Monocot Week Part 4: Yucca Trees, Misadventure and a Video

Re-reading my previous post, it occurs to me that a reader (if anyone actually ever read this blog) could be perhaps justified in accusing me of a bit of hyperbole. For by any objective, utilitarian measure, the “Best Monocot Ever” would probably more realistically be something like wheat, or rice, or corn, which of course have fed countless billions and been the foundation of dozens of civilizations over the past 10,000 years, as opposed to my nominee- the Joshua Tree- which with the exception of the now-extinct giant sloth, has never fed anything that stood on two legs.

But hyperbole aside, The Joshua Tree, Yucca brevifolia, is hands-down the weirdest-looking tree in North America. This thing is so freaky-bizarre it looks like something out of a Dr. Suess book. Like palm trees, Joshua trees are monocot trees that independently evolved a wood structure totally alien to the standard wood architecture of conifers and dicots. Joshua trees are actually yuccas, and are therefore fairly closely related to… asparagus. They’re the only yucca to have evolved into a real tree. Unlike Palm trees, of which there are over 2600 different species on 6 continents, there’s only 1 species of Joshua tree, and it lives only in a pretty small area of the Southwest US, specifically within the Mojave Desert.

Tangent - Subspecies: The one species of Joshua Tree is actually divided into 2 subspecies. The version that occurs in Southern Nevada and extreme Southwestern Utah is Yucca brevifolia jaegeriana. Everything I saw last week was jaegeriana. The version in Southern California and Northwest Arizona(?) is Yucca brevifolia brevifoliia. There’s one significant difference: brevifolia is bigger, which is why the most impressive Joshua trees are in California, in places like Joshua Tree National Monument.

Actually, some of the most impressive Joshua trees I’ve seen are those lining the main downtown drag of the town of Yucca Valley, CA. I’m sure they enjoy far more moisture than a typical “wild” Joshua, and they’re positively stately as a result.

In fact it really only occurs at some of the higher elevations around the edges of the Mojave; down in the low (~3,000 ft) Mojave basins, it’s absent, and occurs more often on the sloping “uplands” and bajadas leading to mountain ranges. The greater precipitation and well-draining soils of these settings better meet its higher moisture requirements. So while it’s often thought of as a classic Mojave plant, it’s really more of a fringe player today.

Tangent – Prehistoric Range: What’s interesting about its range though, is that it seems pretty likely that within the last 30,000 years, during the last Ice Age, it was far more widespread, occupying many of the lower basins. And some of the best evidence for this comes from ancient dung, specifically the dung of the extinct Giant Ground Sloth. The Giant Ground Sloth went extinct at least 9,000 years ago. In the Gypsum Cave, in Clark County, NV, South of I-15, scientists in the early 1930’s found hair bones and dung of the Giant Ground Sloth. The dung showed that a majority of their diet was Joshua Tree leaves. Yet today Joshua Trees occur nowhere near low-elevation (2,000 ft) Gypsum Cave.

In this respect the Joshua Tree reminds me of the Giant Sequoias or Coast Redwoods: trees that until recently (the last 15,000 – 20,000 years or so) occupied a far greater range than the present, and I wonder if we’re seeing these amazing trees in their last millennia.

The structure of Joshua tree wood is not only alien to the Standard Wood Architecture, but to the architecture of Palms as well, having evolved along a completely independent evolutionary path. Unlike Palms, they branch, and unlike Palms, the trunks undergo secondary thickening, though through a completely different, separately-evolved mechanism than in conifers or dicots, and without a continuous layer of cambium.

Wherein I Conduct An Experiment

So I read about the unique structure of Joshua wood prior to Monocot Week and was curious about it, so I collected a limb on my trip, and when I returned home, examined a cross-section of Joshua wood next to a similar-sized cross-section of dicot wood (specifically Bigtooth Maple, Acer grandidentatum.) You can see the clear difference in the photo below. The Joshua wood (left) is lower-density, softer and lighter. It lacks any kind of growth rings, and the interior, where heartwood or sapwood should be, is filled with a tough, fibrous pulp, which is surprisingly tough and difficult to break without a saw or blade.

(Actually, I guess this was more of an “observation” than an “experiment”. Kind of an experiment in the way that making toast is kind of like “cooking”…)

So when I went to Vegas, I planned to do most of my close-up Joshua Tree observing in Cottonwood Valley, Southwest of the city and up against the Spring Mountains, which separate Las Vegas from Pahrump Valley. I’d biked there several times 8-10 years ago and remembered fondly the Joshua Tree woodlands. But when I returned, I found that most of Cottonwood Valley- over 33,000 acres- burned in a huge fire in 2005, and today the dead Joshuas far outnumber the living. It was still beautiful, but a bit disappointing.

But as it turned out I later ended up traveling through a beautiful, Joshua-filled basin, mainly as a result of my final day of Monocot week, a (mis)adventure I think of as…

The Mormon Mountains Adventure/Fiasco

I had one more adventure planned for Monocot Week: to hike Mormon Peak, the 7,400 ft high point of the Mormon Mountains, which lie North of I-15, between Vegas and Mesquite

Tangent: In February 2001 I climber Moapa Peak, (View from peak pictured right), the prominent peak on the Southern end of the range, and it was a spectacular climb, with a hairy knife-edge traverse to a fantastic summit.

What attracted me to Mormon Peak wasn’t just the peak, but the rumor of another stand of relic Ponderosa, similar to- but more isolated, more remote (~30 miles from the nearest such trees) and fewer (maybe a dozen trees)- than the relic stand on Little Creek Mountain.

Tangent: More than a “rumor, actually- I’d confirmed it, via this photo I found on the web, taken by a hiker to the summit in 2003. He wasn’t looking for the stand, but his photo captures it, to the left of the ridge below in the foreground…

I’d obtained directions from Brian Beffort’s hiking guide: Afoot & Afield in Las Vegas and Southern Nevada. The access involves a ~20 mile drive along the RR tracks up Meadow Valley Wash North from Moapa, then a rougher 6 or 7 miles East to the range. After gassing up in Moapa, I headed North late Wednesday afternoon. But at mile 12, I ran into a locked gate; Union Pacific had barred the road/right-of-way.

Tangent: When I returned home I googled and emailed Brian Beffort, who was kind enough to promptly reply. The road was un-gated when he last visited in early 2005; the gate is an apparently recent addition.

What followed next was an almost 2 hour dick-dance of looking for hidden keys (I always hide an extra key, why wouldn't they?), searching and trying for alternate roads or drive-able tracks to bypass the Union Pacific gates. At long last I decided to take my chances from the East side of the range, a long drive that involved returning to Moapa, continuing North another exit on I-15 and then heading North on a slow, rough road. Compounding matters, a huge windstorm kicked up. At dusk, about 10 miles North of I-15 I pulled over, cooked and camped huddled in the back of the 4Runner, which served as an excellent windbreak/cave for the night. The wind howled most of the night.

In the morning I continued North on the rough road, then turned West up South Toquop Wash via a very rough 4WD track which I followed for 6 miles before parking. I hiked for 2 hours up very loose, difficult slopes up to the spine of the range, where I could see a ridge leading to the base of the summit about 1.5 miles away. The East side of the summit looked encircled by cliffs, with no visible route up, and it was uncertain whether I could even reach the Ponderosa stand (which was hidden from my view, picture left.) Tired, beat up and bummed out, I turned back.

Monday-Morning QB: In retrospect, I should have parked/camped near the Meadow Valley Wash gate and mtn biked the rest of the driving route the following morning. It would have been a bit tedious, but probably very achievable.

Dreading the road back to I-15, I elected to follow the back roads North into the Tule Desert and then West across Beaver Dam Wash and to the pavement West of the Beaver Dam Mountains. This was longer than I bargained for: 2.5 hours of dusty dirt driving. But the roads were decent, and the big win was… endless, endless Joshua tree forest, the longest, largest, unbroken expanse I’ve passed through. And here, for your viewing pleasure, is a video of 19 seconds of that 2.5 hour drive.

I’ve left the coolest thing about Joshua trees for last. They’re pollinated by only 1 thing, and that one thing is monolectic- specifically the moth, Pronuba Tegeticula synthetica, (yes, our 3rd and final monolectic pollinator from Monocot Week) and even more specifically by the females who lay their eggs in the yucca brevifolia flowers. Both are utterly dependent on each other; there’s no other pollinator for the tree, and no other nursery for the moth.

Joshua tree pollen is unusual in that it’s sticky, not dry, and it seems to have co-evolved with P. Tegeticula to the extent that nothing else can effectively collect and disperse it. But the story gets even weirder: when a female P. Tegeticula enters a Joshua flower (always during night- the only time the flowers open) bearing the pollen of another flower, it deposits it’s eggs at the base of the pistil, but then makes an apparently deliberate side trip to the stigma at the top of the pistil and manually presses pollen into the stigma. This is the only known instance in the world of a pollinator apparently deliberately- vs. incidentally- pollinating a flower. Evolution produces amazing results. I’m glad to have lived while Y. brevifolia and P. Tegeticula are still in the world. They’re unique and wonderful- a standout showcase of the Beauty of the World.

It was a long drive home, but a great week. I could spend endless days exploring in the desert, and if I’d planned my life differently, perhaps I’d be doing so. But for now it’s time to get back home, to my family, my job, my life and the greening Wasatch foothills.