San Francisco State University
Geography 316: Biogeography
The Biogeography of Cereus giganteus
by Alexandria Gross, student in Geography 316, Fall 1999
Kingdom: Plant
Phylum:
Class:
Order: Cactales
Family: Cactaceae
Genus: Cereus
Species: Cereus giganteus
Description of Species
The saguaro cactus comes from the family Cactaceae; its order
Cactales, the genre name is Cereus, and its species the Cereus giganteus. Further
discussion on the taxonomy of the saguaro will be discussed in the family tree line
section. In 1908 in honor of Andrew Carnegie, the species name was changed to Carnegiea
gigantean (Klaus, 1997). Other common names for it are sahuaro and pitahaya (Klaus,
1997). The first description of the Saguaro was in 1848, describing it as a
particular species with a huge columnar, candelabra shaped cactus growing to 18 meters in
height, a diameter of 65 cm, and living as long as 200 years (Klaus, 1997) The plant has
12-24 ribs, with brown areoles; which are axillariy buds that immediately produces a
cluster of spine primordial (Gibson and Nobel, 1986), spaced every 2cm. The spines are
brown, 7 mm long and up to 12 are arranged radially per areole, with 3-6 of these being
center spines. (Klaus, 1997)
The saguaro is native to Arizona, southeastern California and
the Sonoran Desert in Mexico. These particular biomes are extremely hot in temperature,
which serves as an ideal environment for this plant, which is able to store and hold water
for periods of time. The saguaro can also tolerate temperatures to well below
freezing. (Gibson and Nobel, 1986.)
The Saguaro is the state flower for Arizona, the fruit in
which its produces is said to be edible and bright in color (Klaus, 1997). It
is also held in high esteem by the Papago Indians in the Sonoran Desert because the fruit
of this cactus is valued as food staple. The juice of the plant is fermented and used in
celebrations.
I had the opportunity to see these beautiful plants during my stay
in Tucson, Arizona this past year. I am glad to have the opportunity to present a
descriptive analysis on such an interesting species as the Cereus giganteus (saguaro).
This paper will examine the saguaro’s history, its habitat and other pertinent
information such as its evolution and distribution.
Habitat
The favorable environment for the saguaro cactus is described
as rocky or gravelly soils located throughout the foothills, and canyons. The elevation is
600 to 3,600 feet elevation. The saguaro is generally located on the south-facing
slopes where it is protected from the winter cold. (Benson, 1969) The altitude tends to be
less on the western edge of the distribution area; also rainfall in this area is less than
five inches yearly, due to low rainfall saguaros are normally situated in the drainage
channels. (Benson, 1969) Benson also states that anchorage is important to the saguaro
survival where strong winds are common during the raining season causing the soil to
become soft, when the soil is no longer hard enough to support the gigantic cactus, which
weighs a ton than the strong winds are capable of blowing the cactus over.
Natural History
Like humans, other biological species have a family tree, which can
help in explaining their existence; this section should give you a general sense of the
saguaro’s family tree line. As mentioned in the introductory, the saguaro comes from
the Cactaceae family, generally described by Britton and Rose 1963 as perennial, succulent
plants with spiny organs name areoles. Another physical characteristic that the
author’s mention is that the Cactaceae are usually leafless with a few exceptions
being the pereskia and perskiopis species, which are actually in the Pereskieae family,
they possess large, flat, fleshy leaves. They also mention that the spines vary in size,
form, arrangement and color depending on the species type; the areoles of the saguaro are
situated in the axils (the upper angle between leaf and stem). Some of the areoles bear
flowers, spines. These are some of the predominate characteristic of the Cereeae family
(Gibson and Nobel, 1986). Areoles of the saguaro also possess various seeds and, or
berried fruits.
The Cactaceae is broken into three tribes: Pereskieae,
Opuntieae and the Cereeae. The saguaro is a biological descendant from the Cereeae family.
The specific characteristics that defines the Cereeae tribe per Britton and Rose (1963) is
that the areoles are without glochids (short, very thin, deciduous spine that has barbs
and is easily dislodged from the areole; a characteristic found in the Opuntioideae
family) (Gibson and Nobel, 1986); they are without leaves except the species member
cotyledonary; and the flowers have definite tubes (Britton and Rose, 1963) Other physical
characteristics mentioned by Britton and Rose (1963) that help to identify a Cereeae are
that its members are less fleshy, terrestrial, simple, much branch and many-jointed. The
joints are said to be globular, oblong, cylindrical, columnar or flattened; the spines,
usually present, are described as various in color and arrangement and size. The berries
that the Cereeae yields is said to be fleshy; and its’ small seeds are usually brown
or black with a thin testa (the hard covering of a seed; a seed coat) (Britton and Rose,
1963) (Gibson and Nobel 1986).
The sub tribe of the Cereeae is the Cereanae, which characterizes
this group as possessing erect, bushy, sometimes diffuse, stout or slender cacti.
Britton and Rose (1963) group the known species into 38 different types of genera, with
the Carnegiea identified as part of this cluster. This particular offspring of the cacti
sub tribe, Cereanae Carnegiea is exclusively described as gigantic, columnar cacti; scales
of flower narrow. Let’s take a look at the natural habitat in which the saguaro calls
home in order to shed some light on its evolutional distribution.
Evolution
When researching the cacti’s evolution or ancestry, some
questions an evolutionist may ask is: Did the plant live in desert? Did it have spines and
areoles? Was it a CAM plant? (Gibson and Noel, 1986) The ancestral plant is said to have
been the Pereskia. The original plant, pereskia resembles a leafy shrub or tree because of
its woody appearance. Evidence of this was found in a wood skeleton that consisted
of a solid cylinder without conspicuous, unlignful primary rays, and a number of holes
(rays) eventually evolved. (Gibson and Noel, 1986) The anatomy of the ancestral plant was
short stalk of leaves defined as petioles and a single, ovate blade with entire margins.
The leaves consisted of minor veins that diverge in a parallel fashion from a central mid
vein, identified as pinnate venation. The leaf blade had stomates on both side of the
leaf. Thos area was considered to be the photosynthesis organ of the plant. The stem
was identified as cylindrical and relatively thin. (Gibson and Noel, 1986)
Unlike the present day cacti, this ancestral plant was a C3.
During the dry seasons for the short tree forest, where the ancestral plant resided,
droughts forces the cacti to loose it leaves (deciduous), but when the leaves fully
expanded, they flower. The reproductive structure for the flower of the cacti was
produced from a newly formed areole (An axillary bud that immediately produces a cluster
of spine primordial), which produces only one flower at a time. (Gibson and Noel,
1986)
The plant order from the cactaceae comes from is called the
Centrosperm family. Invented in 1876 by August W. Eichler, a German taxonomist, he
identified the centrosperm members by their derived characteristics of containing a
campylotropus, nucellus, ovules with two integuments, hypodermal archesporial.
Plygonum-type embryo sac, pollen grains and a persiperm. (Gibson and Noel, 1986)
Other families that have been study and proven to have evolved from
the centrosperm order are: Achatocarpacae (achatocarpus family), Aizoaceae (ice
plant family) Amaranthaceae (amaranth family), Basellaceae (basella family, Chenopodiaceae
(goosefoot family), Didiereceae (didierea family), Halophytaceae (halophytum family),
Molluginaceae (carpet-weed family) and the Nyctaginaceae (four-o’clock family).
(Gibson and Noel, 1986)
Distribution
In order to understand how the saguaro has made desert environments
located throughout the southwestern United States and Mexico its home; a historical
general overview on the cacti geographic origin must be examine. Secondly, a look at the
distribution patterns could give some insight on explaining the saguaro’s existence
in areas such as Arizona (see map below), southeastern California, and Sonora, Mexico.
Historically, there is very little actual information on the geographical or geological
events responsible for the creation of the Cactaceae family. (Gibson and Nobel, 1986)
However, there is some indication that that cacti is a product of disjunct distribution of
some plant group affected by the separation of Africa and South America, some 125 millions
years ago (Gibson and Nobel, 1986). A cacti plant, Rhipasali was studied by Alfred Wegner,
a German meteorologist who discovered that this plant had existed both in Africa and South
America. He used to help in explaining his continental drift theory. Conversely, other
arguments were used to discredit his theory; another hypothesis introduced was that birds
from the Old World spread the seeds into the New World, by way of their feces. Another
geographical location mentioned when trying to describe the origins of the cacti has been
the West Indies where some of the more primitive species have also been found. For the
most part, the Cereea sub tribe is said to have evolved primarily in the eastern South
America, especially in Brazil.
Now lets take look at the environment, which is not only
suitable for the saguaro but generally for all of its cacti related members. The desert is
defined as an area or biome where the average rainfall is no more than 25 cm per year, the
temperature during the day ranges anywhere from 35 o –130 o F. Vegetation is said to
be sparse due to the fact that sand and barren rocks predominantly fill the desert. Desert
soils have been identified entisols (soils lacking horizons, usually because their parent
material has accumulated only recently) and aridisols (soils of dry climates, low in
organic matter, and often having subsurface horizons of accumulation of carbonate minerals
or soluble salts) (Holzman, 1999; Strahler and Straler) The only type of plants or
vegetation that can withstand such a poor soil conditions are thorny bushes, or any flora
possessing either a shallow root or long tap roots such as shrubs or succulents. (Holzman,
1999) The physical survival mechanism for the succulent plant is its ability to store
water, allowing it to survive through long periods of drought (Gibson and Nobel, 1986). In
regards to animals only reptiles such as lizards, toads and snakes, along with rodents,
owls, vultures and insects are able to survive under such harsh environment. (Holzman,
1999.) Geographically, deserts can be found in the southwest United States, the Great
Basin of North America, Northern Mexico, areas in the Middle East and Africa.
General Characteristics
The saguaro lives in deserts and semiarid habitats where rainfall is
low, causing the soil to remain dry throughout the year. The saguaro relies on its water
reserves to get it through the long droughts. (Gibson and Noel, 1986) The stem of the
cactus holds about 90 to 94% of water, causing the appearance of swollen ribs (a vertical
or nearly vertical ridge that is formed on the side of a stem by the outward displacement
of the tubercles) and tubercles (an enlarged, succulent projection on a stem; in cacti, a
modified lead base) (Gibson and Noel, 1986) Water is lost through the surface (stem)
by transpiration, the ribs and tubercles flatten and collapse on themselves creating
narrow valleys and crinkled surface appearance. (Gibson and Noel, 1986)
The general reproductive structures of the saguaro are typical
of its family, the cactaceae. (Gibson and Noel, 1986) The cactaceae flower possesses
an inferior ovary (female structure), which is below the other major structures of the
reproductive system such as the stamen, floral tube, style, nectary chamber, pines and
stigma lobes. (Gibson and Noel, 1986) Inside of the flowers is hundreds of white, pollen
bearing stamens (see picture below). When the flower opens, which occurs at night,
it tends to attract bats. The flower remains open attracting the day creatures such as
bees and hummingbirds. The saguaro flower also bears fruit berries, which split open; the
seed are a reddish black. (Gibson and Noel, 1986)
Works Cited
Internet Reference:
Klaus, Trenary http://www.herbal-shaman.com/
Version 2.2, (12-27-97)
Academic:
Britton, N.L. and Rose, J.N. 1963 The Cactaceae. New York, New
York.
Dover Publications
Gibson, Arthur and Nobel, Park S. 1986. The Cactus Primer.
Cambridge Mass.
Harvard
University Press
Benson, Lyman 1969 The Cacti of Arizona. Tucson, Arizona
University of Arizona Press
Cox, C. Barry and Moore, Peter D. 1993 Osney Oxford England
Blackwell Science Ltd.
Lecture:
Holzman, Barbara Fall 1999 Biogeography Class Biomes Sheet
send comments tobholzman@sfsu.edu
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