Xeric environments (Ancient Greek ξηρός ksēros, “dry”), or desert-like environments, are some of the most extreme locations in which plants can be found.  Plants must possess exceptional adaptations in order to survive  with minimal water under intense solar radiation.

The most intriguing aspect of xeric species is their similar appearances, even when two species are unrelated and separated by thousands of miles.  Most xeric plants have a succulent-like growth habit; waxy on the outer surface with water rich tissues inside the leaves and stems, to prevent water loss.  Many xeric plants have also developed either C4 or CAM photosynthesis to better conserve water, differing from C3 photosynthesis, exhibited by the majority of plants not living in desert-like conditions.  Overall, most xeric plants resemble each other superficially, but with a trained eye, most families are quite distinguishable.  This is why xeric plants serve as a prime example of Convergent Evolution.

The best-known xeric plant is the cactus, in the family Cactaceae.  Cacti perform CAM photosynthesis and are characterized by their strange shapes and prickly thorns.  But not all plants that fit this very basic description are cacti!

Here’s a better way to narrow down if you are actually looking at a cactus:

  1. Thorns will appear in whorled clusters called areoles.  These spikes are actually modified leaves that are used for protection rather than photosynthesis.  In cacti, leaves can serve a different purpose as the photosynthetic tissue (green tissue) is along the stems and branches of most cacti species.
  2. Flowers are usually very colorful (red, yellow, pink, etc.), have many petals, and many anthers surrounding the flower center.
  3. If damaged, the cacti will exude a clear jelly-like sap.
  4. Cacti grow natively in the western hemisphere in the United States, Mexico, Central America and northern South America.  (The one exception to this geographic rule is the genus Rhipsalis.  In addition to being found in the New World tropics, some species are native to tropical Africa, Madagascar, and Sri Lanka, probably transported by migrating birds.)


    • Cactaceae
    • Pseudopilocereus azureus

    • Photo Credit: Jenny Gordon
    • Cactaceae

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Lophocereus schotti

    • Photo Credit: Jacob Golan
    • Cactaceae
    • Carnegia gigantea

    • Photo Credit: Jacob Golan
    • Cactaceae
    • Cleistocactus straussii

    • Photo Credit: Jacob Golan
    • Cactaceae
    • Aporocactus flagelliformis

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Echinopsis sp.

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Aporocactus flagelliformis

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Rhipsalis baccifera

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Rhipsalis elliptica

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Rhipsalis warmingiana

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Rhipsalis tucamanensis

    • Photo Credit: Jenny Gordon
    • Cactaceae
    • Rhipsalis pentaptera

    • Photo Credit: Jacob Golan
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The most easily confused plants with cacti are the xeric adapted plants of the Euphorbiaceae family.  Desert adapted  plants in the family perform CAM photosynthesis and resemble cacti by also having strange shapes and thorns.  Here is how to tell if a desert plant is in the Euphorbiaceae family.

  1. Thorns appear in clusters of two, with green leaves sometimes appearing at the same spot.  Like cacti, these thorns are modified leaves.
  2. Flowers are usually unisexual, male or female.  This means a single flower will have either carpels or stamens, but both types of flowers appear on the same plant.  The family Euphorbiaceae also has a cyanthium, or pseudoanthium, flower structure in which the reproductive structures resemble an oval or sphere that hangs from the end of the reproductive branch and is surrounded by pedal-like bracts.
  3. If damaged, the plant exudes a white sap. 
  4. Euphorbiaceae is not an exclusively xeric family and species occur throughout the world.  However, xeric adapted Euphorbiaceae are native to Africa. 

    • Euphorbiaceae
    • Euphorbia confinalis ssp. rhodesica

    • Photo Credit: Jacob Golan
    • Euphorbiaceae
    • Euphorbia lactea

    • Photo Credit: Jacob Golan
    • Euphorbiaceae
    • Euphorbia obesa

    • Photo Credit: Jenny Gordon
    • Euphorbiaceae
    • Euphorbia obesa

    • Photo Credit: Jenny Gordon
    • Euphorbiaceae
    • Euphorbia grandicornis

    • Photo Credit: Jacob Golan
    • Euphorbiaceae
    • Euphorbia echinus

    • Photo Credit: Jacob Golan
    • Euphorbiaceae
    • Jatropha integrolia

    • Photo Credit: Jacob Golan
    • Euphorbaceae
    • Euphorbia horombensis

    • Photo Credit: Jacob Golan
    • Euphorbiaceae
    • Jatropha integrolia

    • Photo Credit: Jacob Golan
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Although the families Cactaceae and Euphorbiaceae are the most commonly confused, there are additional xeric species that are just as easy to confuse.

The Didiereaceae family looks just like the typical xeric plant and even uses CAM photosynthesis.  The Didiereaceae family has the following characteristics:

  1. Thorns appear one at a time surrounding the stem or branch.  Unlike Cactaceae and Euphorbiaceae, Didiereaceae thorns are not derived from modified leaves.  Under proper seasonal conditions, small leaves grow through the greyish outer bark to perform photosynthesis.
  2. Didiereaceae is a small family endemic to Madagascar.

    • Didiereaceae
    • Alluaudia adscendens

    • Photo Credit: Jenny Gordon
    • Didiereaceae
    • Didierea madagascariensis

    • Photo Credit: Jenny Gordon
    • Didiereaceae
    • Alluadia adscendens

    • Photo Credit: Jenny Gordon
    • Didiereaceae
    • Alluaudia adscendens

    • Photo Credit: Jacob Golan
    • Didiereaceae
    • Alluadia adscendens

    • Photo Credit: Jenny Gordon
    • Didiereaceae
    • Alluaudia procera

    • Photo Credit: Jacob Golan
    • Didiereaceae
    • Alluadianopsis fiherensis

    • Photo Credit: Jenny Gordon
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The Fouquieriaceae family has a similar xeric habitat but performs normal C3 photosynthesis.  Fouquieriaceae:

  1. Have long weak thorns.  Under favorbale condition, leaves grow and die, leaving behind a hardened petiole, which becomes a "thorn".
  2. These plants are only found in Southern California and Baja Mexico.

    • Fouquieriaceae
    • Fouquieria splendens

    • Photo Credit: Jenny Gordon
    • Fouquieriaceae
    • Fouquieria burragei

    • Photo Credit: Jenny Gordon
    • Fouquieriaceae
    • Fouquieria fasciculate

    • Photo Credit: Jenny Gordon
    • Fouquieriaceae
    • Fouquieria peninsularis

    • Photo Credit: Jacob Golan
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Other xeric plants that may be confused with other xeric plants:

Agave is in the family Asparagaceae.  Thorns can be found in some species at the tip or along the edge of the large leaves.  Tequila is made from Agave tequilana.


    • Asparagaceae
    • Agave salmiana

    • Photo Credit: Jenny Gordon
    • Asparagaceae
    • Agave cv. variagata

    • Photo Credit: Jacob Golan
    • Asparagaceae
    •  Agave salmiana

    • Asparagaceae
    • Agave multifillifera

    • Photo Credit: Jenny Gordon
    • Asparagaceae
    • Agave ocahul

    • Photo Credit: Jenny Gordon
    • Asparagaceae
    • Agave ocahul

    • Photo Credit: Jacob Golan
    • Asparagaceae
    • Agave filifera

    • Photo Credit: Jacob Golan
    • Asparagaceae
    • Agave cv. variagata

    • Photo Credit: Jenny Gordon
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Pachypodium is a genus in the Apocynaceae family, or milkweed family.  This strange genus resembles a cactus but is native to Madagascar.


    • Apocynaceae
    • Pachypodium lamerei

    • Photo Credit: Jacob Golan
    • Apocynaceae
    • Pachypodium lamerei

    • Photo Credit: Jenny Gordon
    • Apocynaceae
    • Pachypodium geayi

    • Photo Credit: Jenny Gordon
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This desert dwelling plant is actually a Gymnosperm!  It is called Welwitschia miarbilis (Welwitschiaceae) and grows only in the Namib Desert.


    • Welwitschiaceae
    • Welwitschia mirabalis

    • Photo Credit: Jacob Golan
    • Welwitschiaceae
    • Welwitschia mirabalis

    •  Welwitschiaceae
    • Welwitschia mirabalis 

    • Photo Credit: Jacob Golan
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Check out other xeric families: Crassulaceae, Asparagaceae


Page by Jacob Golan 

 
  • Equisetaceae
  • Fabaceae
  • Commeliniaceae
  • Ericaceae
  • Araceae
  • Begoniaceae
  • Araceae
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