Yucca baccata and Opuntia santa-rita looking like futuristic stainless steel sculptures.

Friday, December 7, 2018 is a very rare night out here in the desert where I live: It’s dewy. This is because it just rained and it is winter and the temperature is 35 F (2 C) and the humidity is 100%, which it almost never is here. What this means is that a microscopically fine layer of truly tiny dewdrops has formed on everything. And when this happens on succulents and other plants with waxy blue leaves and stems, they refract light just like reflectors. Agaves and yuccas in particular are shining like traffic cones, visible from a hundred or more feet away using just a small headlamp. Some of the glaucous prickly pears look like they are made of aluminum tonight, like this normally purple Santa Rita prickly pear cactus growing next to a clump of banana yuccas, also shimmering like quicksilver in the night. It’s really rather amazing – while I have seen this effect before in years past, this might actually be the single best time I’ve yet witnessed. It’s utterly surreal and magical.

The same scene as above, taken by daylight the following day, for comparison. The dew evaporated with the sunrise and the plants are dry, as they typically are around here. Note how purple the Santa Rita prickly pear is and how the yucca leaves are ordinarily green with a slight gray tint.

Opuntia chlorotica cloaked in a thin sheen of shimmering silver dew.

The extraordinary layers of dew that have formed on everything outside tonight are by far the most visible on plants with waxy, bluish- or white-surfaced leaves. This reflective effect is not happening on green foliage, although I suspect that if the dewdrops were to freeze (which it probably won’t quite get to) then we’d see some effect upon green leaves as well. Here, a pancake prickly pear (Opuntia chlorotica) shines in front of a California juniper tree (Juniperus californica), whose waxy blue berries sparkle like a galaxy in the background.

The same Opuntia chlorotica the next afternoon, Sat Dec 8, 2018. The juniper berries, while pretty enough, don’t particularly draw the eye in this photo, simply because they are not reflecting so much extra light. (Plus of course it is daytime….)

The surreal effects of light and dark, in a fashion seldom seen in my desert garden.

These photos look almost like they are taken in black and white or perhaps with some sort of special filter, but they aren’t. This planting of agaves and yuccas is beautiful under any normal time of day or night, but when covered in microscopic dewdrops, it’s celestial.

And by day….

Agave ovatifolia and Yucca rigida as if they were being lit from within.

The two prominent plants in this photo are Agave ovatifolia (whale tongue agave) up front, and Yucca rigida (Mexican blue yucca) in the back, both gleaming in dew that reflects light amazingly well. But careful observers will also see the distant agaves in the background, and even the pinpoints of light reflected off of juniper berries. There is no way that those distant plants would be visible at night with a flash 30 or 40 feet away on a normal night without tiny water droplets to arc the light of a flash back to your eyes. This illustrates the unique conditions out here this lovely, if chilly, desert winter night.

The next day. As stated earlier, there is no way you’d bother to pay attention to the juniper berries in this photo, but they are notable at night under specific conditions.

The dewy highlighting plays out across numerous unrelated plant species.

Any bluish, wax-coated leaf surface is exhibiting the reflectivity tonight. Here is a lesser bottlebrush shrub (Callistemon phoeniceus hybrid) from Australia glowing in the darkness, while green-skinned cacti like the tall Argentine toothpick cactus (Stetsonia coryne) and Nolinas are their ordinary color, despite being covered in dew as well. It appears that the pale blue to white wax layer behind the microscopic water droplets is key to creating this effect.

The Callistemon phoeniceus’ normal daily coloration is bluish-green. The only thing that is different about the foliage is that it is dry here the next afternoon. The golden barrel and other plants look essentially identical both during the day and at night.

Eucalyptus websteriana glows ghostly white at night.

Waxy-leaved Eucalyptus are also showing the dew-reflector look tonight, in keeping with the theme of the 5 or 6 photo pairs above. So beautiful, so ethereal. Here, Eucalyptus websteriana looks much whiter than usual, while equally wet Euphorbia antisyphilitica and golden barrel cactus look more or less normal in color.

I find these comparative photos taken only 16 hours apart amazingly instructive, and hopefully readers can get a sense of how unearthly the difference between normal nights and exceedingly rare dewy ones is.

Aloe melanacantha (black-spined aloe) blooms in early winter. It’s about the only plant that flowers at this time of year, aside from Ferocactus latispinus, which also does.

The same scene the day before the dewy night. The aloe flowers are quite a strong reddish-orange, although you would think they are a softer reddish-pink based upon the nighttime photo.

Aloe melanacantha and companion plants in my front walkway garden by the house. I see these plants multiple times daily, which of course is why I planted select species here.

I’m going to reverse the order of this final comparative pair of photos and put the daytime picture first, because it was actually taken first, unlike the other photos up until this point. I took this photo at about 12:35 PM and then posted it on Facebook on Friday Dec 7, 2018 shortly thereafter. This was less than a half hour after the final rain showers of the frontal band bringing the wet weather  had cleared off to the east, allowing the sun to start breaking through blue patches in the sky. (D:F Ranch received about .3 inches of rain, or 8 mm.) I just liked the scene and colors and the fact that the aloe was coming into prime bloom with its first basal buds about to open. But I didn’t know at the time that that evening would prove to create the perfect conditions for the dew layer featured so prominently in this post.

Night shot of the same scene taken less than 12 hours later.

The exact same scene taken from the same position at about midnight, less than 12 hours after the daytime photo. Note how the dew layer has dulled the aloe’s flower color while whitening the leaves of the Agave flexispina to the right and the Aloe glauca in between them. The green foliage of the Aloe melanacantha has not been affected by the dew in terms of color or reflectivity. The tall tree aloe “Hercules” in the background has also acquired some reflectivity that it normally wouldn’t have.

Close-up of the flowers of the Aloe melanacantha. The larger water droplets are probably raindrops left over from that afternoon, while the minuscule dewdrops have all formed since darkness fell. Note how the larger raindrops don’t reflect white light nearly as effectively as the microscopic dewdrops do.

A close up of the leaves of the Eucalyptus websteriana, also illustrating how the dinky dewdrops are what causes the velvety white appearance. Touching the leaves and forcing the dewdrops to run together destroys this effect, just as writing your name in condensation on a window pane does the same thing.

Macro shot of the Agave flexispina leaves, showing the same ultra-thin layer of dew that makes the leaves look silver under reflected light.

The appropriately-named Australian emu bush (Eremophila) “Fire and Ice” illuminates the foreground with a bookleaf mallee (Eucalyptus kruseana) in the back. All mercury-silver until dawn.

Walking down the driveway and through the garden with these ghostly glowing plants in the inky darkness was dreamlike. They were so strangely visible when compared to my normal nights of working outside!

Parry agave (Agave parryi) and Yucca baccata looking a bit like neon signs in Las Vegas. The saguaro cactus and teddybear cholla in the background both utterly lack this glowing effect. Why?

A waxy cuticle on the leaves of Agave parryi enables the microscopic development of light-reflecting dewdrops under certain narrow atmospheric conditions.

The answer clearly is the wax layer found on the epidermises of the plants that have this glowing effect. Many xeric plant species in numerous families secrete various types of wax that helps retard water loss. Under scanning electron microscopes, these wax crystals look like overlapping shingles in some species, and tangled threads of twine in other species.

Juniper berries have waxy cuticles too. Many plants do, as we will be seeing below….

As a general category, most surface waxes secreted by various plant species are called epicuticular wax, meaning “on the skin”. These waxes are made up of a number of different compounds mostly included under the umbrella term of “straight-chain aliphatic hydrocarbons”. The composition of these waxes vary but tend to be relatively simple as far as chemical compounds go.

Potted plants also showed this effect to varying degrees, including these juvenile Joshua tree and banana yucca seedlings, as well as other aloes and agaves in the background.

Delving briefly into chemistry, an aliphatic compound is a simple hydrocarbon that lacks a stable carbon ring in its molecular structure, hence the name “straight chain hydrocarbon”. The smallest aliphatic hydrocarbon is methane, which is just one carbon atom bonded to four hydrogen atoms. A slightly more complex one is ethane, which is two carbon atoms with 6 hydrogen atoms, and then propane which has 3 carbon atoms and 8 hydrogen, butane with four carbon and 10 hydrogen, and so forth. Waxes have longer carbon chains and are more complicated than simple hydrocarbons, and might contain different elements like oxygen or nitrogen, or double bonds between carbon atoms that changes the amount of hydrogen that they contain.

Myrtillocactus geometrizans shows the distinct reflectivity at the apex of each stem. Epicuticular wax tends to be most abundant on newer tissues and tends to degrade or wear off on older ones, which is why the more basal portions of the cactus’ stem are simply green and don’t reflect the light.

Epicuticular waxes have different names indicating which chemical class they fall into. Examples include words such as paraffins, secondary alcohols, di-ketones, and tri-terpenes. These waxes may be quite familiar to us even if we don’t know their specific names: We have all seen and eaten the white bloom on plums and grapes, marveled at the way water beads up on kale, cabbage, and water lily leaves, and observed the bluish-white tint in the foliage of blue spruces, junipers, certain palms, and yes, succulents. Waxes are widespread and abundant chemicals in the botanical kingdom.

Hoodia gordonii clearly has a substantial wax layer, as it, too, is exhibiting this effect.

Epicuticular waxes have effects upon plant biochemistry other than inhibiting water loss. They can also regulate the absorption of potentially harmful chemical compounds into the plant’s body; reflect ultraviolet light or intense visible light in deserts or tropical regions, which reduces leaf or stem overheating; act as a self-cleaning mechanism by repelling pore-clogging dirt and dust; and making a slippery surface too difficult for insects seeking food to climb. This wide array of purposes is why these waxes are manufactured by thousands of different plant species.

Aloe “Hercules” has developed the reflectivity, while the nearby Oreocereus hendriksianus has not. Both plants have a waxy water-retarding epidermal layer, but only one is showing the light refractive effect under identical conditions of weather. By the way the juniper tree in the background is a male and will never produce berries, so that’s why it doesn’t stand out the way the female trees do on a night like this.

Most cacti and agaves have a definite wax layer on their stems and leaves, but not all of them are blue or white. Many fairly waxy plants are actually quite green. These color differences in the waxes secreted by the plants are probably the result of chemical variances and separation into the aforementioned classes. The observed fact in this post is that the dewdrops reflect light by far the most strongly in whatever waxy compounds appear pallid, glaucous, whitish, bluish, or whatever other shade of pale to our eyes. Green waxy plants like saguaros, barrels, green agaves, and so forth do not have any extra reflectivity despite being just as wet as the ones that show it. Interesting, isn’t it?

While boojum tree leaves (Fouquieria columnaris) don’t look especially pale, clearly whatever epicuticular wax they secrete is amenable to the dew effect tonight.

Speculating for a moment about what causes some waxes to enable this light reflection, I ask a series of questions. They include, “Is this a function of one particular wax, one entire class of waxes (such as paraffins), or something else entirely? Does a wax absolutely need to appear pale blue or white to our eyes in order to work this way? Is the wax acting upon the water in the dew causing micro-beading? Is the cumulative effect of millions of individual droplets all acting as tiny prisms what makes the white light of my camera flash or headlamp shine back at me so strongly? Do other waxes cause more of a ‘sheet’ of moisture as opposed to individual droplet prisms, thereby preventing the reflective effect?”

So many questions that I am not qualified to answer with any certainty. I wonder if anyone else has already studied this? 🙂

Native desert perennials like the small odora bush (Porophyllum gracile) on the right also have a powerful reflective look on this night, as does the Agave macroacantha to the left. The narrow stems of the odora are individually almost unnoticeable, but in aggregate they are as bright as the agave, albeit significantly more bluish. The claret cup hedgehog cactus (Echinocereus triglochidiatus) in between them has no enhanced reflectivity.

Bulbs are getting in on the act too. This Boophone haemanthoides shows a brilliant luminous effect, while the golden barrel as we’ve already seen above does not. Narcissus foliage (not shown) is also glowing with dew.

Knife-leaf acacia (Acacia cultriformis) is also in the parade. The party truly welcomes a huge variety of different plant genera. It amazes me!

This is the last shot of the night. I don’t expect to see this effect again this year, although it could potentially happen again before spring arrives in 2019.

I chose to end with the photo above because it shows a good range of plants that do and don’t exhibit the dewy reflectivity. The well-lit plants include the Agave “Cameron Blue”, the banana yuccas, the juniper berries, and to some extent the Eucalyptus sargentii tree. Non-lit plants include the Penstemon eatonii, cholla, Ferocactus rectispinus, Trichocereus “Pink Glory”, or the trunk of the Baja cardon (Pachycereus pringlei) in the back. The linear-leaf yucca (Yucca linearifolia) to the middle left shows both traits, with the fresh young central leaves having a strong propensity towards gathering enough dew to glow, while older leaves on the outside do not.

Whatever mechanism conspires to create this effect, it is rather rare in my neck of the desert, and I cherished the opportunity to observe and photograph it and then write about it. I have so many widely disparate blue or glaucous plant types that all showed the glow, while other green ones in the same genus growing mere feet away did not. This led to my interesting research into the role that epicuticular waxes play in this phenomenon. And since I love writing, learning, and photography, it’s been a good ride. I hope readers enjoyed the journey too!