True Grit: Plants That Coat Themselves in Sand

Sand verbena showing pretty flowers and sand-coated leaves. Photo: slandnature.ca

No one likes getting a mouthful of sand. That’s one of the reasons we rinse celery before we eat it. And apparently, other animals don’t like gritty plants either. That may be one of the reasons that certain plants cover themselves in sand.

Called psammaphorous (sand-loving) plants, these curious plants live on beaches and in sand deserts worldwide. There are over 200 species in some 88 genera, so they’re not exactly rare, yet if you saw one, you might not notice it, as sand sometimes camouflages them quite nicely. They all share the same characteristic: sticky leaves that catch and hold blowing sand. 

There are several theories as to why these plants coat themselves in sand. Maybe it’s because, as suggested above, that makes them less palatable to predators. Maybe the sand coating is camouflage and helps hide them from these same predators. Possibly the sand reflects some of the excessively strong light away from the leaves, keeping them cooler (if you’ve ever tried walking barefoot on a beach on a sunny day, you can appreciate that one!) or protecting them from dangerous ultra-violet rays. Or again, the coating might help protect them from damage during sandstorms. Or help the plant absorb more water from dew.

Taste Test

In a 2016 study, Eric LoPresti and Richard Karban of the University of California tested two local psammaphorous plants, sand verbena (Abronia latifolia) and the honeyscented pincushion plant (Navarretia mellita), to see whether the first two of these hypotheses applied: whether sand was a deterrent to herbivory due to animals disliking gritty foods or whether sand acted as camouflage. 

To do so, they either wiped plants free of sand (sand verbena) or coated them in more sand (honeyscented pincushion plant, which proved impossible to wipe clean) to see how animals reacted to them and, sure enough, the less sand they bore, the more likely they were to be eaten. Sand-free plants were consumed twice as often as sand-covered ones in the case of sand verbena. And extra sandy honeyscented pincushion plants suffered almost no damage: only one plant out of 19 was munched on compared with 8 out of 18 untreated plants. 

To test whether this was due to camouflage, they then coated cleaned sand verbena plants in green-colored sand, about the color of the original leaves, to make them stand out from the surrounding tan sand. And—bad news if you were voting for camouflage!—the green sand-coated plants were no more nibbled than those coated in regular sand.

So, for sand verbena, at least, psammaphoryis not linked to camouflage, but rather to aversion to eating sand … which is not to say that other psammaphorous plants don’t use sand as camouflage.

And this aversion to chewing on sandy leaves makes sense: it’s known that the teeth of herbivorous animals feeding in sandy areas wear down faster than those of the same species feeding in other habitats, thus shortening their lives. And, let’s be honest here: eating sand-covered plants is just plain yucky … and I’m a herbivore, so I should know!

Growing Your Own Psammaphorous Plants

Not surprisingly, psammaphorous plants aren’t commonly grown as ornamental plants. Apparently, gardeners fail to see much beauty in plants covered in tiny tan-colored rock particles. Perhaps, though, this article could launch a new trend, replacing the boring tan-colored sand usually covering psammaphorous plants with sand in exotic rainbow colors or even brightly coloured glitter sparkles? 

If you do come up with fun and intriguing ways to grow psammaphorous plants, I’d be pleased to publish the photos in this blog!