Saturday, August 30, 2003 By Michael Plagens PHOENIX ----- PHOENIX ----- Ocotillos are among the most distinctive and characteristic plants of the Southwestern USA deserts. They are distributed widely from the Chihuahuan Desert of Texas, through the Sonoran Desert of Arizona and on into the Mojave Desert of California. Their success is due to three important desert adaptations. Back to Sonoran Desert Naturalist Home Page © Michael J. Plagens, 1997-2003
Vol. 5 No. 15
Ocotillos
Regreen
Sonoran Desert Sciences
First, the insides of the branches and the short basal trunk have within a spongy and highly water absorbant woody material that can soak in and hold indefinately a lot of water. When sporadic rains fall, the ocotillo's roots, likely aided by symbiotic soil fungi, quickly bring in enough water to store in these tissues for later use.
Second, the leaves of ocotillo are small so that their surface area to volume ratio is high. This frequent trait of desert plants helps keep the leaves from being overheated; cooler leaves loose less water.
Finally when water becomes scarce, but before the ocotillo has exhausted it's supplies of stored water the leaves wither, yellow and fall off, leaving naked stems that conduct only minimal photosynthesis. Thus the ocotillo saves enough water to survive until the next rare rainfall. When it rains again this strategy of retaining some water pays off by giving the ocotillo a head start on regreening and activating root tissues for water uptake. Peak flowering can occur at the proper time of year, regardless of the preceeding rain history. Ocotillos can put on a new flush of leaves three or more times per year.
August 2003's monsoon rains have been spotty, but have allowed ocotillos to green up and begin photosynthesizing.
With recent summer monsoon rains this group of ocotillos have flushed new leaves. Some are even blooming, contrary to the usual March to April typical bloom period. This group of ocotillos have grown up among the tailings of an old exploratory mine shaft at Piestewa (Squaw) Peak in Phoenix. Photo taken Aug 24, 2003.
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