Pleuraphis rigida: knitting the desert together

More wash Left: Big galleta fills a wash in the Southern California portion of the Sonoran Desert.

[A preview of a piece I wrote for El Paisano, the newsletter of the Desert Protective Council.]

In April, Desert Protective Council staff and several colleagues undertook a brief survey of the site of the proposed Solar Two project near Ocotillo, CA. The project would obliterate a wonderful and largely intact swath of Colorado desert alluvial fan and wash habitat, with smoketrees and ancient creosote, and the DPC opposes the project for that and other reasons. A brief description of the trip can be found on our Desert Blog.

One of the most striking aspects of the Solar Two site was the site’s thriving, indeed almost exuberant stands of big galleta, a large bunchgrass native to the arid southwest.

Big galleta (Pleuraphis rigida, formerly Hilaria rigida) is a perennial grass, one of three species of Pleuraphis, the others being James galleta and tobosagrass (P. jamesii and P. mutica, respectively.) Among the genus Pleuraphis’ closest relatives are the desert bunchgrass genera Dasyochloa and Erioneuron, commonly referred to as the woolygrasses, and the odd Munroa squarrosa, also called false buffalograss. Under ideal conditions Pleuraphis rigida grows three to five feet tall, its clumps getting just as wide over time. It tends to thrive best below 5,000 feet in elevation in gravelly or sandy soil with excellent drainage, not doing nearly as well on clay soils. After it’s established it can achieve considerable age. One rephotography study near the Grand Canyon found that some individual clumps of big galleta lived for at least 120 years.

Like many native bunchgrasses, big galleta is an important primary producer in the desert food chain. It’s preferred browse for desert bighorn, and other animals from muledeer to pronghorn to jackrabbits eat their share of big galleta as well. Big galleta doesn’t set a lot of seed, and as a result is not of major importance as a food source for strictly graminivorous animals. Some habitual seed-eaters like the kangaroo rat do take advantage of big galleta’s lush green matter, and in any case thick stands of the grass do provide excellent cover for small animals, seed-eaters included.

In parts of the desert with both winter and monsoon rainy seasons, big galleta will go through two yearly growth periods. Big galleta begins flowering in late winter throughout its range, and responds enthusiastically to summer precipitation, often putting out new flowers and setting seed in a remarkably short time. In one California study, a stand of big galleta responded to a monsoonal storm on August 11 by flowering on August 30, with seed maturing by mid-September. Big galleta is well-equipped to take advantage of even a little precipitation. Of all desert plants, big galleta is one of the most adept at extracting water from the soil, and its efficient “C4” metabolism allows the plant to photosynthesize without losing much water to transpiration. Its root system can extend for many yards beyond the boundaries of the clump, and as a result big galleta effectively stabilizes desert soils, holding down dunes, in effect knitting the desert together.

That seed set doesn’t tend to result in a flush of big galleta seedlings. Seedling establishment is actually quite rare for the species: it may take 20–40 years for a stand of galleta to begin to revegetate a disturbed area, whether that disturbance is artificial or the result of a landslide, flash flood or other natural phenomenon.

The established clumps of big galleta do help other seedlings gain a foothold in the desert, however. Their dense hearts can provide effective nurseries for young cholla, protecting the cacti in their earliest, most vulnerable growth stages. Once a cholla has gotten itself established and outgrown its galleta grass nursery, its stems may help protect the bunchgrass from being eaten by larger herbivores. Pleuraphis rigida has also been found to provide nurse-plant services to barrel cacti and desert agave, and as a common understory plant in Joshua tree forests big galleta very likely harbors the occasional young Joshua as well.

Those larger succulents are often what comes to mind when someone thinks of desert plants, and rightly so: they are beautiful, unique, and well-adapted to their surroundings. Even veteran desert rats might pass by a healthy stand of big galleta without paying it mind. Pleuraphis rigida is a fascinating and beautiful plant and deserves a place in any desert fanatic’s list of favorites, but whether we notice it or not it will keep on doing what it does best: feeding animals, tending seedlings, and knitting the desert together.

4 thoughts on “Pleuraphis rigida: knitting the desert together

  1. Laura Cunningham

    Very good article, we need more fans of the desert grasses, those underappreciated yet ecologically crucial plants. I was just at the Calico site today, where the solar company seeking to destroy those Pleuraphis stands wants to similarly scrape our big galleta east of Barstow, as you know.

    The monsoon was building up to the south and cumulus over Hector Road, but the galleta was all dry here, waiting for the late summer rains to green up.

  2. Sven DiMillo

    Once i was collecting plant samples in the Ivanpah Valley a week after a summer rain, and I was rustling down to the center of a galleta bunch to get at the new green shoots; during a pause I heard some rustling and 10 feet away was a female tortoise doing exactly the same thing.

  3. arvind

    I love the image of a biological layer knitting together the underlying geological layer. Now instead of “the” web of life, I’m imagining several layers of webs knitting each other together with living ones like bacterial and multi-cellular as well as non-living ones like the terrestrial, aquatic and atmospheric environments.

  4. Bill

    Nice post Chris.  As an ecologist I love to learn about the linkages between plants, animals, and soil. 

    I see ecological relationships as a tapestry where some parts are “knitted” together and other parts are not.

    Of course, as always, I really liked your presentation as far as the writing is concerned.

    Thanks.

    Bill:www.wildramblings.com