in the fleshy, pulp-like tissues of its trunk. In order to support this great weight, the large cactus has an interior framework of hardwood vertical rods, lightweight, yet extremely strong, which act to stiffen the ribs. This amazingly tough hardwood skeleton has allowed the cardón to become the largest cactus species, able to thrive in the very harsh climate of the Baja California's Sonoran Desert. From March through June, flowers appear on the upper tips of stems, especially stems with warm, southern exposure. ]

Cardon buds ready to open.
Cardón buds ready to open.

Flowers open in the afternoon, stay open all night, then close about midmorning the next day. The reason for this, is that the cardón, like most of the other columnar cacti of the southwestern corner of North America, depends on nightly visits from nectar feeding bats for pollination. Several studies have shown the importance of the nectar feeding bats to the reproductive processes of he columnar cacti stands of the Southwest. For most of these cacti, including the cardón, bats are the primary pollinator, with almost no viable seed production occurring from birds, insects, or any daytime visitor. Cacti that depend upon these bats for pollination usually produce light, or white colored flowers, with a deep-throated, bell shape.

Flowers are located on the upper portion of the plant and remain open only one night. They also produce copious amounts of nectar, a distinctive odor to attract bats, and a thick layer of pollen that coats the rim of the flower. The lesser long nosed bat (Leptonycteris curasoae) spends its winters in southern Mexico. Its annual migration northward is timed to coincide with the flowering of the columnar cacti and agaves of the Sonoran Desert.

Peak nectar production times for cardones are between 8:00 and 10:00 p.m. Later in the night, bats visit the cardón, circling a cactus several times in wide loops, then hovering in front of an individual open blossom. The bat thrusts its head down into the bell shaped tube of the flower, lapping the nectar from the tube with its long tongue. The large amount of pollen on the rim and sides of the tube sticks readily to the fur of the bat’s face and head. The actual feeding visit lasts less than a second.

When the bat visits the flower on another plant, cross pollination occurs. The return migration of the lesser long nosed bat south from the deserts of Arizona in the late summer is during the cardón's fruiting period. The bats feast on the ripe cactus fruit, helping to spread the seeds.

Many types of birds also feed on the fruit of the cardón, which is about 5 cm. in diameter (around the size of a golf ball) and has short, golden, fuzzy spines all over the outside. The ripe fruit often splits, revealing the sweet, red flesh. Each fruit contains about 800 black seeds which are consumed along with the flesh by the bats and birds. This is also crucial to the successful growth of the cardón.

The long nose bat.
Long-nose bat.

For best germination, the seeds need several conditions, which the birds and bats help to bring about. Cardón seeds need to be “scarified”, or have their skins roughed up before they will crack and sprout. The digestive juices in the stomach of the consumer does this job perfectly. Another requirement for the successful growth of a juvenile cardón is a “nurse” plant. To grow successfully, he seed must become established under another plant or shrub, which protects the young cactus from the full brunt of the sun, as well as predation. Birds and bats eat the seeds, then fly off to roost in a tree, depositing the scarified seeds with their droppings into the nurse plants below, to await the warm rains of wet summer.

In the best of conditions, thousands of seeds must germinate to produce one cactus, as conditions are extreme and foragers are eager to eat the tiny plant. Growth of these seedlings is extremely slow, less than 2.5 cm. per year, and it may take decades for them to grow large enough to emerge from beneath the nurse shrub. The main threats to the mature cardón are overgrazing by cattle, clear cutting by humans, and a little understood disease, called “flat top decay” which causes the withering of the top of the cactus. The disease is not widespread, and does not currently appear to threaten the cactus population.

The cardón, like the other columnar cacti of the Sonoran Desert, has survived the harsh, arid conditions for thousands of years by its ability to adapt. Future studies may use genetic markers to further study the pollination and breeding structure of this cactus, and its ecological interdependence with the lesser long nosed bat. These studies may be crucial to the successful survival of many species of desert cacti, and even the Sonoran Desert ecosystem itself.

Article written by Bob Chamlee