The Most Astonishing Boring Plant in the Mojave

It's the least interesting thing in this photo, and this was taken after a wet winter when it looks better than usual. Photo of Centennial Flat, CA by the author

There are a lot of dramatic and prominent plants in the California deserts -- towering Joshua trees, fierce bristling chollas, even saguaros along the Colorado River -- but one of the most amazing plants in the desert is one it could take you years to notice, hiding some jaw-dropping science behind a singularly unimpressive appearance.

Despite being part of the same botanical family as showier plants like roses, flowering plums and cherries, there is really nothing about blackbrush -- Coleogyne ramississima -- that commands your attention. Even in the rare very wet desert springs when it comes into full bloom, its flowers are pallid yellow, pretty close up but unremarkable from even a short distance, and generally hidden behind a haze of grayish branches when other shrubs are bright spots of glorious color.

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Most of the time, blackbrush is so unobtrusive it can make other unobtrusive plants seem gaudy. The plant gets its common name from its overall color; in dense stands, it can make whole hillsides look funereal, dark gray summer leaves and stems only a little lighter. It ranges throughout the desert Southwest, thriving best at elevations between 2,000-5,000 feet, and in areas especially conducive to its growth it can reach a height of five feet. In the California desert it rarely tops three feet, and you might be hard-pressed to find an individual plant wider than that.

But it can be hard to pick out an individual plant, as blackbrush tends over time to form a patchy cover over the desert soil. I first noticed the plant when negotiating those patches hiking off-trail in the Mojave: clear corridors through the blackbrush would fork, twist, and suddenly end in cul-de-sacs, and I often walked three times the actual map distance just in all the retracing of my steps I needed to do to get from Point A to Point B. I once tried to just push on through, and was immediately repulsed by a few dozen sharp, thorn-like ends of stems. It's formidable, and that was when I started to want to know more about the species.

I said above that blackbrush "tends over time" to form a cover, but it can take a while to fill in. A very long while, in fact. It takes a wet winter and spring to bring blackbrush into bloom. Even in a good bloom year the plant doesn't produce a whole lot of its tiny seeds, and of those seeds very few escape the local rodent and bird populations. If a seed lands in a good spot to germinate and remains uneaten, an unlikely event in a habitat where animals search constantly for every available bit of food, then a subsequent winter and spring may provide just the right combination of moisture and temperature to bring that seed to life -- at which point it is even more vulnerable to marauding animals.

A once-a-decade bloom in Hidden Valley, Joshua Tree NP | Creative Commons photo by Brent Miller

In practice, this means that Coleogyne never reproduces from seed unless the desert gets two relatively wet winters in a row, which rarely happens. Fortunately, each plant lives a long time -- 400 years or more by some estimates. A plant need only have one of its offspring survive to maturity in that time to maintain the local population numbers. If two survive in 400 years, on average, then the blackbrush's tribe increases.

And yet it's not hard, once you start noticing blackbrush, to see that in a lot of places it forms nearly solid stands, carpets of dormant summer gray covering many miles of open desert. These stands are crucial parts of the desert biome. Blackbrush is hard for people to hike through, and it's just as hard for non-human hikers to penetrate. This means that other plants' seeds -- Joshua tree, Mojave yucca, cacti of various kinds, the occasional piñon or juniper -- find blackbrush "forests" a congenial place to germinate and grow for a few years. Blackbrush thus acts as a "nurse plant" to many other, more noticable desert species. Without blackbrush cover, we'd have a lot fewer picturesque succulents out there.

Given that blackbrush reproduces very slowly, you might reasonably start to wonder how long it took for the species to cover, say, the alluvial fan at Red Rock Canyon near Las Vegas, or the uplands of the Wee Thump Wilderness or any of the hundreds of other places in undeveloped sections of the Mojave where blackbrush blankets the land.

Researchers Robert H. Webb, John W. Steiger, and Raymond M. Turner looked into just that question, and in a 1987 paper entitled Dynamics of Mojave Desert Shrub Assemblages in the Panamint Mountains, California, they reported that it takes a very long time indeed. The researchers studied a number of disturbed areas in the above-named mountain range along Death Valley's western margin, and measured the rate of regrowth of various desert shrubs in each of the areas. Some of the areas had been disturbed by mining and other human activities in the 19th and 20th centuries; some had been disturbed by landslides and other natural phenomena thousands of years ago. Webb, Steiger and Turner concluded that in some areas, the length of time needed for blackbrush to cover one fifth of an area could be as long as -- in their words -- "tens of thousands of years."

Think about that length of time needed to cover just 20 percent of a stretch of land, and then consider the fact that many places in the desert have upwards of 60 percent blackbrush cover. I don't usually repurpose my previous writing here, but I'm having trouble coming up with a better way to express this than in a passage I wrote on Coleogyne on my website a couple years ago, so begging the readers' forgiveness, this is what that study means:

Find the oldest coast redwood forest on earth, with trees three hundred feet tall and thirty feet thick at the base, some of them 2,000 years old. Then plat out a few square miles of the White Mountains's bristlecone pine groves, home of the Methuselah tree and its ancient cohort, ranging up to twice as old as the redwoods. Then pick a random piece of Cima Dome, a couple miles in each direction, full of unprepossessing blackbrush.

Chainsaw all three. Bulldoze it all flat. Leave only stumps flush with the ground. Then let them all grow back at their own pace. When the new redwoods and bristlecones are considerably older than the ancient ones we have now, the blackbrush may still not be more than about halfway recovered.

That's still optimistic, though. As we mess with the climate, the desert is expected to get hotter and drier, on average, meaning that the likelihood of getting two consecutive winters wet enough to prompt Coleogyne reproduction will change. In the meantime, we are destroying broad swaths of blackbrush habitat through urban and suburban development, razing the desert for energy extraction, deliberate and accidental fire, and a whole host of other activities. Revegetating an area in blackbrush requires that a few old, established plants remain to repopulate the earth, and so between making the desert drier and completely denuding square miles of it at a time we are, most likely, ending the ancient blackbrush forest's existence.

An ancient forest is what it is, after all, especially from the point of view of the packrats and kangaroo rats and night lizards that inhabit it. The blackbrush forest has been there for tens of thousands of years, feeding and sheltering unimaginable thousands of generations of their forebears.

You know what they say about a little knowledge. Since learning this little bit about blackbrush a couple of years ago, I can't see that solid, drab, literally monotonous gray shroud on the desert landscape without a sharp intake of breath, a tingling awe running up the back of my neck, a wonder of nature only made more wonderful by how well it's hidden.

And if we lose it, we might just lose much of the rest of the desert as well.

About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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