Download Adaptations of Sonoran Desert Plants to Heat/Aridity There are three

Adaptations of Sonoran Desert Plants to Heat/Aridity
There are three main adaptive strategies of desert plants for surviving aridity:
Succulence
- succulent plants store water in fleshy leaves, stems, or roots in compounds or
cells from which it is not easily lost.
- they have extensive shallow root systems (< 4 in.) to take advantage of even
brief rainfall
- they have waxy cuticles on stems and leaves to reduce transpiration
- they have a reduced surface area - accomplished by having few leaves, no
leaves, or deciduous leaves
- they bind water in extracellular mucilage
- CAM photosynthesis - open stomates at night and then store CO2 as an acid
- cacti; agaves; euphorbias; elephant trees (Bursera)
Cactaceae (cactus family)
- 1800 spp., all but one of which are New World; 300 in Sonoran Desert
- flower must have many intergrading tepals, many stamens, and numerous
stigma lobes
- spines (specialized leaves) grow from cushionlike grayish pads called areoles
- pollinated by moths, birds, and bats, but primarily bees
- Sonoran Desert is home to four giant columnar cacti- 3 of which grow in AZ
Saguaro (Carnegiea gigantea) - largest cactus in U.S. (commonly 40')
-succulent stem is pleated with 12 to 25 ridges so cactus can take up water
-clusters of about 30 spines grow from roundish gray pads called areoles
spaced at 1 inch intervals along the ridges
-spines provide herbivore protection, shade, and slow dessicating winds
-saguaros are 90% water by weight and weighs 80 lbs per foot
-this large water content provides protection from temperature extremes
-13 to 20 well-developed woody ribs provide internal support
-pollinated by bees, doves, and bats
Organpipe (Stenocereus thurberi) - numerous columns rise from ground
level
-usually about 11 feet in height
-columns are pleated into 12 to 19 ridges
-frost-sensitive tropical plant; found only in far SW Az. and Northern
Mex.
-bat-pollinated
Senita (Lophocereus schotti) - same general form as organpipe
-differs by having fewer ridges (5to7)
-mature stems covered with long bristly gray spines
-found in AZ only in far SW in OPCNM
-very long-lived and bat-pollinated
Cardon (Pachycereus pringlei) - resembles the saguaro but thicker and
more stout
-not found in Arizona
-differs from the saguaro in height (commonly 60') and branching
(cardons branch closer to the ground and often have more arms)
-too cold in Az. for the cardon
-bat-pollinated
-NOT FOUND IN ARIZONA
Genus Echinocereus (Hedgehog Cacti)
-clusters of 1-foot tall stems
Genus Ferocactus (Barrel Cacti)
-globular unbranched stems ranging from 1-foot to 12-foot stems
-Ferocactos wislizeni (compass barrel) so called due to its noticeable
southward tilt due to better growing conditions to the shady north side of
the plant
-bee-pollinated
Genus Opuntia (chollas and prickly pears)
-stems are segmented, have tiny barbed spines, have tiny leaves on young
joints
-chollas even more drought resistant than prickly pears
-bee-pollinated
-reproduce mainly by asexual vegetative means - clones
-prickly pear keep stem joints vertical to minimize water loss
Agavaceae - 18 genera and 400 species
Genus Agave - leaf succulents
-40 species in the Sonoran desert
-most species live in semiarid, not arid, areas above the desert.
-most species a rosette of leaves
-reproduce by a flowering stalk at 10 to 30 years of age, then die
-provide food (roasted stems), rope fiber, medicine, and mescal
-Agave deserti is the most desert-adapted agave - shallow roots, root
growth occurs just after a rain, CAM plant, leaves channel rain to the roots
Genus Yucca - leaf semisucculent
-10 species in the Sonoran desert
-most species live in semiarid, not arid, areas above the desert
-most species a rosette of leaves
-unlike agaves, many species grow trunks
-reproduce by a flowering stalk, but more than once
-pollinated by moths
Euphorbiaceae (spurge family)
-8000 species worldwide
-many species are succulent and resemble cacti, particularly in Africa
-many euphorbs look like cacti because of convergent evolution, a process
which produces plants similar in outward appearance due to
similar environmental stresses
-recognized by their particular flower type
-Jatropha cardiophylla (limberbush)
-Pedilanthus macrocarpus (candelilla)
Drought Tolerance
- plants often appear to be a bunch of dried-up dead sticks.
- these plants have an ability to withstand extreme dessication.
- many nonsucculent plants can go for months without water.
- plants often shed leaves and enter a period of deep dormancy.
- brittlebush; bursage; creosote; ocotillo; calliandra
- Larrea tridentata (creosotebush)
- Most common shrub in Sonoran Desert
- Evergreen shrub 3 to 6 feet tall
- Most drought-tolerant perennial plant in N. America
- Can go 2 years without rain by losing leaves and even branches if
necessary, to save water
- Offsets clones from its root crown
Fabaceae (legume family)
-16000 species worldwide
-many are highly drought tolerant
-the following are all microphyllous (small leaves)
-the Sonoran Desert is characterized as a columnar cacti / legume desert
Genus Acacia (acacias)
- woody shrubs and small trees
Genus Cercidium (palo verdes)
- multi-trunked deciduous tree
- chlorophyll-containing green bark can carry out photosynthesis
- important nurse tree
- State tree
- yellow flowers
Genus Olneya (ironwood)
- tree up to 35 feet tall
- lavender flowers
- seeds eaten by many animals
- decreasing population due to cutting for charcoal
Genus Prosopis (mesquites)
- woody shrubs to 55 foot tall trees
- pods eaten by many large animals
- deepest known roots of any plant
Genus Calliandra (fairy dusters)
- 2 foot tall shrubs
Genus Caesalpinia (bird-of-paradise)
- shrubs or small trees
Genus Dalea (daleas)
- shrubs up to 3 feet tall
Drought Evasion
- annual plants which complete an entire life cycle during the brief wet season
and then set seed and die.
- their seeds then wait out the intervening dry period until the next rain brings
them to life. They can remain viable for decades.
- seeds are extremely hardy and have great resistance to environmental
extremes.
- desert annuals include wildflowers such as Mexican gold poppy; lupine, owl
clover, desert bluebells, penstemon, and a variety of mustards.
- winter-spring annuals; summer annuals; opportunistic annuals (Baileya)
- no annuals in polar zones or in tropics. Annuals increase with aridity - 1/2 of
Sonoran Desert plants are annuals and 90% are annuals near Yuma.
- spatial and temporal niche separation.
- some perennials evade drought by having underground parts that stay viable
during dry times and then send up stems, leaves, and flowers only in wet
times. Perennials of this type have fleshy roots, woody roots, or bulbs.
- threatened by alien invaders.
Other adaptive strategies include: microphylly (having small leaves), an adaptation to
avoid overheating; having leaves or stems of a light color; leaf orientation; selfshading. All these adaptations reduce the effects of intense light and heat. Light
coloring is often due to either waxy secretions or trichomes (hairlike scales).
Trichomes obvious on brittlebush and white bursage. Waxy cuticle obvious on
Agave deserti Verticals stems/leaves on jojoba and prickly pear.Self-shading is
displayed by many cacti - their spines shade the plant.