Wallace Desert Gardens, Scottsdale, Arizona

     Being a botanist can make it difficult to get away from your home range during the growing season. This makes the late fall a perfect time to get away on vacation. This year, my girlfriend Susan Barry and I went on a trip to Arizona. We had a long list of proposed adventures and were anxious to get started experiencing them.
     My parents have a place in Scottsdale and we began learning the plants of the desert environment on a private tour of the Wallace Desert Garden. This site was previously owned by H.B. Wallace, a man from a very distinguished family that pioneered genetic seed modification and included a U.S. Vice-President and Secretary of Agriculture. As heirs of the family fortune, H.B. Wallace and his wife Jocelyn "created a spectacular 12-acre garden of arid land plants from across the globe."
     This site is confounded by a number of problems that threaten its long term existence, mainly that it resides within an affluent and gated community and tours are only available by reservation. My father arranged the tour after visiting with a group of friends who knew of the garden. It was a very neat place.

Wallace Desert Gardens, Scottsdale, AZ

     The tour proved to be a nice introduction to desert plants and although I was particularly interested in species native to Arizona (species we might observe in the wild later during our trip), we also learned about some interesting features of species that were planted there from other parts of the world.
     The term cactus refers to a group of dicotyledonous plants in the Cactaceae family.  All cacti are succulent plants, however not all succulent plants are species of cactus as I will explain later.  Also, all cacti are entirely New World in distribution with one exception. Rhipsalis braccifera occurs in Africa, Madagascar, and Sri Lanka in addition to both Americas.
     This is one of the most massive of the barrel cacti and perhaps the most abundant and widespread barrel cactus in Mexico. However, it is extremely slow growing and is endemic to Mexico so it is listed as "near threatened" by the IUCN.  Few young individuals can be found in the wild and its use in traditional candy threatens its longterm viability.

Barrel Cactus (Echinocactus platyacanthus)

    Creosote is a true desert shrub.  It occurs in three of the four major North American deserts (the Mojave, Sonoran, and Chihuahuan deserts).  The Great Basin desert is unlike the other three deserts and this shrub does not occur there.  It is believed to be one of the oldest living organisms on earth and true to its name, it smells like creosote.

Creosote Bush (Larrea tridentata)

     There are some plants that mimic cacti, that is, they look a lot like a cactus but they are not.  This phenomenon is called convergent evolution and the genus Euphorbia is a perfect example.  This group of plants did not evolve from the same common ancestor as the cactus group, but instead independently evolved similar characteristics, in this case, the succulent nature of the plant tissue that allows for the plant to survive in extremely arid conditions.

Resin Spurge (Euphorbia resinifera), from Morocco

       Our guide Lee pointed out this feature many times during our tour and it was especially prevalent in the cactus garden.  Before I mention why these particular plants were under a wooden structure perhaps you can figure it out on your own.  Hint:  There are plants in here from deserts all around the world.  

Cactus Garden

     Lee showed us many neat cactus species that have been planted within the building and some were quite large.  We were reminded though, that the Wallaces' planted all these species and so none of them had been there for more than 25 years.  Since they are from all over the world, many of them cannot survive the cold temperatures occasional to Arizona winters and with the large sliding windows and louvered ceiling, the plants are protected when temperatures drop below freezing.

Our guide Lee pointing out Opuntia alta

     This is a non-prickly Prickly Pear species called Opuntia tomentosa.  Tomentose is a type of pubescence, and refers to the dense and soft hairs that cover the pads (which are actually stems called cladodes).  This is one Prickly Pear you shouldn't be afraid to touch!

Prickly Pear Cactus (Opuntia tomentosa)

     Another cactus species was easy to identify by the chevron patterns on the trunk and I thought it was quite beautiful.

Chevron patterned cactus (Pachycereus pringlei)

     There were also a lot of Agave, Aloe, and Yucca species planted throughout the garden.  This one is called the Quiver Tree (Aloe dichotoma) because the leaves split in pairs.  It looks like an octopus!

Quiver Tree (Aloe dichotoma), from South Africa

     Another interesting group of cacti produce what is called a cephalium, which basically means "head."  When they are mature, they grow thick hair and from that flower and set seed.  It is essentially the equivalent of pubic hair for cacti!

Columnal Cactus (Espostoa lanata)

     This was a place where you had to watch very carefully where you walked and what you touched as many of the plants in the garden had sharp spines.  Spines are modified leaves or stipules borne from below the epidermis whereas thorns are modified stems with a sharp point.  Of course don't confuse either with prickles, which are outgrowths of epidermis or bark.  But what about bristles you might ask?!  Those are actually hairs (or hairlike structures)!  Clear as mud?

     Only once did I back into an Opuntia cactus while photographing and it sure did poke me good!  Susan also brushed by an Opuntia cactus and her leg had several fine hairs or bristles called glochids.  Anyone who has touched an Opunita pad knows about these!

     Spines assist in herbivore prevention and also aid in water loss by trapping air near the surface which reduces evaporation and transpiration.  The Dagger Cholla (Grusonia invicta) displays it best.

Dagger Cholla (Grusonia invicta)

     In the garden area where the barrel cacti were concentrated was a lovely Saguaro Cactus (Carnegiea gigantea) specimen.  The Saguaro is a tree-like cactus that is only found in the Sonoran Desert and is the state wildflower of Arizona.  It is also the largest cactus in the United States and can live up to 200 years. Young Saguaros cannot survive the intense heat of the desert, nor can they withstand trampling.  Thus, they grow under the shade and protection of a "nurse" plant like Palo Verde.

Saguaro cactus (Carnegiea gigantea) in the garden

Palo Verde (Cercidium floridum) with Saguaro cactus growing underneath

     On our way to the next area of the garden we stopped to look at this interesting cactus, a barrel cactus that had a funny scientific name, Ferocactus emoryi rectispinus!  Apparently this means you do not want to sit on it!

     Also called Compass Cactus, this species is drawn toward sunlight and this causes them to lean in a southerly direction.  You also do not want to cut barrel cacti open and drink the water inside because it is filled with alkaline juice instead of water.  Although it won't kill you, it will dehydrate you by forcing involuntary emergence of body fluids from both gastrointestinal directions.

Barrel Cactus (Ferocactus emoryi rectispinus)

     Another non-cactus succulent in the genus Stapelia was this carrion flower.  Like other carrion flowers, the flower is brown and low to the ground because it is pollinated by blow flies of the dipteran family Calliphoridae, which are attracted to the foul odor exuded by this plant, mimicking the odor of dead animals. 

Carrion flower (Stapelia hirsuta)

      Not a terrible backyard eh?!

Wallace Desert Garden, Scottsdale, AZ

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