In contrast to the well-known and vibrant displays of springtime wildflowers, deserts are generally not thought to have much in the way of autumnal leaf coloration. This is not universally true, however.
Little-known fact: Ocotillos (Fouquieria splendens) can turn some very lovely colors in fall as they prepare to go dormant for the winter. Wet summers followed by a long and slow autumn drying period as days cool tend to result in the best foliar show. If drying is too fast or too early after a dry summer, the leaves simply drop quickly without turning anything other than tan. But if they linger due to soil moisture, and nights are cool and days are warm, the colors are really brought out.
Most ocotillos are yellow when they turn, but orange and russet are also present. Genetics appear to determine how orange or red they become. Beautiful, aren’t they?
It may not be Vermont, but it’s beautiful in its own right.
This is fall color in northwestern Arizona. Several species of yellow-flowering shrubs plus the deciduous leaves of ocotillos, which can turn shades of yellow, orange, or russet as days shorten and colder weather approaches. The fall-blooming shrubs in the photo above are mainly composites such as broom snakeweed (Gutierrezia sarothrae), showy goldeneye (Viguieria deltoidea), and paperflower (Psilostrophe cooperi).
The ocotillos are going dormant for winter now that it is approaching November. It’s the same as aspens or maples turning colors and losing their leaves as weather turns colder and days get shorter – the green chlorophyll breaks down and the other pigments normally hidden by the green are exposed, just before the leaves drop off. It’s normal and this is what we get for fall leaf colors. It’s also been dry for about 5 weeks now so the surface layers of soil are turning rather dusty again (this is the desert) and that helps encourage the ocotillos to go dormant. They’ll green up again next spring.
Thinking back to spring, I remember that these same hills were golden from the brittlebush shrubs (Encelia farinosa) six months ago, and now we’ve gotten a second showing for autumn, albeit with different species. We saw this rare double-blooming cycle as a result of well-spaced rains in winter for the spring show, and summer for the fall show. This bimodal rainfall pattern is a huge factor in contributing to the overall lushness and diversity of the Arizona deserts – it’s not nearly as harsh to survive only a few months without rain as opposed to nearly a whole year, like some deserts have to do!
Ocotillos resplendent in fall glamor less than a mile from my house.
October 21, 2013 was a serene fall evening in the colorful ocotillo forest about 3/4 mile from my abode. Calm, warm, and windless sunsets make for good photographic conditions. The next strong wind will probably defoliate most of these plants, so the window of fall foliage enjoyment is fairly short. I am glad I caught it.
Most people express surprise at this fall foliar show. And indeed we are better-known for spring flowers (and to some extent late summer ones) but the leaf-peeping season is a well-kept secret. You do need a lot of ocotillos in a given spot to have a significant foliar visual impact, however. Fortunately, my immediate region has large numbers of big ocotillos to pull this off.
School colors. Green and gold are a classic combination of colors for many sports teams. I’m going with Team Ocotillo. Go Okies!
Gold and blue are also a great combo.
Detail of leaves on a russet-reddish ocotillo stem.
Ocotillos, saguaros, and buckhorn chollas all grow together in this scene just across the road from my place.
Joshua trees also grow here with the ocotillos. This mix of Sonoran and Mojave Desert species is a gigantic part of why I fell in love with this area and wanted to buy property here.
Banana yuccas (Yucca baccata) are in the mix too.
Leaf colors are enhanced by the orange rays of the setting sun. It’s just a few minutes at the end of the day (or the beginning) but it’s worth trying to catch on camera!
Some ocotillos rebloom a second time in autumn. Here, a lone sprig of flowers emerges in October in front of a backdrop of goldeneye sunflowers (Viguieria deltoidea).
A small percentage of ocotillos will flower in the fall most years – maybe 1% to 2%. Some put out a single flower at the end of one branch, while others do a smaller repeat performance of the spring show on multiple canes. They don’t seem to set seeds very well in this secondary flowering, however, which may well be a result of their isolation from other blooming plants, preventing cross-pollination. Basically ocotillos are a spring-blooming plant with a fall curiosity show in a handful of exceptions.
Wait, is this April or October?
Note how the ocotillos on the drier slopes behind have started to turn colors and drop their leaves for winter dormancy, even as the foreground plant in the wash channel is fully leafy and setting a second crop of blooms. This looks like it could be lifted from a springtime floral album. However the presence of summer-growing coyote melons and lemonscent daisies help confirm that this is a fall photo, not a spring one. 
We recently saw, and photographed, an ocotillo with yellow flowers. This seems to be quite rare, we will check it next year to see if the yellow blooms continue. I have only seen one other instance of this, it was reported to be in the Big Bend area of Texas. Our discovery is in the eastern desert of Imperial County, ca.
Yes, yellow flowers on ocotillos are exceptionally rare. There are only a handful of documented cases of it, including a few in the Big Bend region of Texas (as you noted), one or two in or near Organ Pipe Cactus National Monument AZ, and a couple up near where I live in Mohave County AZ. I know of none from California, at least not before you wrote to mention this one in Imperial County. I’d be interested to see any pictures of it and if you are able to discover any others. From what I’ve seen myself and heard via discussion with others who know about these types of things, where there is one there sometimes are a couple more. They appear to occur in clusters and are not evenly distributed through the population at large across the plant’s range. My email is Jan at DFRanch dotcom if you care to shoot me a few photos.
Yellow pigmentation is probably a recessive trait in ocotillos (caused most likely by a lack of the orange/red pigments that dominate) and I suspect that seedlings originating from yellow plants that germinate will almost all flower red. It is only when you backcross these seedlings with each other and replant those seeds, that the second generation will probably contain at least some yellow flowering plants. This is due to inbreeding, which is generally not a good thing for any organism. There might also be other floral colors too, perhaps orange, salmon, or pink?
I am speculating about all of this because honestly, no one has ever tried this to see whether it’s possible to induce additional colors in ocotillo flowers because so few known yellow flowering plants exist, and getting two additional generations of flowering-size ocotillos will require a long term commitment spanning a minimum of a decade or two. Clearly the genes exist in the species but the odds of a genetically double-recessive seedling surviving to adulthood in the wild are lottery-odds low. That’s why we see so few of them.
Crested saguaro cacti are thought to be very rare, and some have claimed them to be a one in a million occurrence. This is not entirely true, because we now know that there are at least 2500 or so documented cases of crested saguaro cacti in Arizona alone thanks to the work of Bob Cardell from Tucson who has spent roughly 20 years, maybe more, hiking to and documenting the precise locations of at least that many plants. (Some have died, but he has a history of where they once existed if so.) This also ignores the fact that there are a roughly similar number of saguaros south of the border in Sonora, Mexico and crested plants are known from down there too, albeit in much less detail. A more accurate estimate of crested saguaros is likely closer to one in ten thousand, which is still rare, but it’s decidedly not impossible to find them. But finding yellow flowering ocotillos truly is a one in a million occurrence, so congratulations!