The large and impressive cacti that you can see all around the
Los Cabos area is the Cardón cactus (Pachycereus pringlei) which is the largest
cactus in the world.
There are about 1200 species of cactus, all of them native
to the Americas however the Cardón is 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. Slow growing plants and
extremely long-lived, many specimens live to well over 300 years.
''Cardo'' actually means ''thistle'' in Spanish, hence the
root of the name.
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. In many areas of the
Baja, 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 and 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 seeds will sprout only in warm
wet conditions following the tropical late summer rains or ''chubascos'', which
bring most of the seasonal precipitation to many of these desert regions and
germination is best when air temperature exceeds 40 C, but soil surface temperatures
remain under 70 C.
The Cardón 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. It needs no leaves and 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. 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 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, it 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. Flowers open in the
afternoon, stay open all night, then close about mid-morning 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 the 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 for 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. 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, the 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.