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.
“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. ]
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| 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.
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
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