A Neotropical Savanna

Seeing it with Michael – One of the first plants our friend and naturalist, Michael, pointed out to me during a tour of our newly purchased property was a young, shin-high shrub. He reached down and rubbed a leaf and said, “This one is a sandpaper plant,” or words to that effect. He had me feel the leaf, and sure enough, it was coarse as sandpaper.

We had already decided to keep as many trees as possible on the property, and to encourage other interesting plants, but when we saw that the leaves of the sandpaper plant also frequently took on a nice reddish color, we doubled our efforts to see that these plants did not get cut down, either by us or by our gardener.

Seeing it flower - But it wasn’t until this year that I had enough time to watch for signs of flowering. On January 12, I first noticed a plant with buds.

And a week later, January 19, I saw my first flower:

It seemed a little strange that there should be only one petal (the yellow tongue hanging down in the picture), so I decided to keep watching. Every now and then I’d see another flower or so but invariably I didn’t have my camera with me. Finally, on January 23, the flowers on one plant were suddenly open and covered with bugs! (Click on either image to enlarge. You’ll love the bugs.)

I’m assuming the bugs are the pollinators. They were certainly busy! After uploading the images to the computer, I wasn’t satisfied with them and decided to take some more, even though the wind had picked up and was gusting. One hour and twenty minutes after taking the last of the above pictures, I found this sight:

The petals were gone – all of them! All that’s left are the sepals and the stamens, along with a few pollinators. I mean, those bugs were busy, but did they knock off all the petals? Or was it the gusting wind, which seems not to have disturbed the flower petals of other plants in the vicinity? Regardless of the cause of the disappearing petals, it’s small wonder I haven’t been able to find good pictures of the flowers on the internet!

The Sandpaper Plant is in the Family Dilleniaceae – Whenever I look up sandpaper tree or sandpaper plant in the index of a plant book, I am directed to a description of a plant in the Family Dilleniaceae. The Family name comes from an old-world tropical tree that Linneaus himself named – Dillenia in honor of his friend, the German botanist and physician Johann Jacob Dillen. There’s a nice illustration of a Dillenia flower in wikipedia.Members of the Dilleniaceae family have papery fibrous reddish bark (Gentry)

Their leaves are often rough and sandpapery (more on this later) with straight, parallel, close-together secondary veins (easier to see on the underside, shown below and more easily seen in the enlarged image – click on it), connected by subperpendicular, strongly parallel tertiary veinlets (Gentry)

Note that the secondary veins are not really straight in this species, but they are definitely parallel, as are the tertiary veinlets.The petiole (leaf stalk) is often narrowly winged and usually more or less continuous with the wedge-shaped leaf base. (Gentry)

The winged petiole is pretty clear here, but the wedge-shaped leaf base (where the leaf and petiole meet) is better seen in the previous illustration.The flowers have many stamens (the pollen-bearing male parts inside the petals). The bugs are all over those stamens.

Is it a tree, a shrub, or a vine? All the books I mentioned earlier that have sandpaper plant in the index take me to a description of a tree, Curatella americana. I’ve been watching the sandpaper plants on our property for three years now and only one of them looks like it will grow into tree. That one isn’t pictured here – it’s not in bloom right now, and it’s also pretty scraggly. Further, the flowers of the tree Curatella americana are described as cream-colored in Costa Rica (Zuchowski) and as light green in Panama (Carrasquilla). The plants here look like shrubs, but there’s one plant in a more shaded area that suggests it could be a vine. The next three images follow the main stem as it reaches up toward a tree branch.

Gentry does say that the family Dilleniaceae is mostly lianas, or vines. The answer to whether this plant is a tree, shrub, or vine came from Robin Foster of the Field Museum of Chicago, who has been of great help to this bumbling amateur. He explained that the photos I sent him were of the genus Davilla, which is “…usually a liana [vine] but when growing in an open area can be shrubby.” He also mentioned that the plant “…will develop yellow fruits formed from those two cup-like calyx lobes, until they finally open when ripe.” He calls the Dilleniaceae the sandpaper family. And how do I tell this liana/shrub Davilla from the tree Curatella found in my reference books? Foster says that Curatella will have a “larger longer leaf with a very wavy margin.” So I’ll keep my eyes open.

What about the sandpaper? Foster calls this the sandpaper family, Carrasquilla [Trees & Shrubs of Panama] says the leaves of Curatella are used as sandpaper, and Zuchowski [Tropical Plants of Costa Rica] says that silica in the leaves of Curatella give it a sandpaper quality. So, do the leaves of Davilla have silica in them as well, and can they be used as sandpaper? The leaf certainly feels rough, so I decided to scan it so I could magnify it and look for silica spikes. Here’s what I found:

The arrows point to just a few of the silica spikes. The leaf is studded with them. Then I tried using a leaf as sandpaper. It can be done. My “before (left) and after (right)” shots were taken pretty casually and so don’t show the difference very well, but it was there, trust me. Clicking on either image will give a slightly larger view, which might help.

However, before you decide you can go into the sandpapering business just by growing a few Davilla plants, be forewarned that I used up the silica from an entire leaf on this section of a small stick. Just be sure you have lots of plants in your area before you take on a sizable sandpapering project!

UPDATE: Thanks to Gordo’s comment (#3 below), I decided to provide a link to the Field Museum’s Tropical Plant guides, which show a few different Davilla species. Find those images at http://tinyurl.com/yry334

Also, here’s an earlier picture of the leaves – better exposure than some of the images that went with the story.