‘I’m too thorny for my leaves….’

28 Jan

Allthorn (Koeberlinia spinosa)

Another plant of many common names is one that sticks out like a sore thumb. Literally.

Found mostly in the Chihuahuan Desert area of Texas, New Mexico and Mexico, the Allthorn seems to diverge from many common assumptions. Although known by several common names –Crown of Thorns, the Crucifixion thorn, Junco, and Allthorn- this thorny shrub, Koeberlinia spinosa, won’t be confused with any other once encountered.

Allthorn (Koeberlinia spinosa) Winter, 2014.

Taxonomists also seemed baffled by this perennial shrub. The althorn plant stands alone: it is the only species in its genus (Koeberlinia), which is the only genus in the entire family, Koeberliniaceae (Allthorn, or Junco, Family).

Typically growing up to 10 feet or more and with many branches going in all directions, its most noteworthy character is the long, thick and dark green spines.  What most people don’t realize, however, is those sharp spines are actually stems.  Tiny and scale-like Allthorn leaves appear shortly after a rain on the spiny stems and dropping off within a few days after rains cease.  Likewise, the small greenish-white flowers appearing in March through October, also in response to rains, grow in inconspicuous clusters. The one-quarter inch shiny black berries, on the other hand, are obvious against the dark green stems and favored by birds, although some herbivores may feed on very young stems.

Allthorn stems

Allthorn stems

The Allthorn is similar in some respect to the well-known ocotillo, the tall whip-like thorny stems growing from a single base at the ground. Both shrubs are perfect examples of adaptation to the desert environment: they leaf out in response to moisture in the air and drop their leaves shortly thereafter. Additionally, they are somewhat an oddity in the plant physiology world. Although both shrubs have transient small leaves, their green bark and stems contribute to their food supply by a rather unique ‘hybrid’ of two photosynthetic pathways. Although this process is less efficient for food production, it does reduce water loss by transpiration, which is higher in leaves than in the plants’ green stems.

In contrast to the ocotillo, which has shallow roots, the Allthorn has an additional survival mechanism: its roots reach into the soil both at shallow and deep levels to reach water. Older wood turns woody and dark brownish gray, which helps protect the trunk of the shrub, and the branches tangle and twist to form an impenetrable barrier to humans and animals alike.

The Allthorn is very drought and cold hardy, surviving temperatures to 0 degrees F, and prefers full sun. Specimens of this shrub were first found and characterized by a German naturalist, Wilhelm Freiberr Karwinsky, in Mexico around 1830. The plant, including family and genus, was named in the honor of a German clergyman and botanist C.L. Koeberlin, by Karwinsky.

Allthorn shrub in winter.

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