Monday, June 12, 2017


Photo by Marty Horowitz 5/31/2017

Click on the photo for a larger view of Creosote (Larrea tridentata). Note the white fruits [fruit = thing with the seed(s)] with the darker seeds showing through in the centers.

Some interesting info on creosote from the Desert Museum in this article:

There is a legend that creosotes inhibit growth of any other plants around them. Not exactly. The roots will excrete a substance which inhibits growth of bursage, its main competitor, and it will also inhibit germination of its own seeds so competing new creosote bushes will not grow nearby. But, the creosote is an important nurse plant for small cacti and many other plants.

And even more interesting science from the Joshua Tree National Park site:

Although creosote bushes produce large numbers of fuzzy seeds at each flowering, few of them are able to germinate. It takes decades for creosote bushes to return to areas that have been cleared of native shrubs. Even a one-foot high plant is probably at least ten years old. As the shrub grows, branches continue to originate around the periphery of the original stem crown. The branches grow upward for about six feet giving the whole shrub the rounded shape of an upside down cone.
As growth continues, the oldest branches gradually die and the stem crown splits into separate crowns. This happens at an age of 30 to 90 years. Eventually, the original stem and early branches die and rot away; the connections between adjoining segments of the stem crown thus disappear. The plant has now become a clone, composed of several independent stem crowns all descended from one seedling. The process continues until the clone spreads across the ground in a circular or elliptical shape.

Although the creosote in the Sonoran Desert is older that that of the Mojave, the creosote from the Chihuahuan Desert is the oldest, i.e., closest to the common ancestor. (Also from this Joshua Tree site.)

Actually, what botanists classify as a single species in the North American deserts is now known to consist of three genetically different shrubs. Creosote bushes of the Mojave Desert have 78 chromosomes, those of the Sonoran Desert (southern Arizona) have 52 chromosomes, while those of west Texas (Chihuahuan Desert) have only 26. Such an increase in the number of chromosomes in plant evolution is not that unusual. Seedless watermelons, for example, were the result of doubling the number of chromosomes of regular watermelons, the lack of seeds being a side effect. In the case of the Mojave creosote, the increase in chromosome number may have been accompanied by an increasing ability to survive on the less summer rainfall in the Mojave.

Whenever you're out and about, take a closer look at this fascinating plant!

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