A little while back, I published a paper that Rick and I had been working on for awhile. In short, there are quite a number of plants which entrap substrate – sand, dirt, etc. – on their surfaces with sticky trichomes. These species occur worldwide in dunes, beaches and deserts. Quite a number of people, dating back to the late 1800’s, had hypothesized that this “sand armor” must protect the plant, but nobody had actually gone out and tested it. So we tested both the hypothesis that it is physically defensive (who wants to chew on sand?) and that it is a form of camouflage (since of course, it makes the plant look like the background).
|Abronia pogonantha, one of the sandiest plants I’ve seen. Photo: EL.|
We found support for the physical defense hypothesis (in two tests) and did not find any evidence that the camouflage protects the plant. You can read (Inkfish – one of the best science blogs) or hear (Quirks and Quarks) more about this project.
The best part of publishing this was hearing from a prominent researcher (who had noticed this phenomenon), that he tells his students: “if you don’t believe that sand is defensive for the plant – try sandpaper instead of toilet paper!” Since publishing this, I’ve been able to continue this research and observe quite a few more cool sandy plants – some of which were new to me and some of which I had only heard of.
|The best sandy plant in the world. The common names for Pholisma arenarium include “scaly-stemmed sand plant”, which is my personal favorite plant name ever. About an inch tall. Near Morro Bay, CA. Photo: EL|
In that paper, there is a list of sand-entrapping plants. Many of these I had seen and noticed. Others were from published literature. I surveyed a bunch of really good naturalists and they suggested many others (their list was the longest). That is how I happened upon Pholisma, pictured above. This odd plant is a borage (the family includes some wellish-known plants including borage, heliotrope, fiddleneck, baby blue eyes, phacelia, etc.). Looking like a lump – maybe a mushroom? – it is completely chlorophyll-free, instead sucking nutrients from nearby plants (it is an obligate parasite, like Indian pipe, Monotropa, in the east). And the coolest part, of course, is how much sand it catches – it is nearly completely covered! It is very possible that plants which coat themselves in sand suffer a photosynthetic cost because less light reaches them. For Pholisma, that doesn’t matter at all!
|LOOK AT ALL THAT SAND! (I am pretty sure those purple things are flower buds – I didn’t unfortunately get to see a flowering individual).|
Pholisma was, since I learned about it last year, the top of my list of must-see plants and seeing it was one of my spring highlights so far. I happened upon it accidentally while looking at another sand-entrapping plant, Abronia umbellata (I used Abronia latifolia in my experiments).
|Abronia umbellata is not as sandy as some congeners, but it is pinker than most! (there is also a really, really, cool paper on floral evolution in this species – check it out). Photo: EL.|
The central coast of California has three species of Abronia which grow in close proximity on coastal dunes. Abronia maritima is generally on the beach while latifolia and umbellata are a little farther up (and occasionally grow over each other). They each catch sand to some extent.
|Abronia maritima. The yellow anthers are positioned right above the stigma and seem to drop pollen onto it (from my couple flower dissections). It has far smaller flowers than the other species. I’d bet quite a bit that it is selfing. Photo: EL.|
|Abronia latifolia, the common sand verbena for most of the California coast. Common doesn’t mean boring though, its quite awesome. Photo: EL|
Abronia are awesome (everyone knows that already) but there are some smaller, more inconspicuous plants that are also really good at sand-catching.
|Tiquilia has nice flowers, but you have to look really hard to find them (they are tiny). This was a tall individual growing in a less-sandy spot (hence the lack of sand on the leaves and stems in the photo – the bottom still had lots). Photo: EL.|
Another new favorite plant was Centrostegia thurberi. A tiny, cherry red, spiny bizarre thing, it is mildly sticky and has bracts encircling its stems which catch lots of sand – seemingly with stickiness and also just being shaped like a bowl. This was another favorite.
|Centrostegia thurberi. Photo: EL.|
|It catches a lot of sand on its stems, but… (photo: EL)|
|It also does this! Dipsacus – teasel – often has these sorts of bracts that fill with water and mosquito larvae and stuff. I’ve never seen bracts full of sand before (and every plant had them!). Photo: EL.|
And lest I turn completely into a botanist, there were some insects, too. Importantly, there was one caterpillar – Hyles lineata – that was really common in a bunch of spots on Abronia. This species, the white-lined sphinx moth, is common over much of North America some years and absent others. Fortunately for me and unfortunately for many herbaceous plants, it is having a good year in southern California (especially near Anza Borrego).
|This Abronia villosa is not as happy as I am about this big (3″+) final-instar caterpillar. Photo: EL.|
While Hyles likes to eat Abronia (I’ve found them on pogonantha, latifolia, umbellata and villosa this year), they not like to eat sand at all. While it doesn’t have a good mechanism for taking it off, it seems to concentrate on nonsandy plants first and then on nonsandy parts of the plant, but it always ends up eating the sandy parts of the plant eventually.
|A green-morph H. lineata on pogonantha. They come in lots of colors – black, green, yellow and all manner of in-betweens. They all seem to turn into identical moths. Photo: EL|
Unsurprisingly as they don’t like it, sand on plants is damaging to them. A normal Hyles mandible at pupation looks like this:
|An SEM micrograph of the right mandible of a Hyles lineata fed on nonsandy Abronia latifolia. Those “teeth” are for grinding up the plant before it enters the body. Photo: EL|
But if they eat sandy plants, they get pretty rough:
|Look at the “teeth” – or lack thereof – on this right mandible, from a caterpillar feeding on sandy A. latifolia. Photo: EL|
That’s it for today: a description of a study, some weird sandy plants, and a teaser of a future paper…