Botany Photo of the Day

Before I get into the details of this New Zealand native, a word about australis / australe since the word appeared yesterday as well. Contrary to what I've read on some nursery sites, this is not Latin for “of Australia”, but rather for “south”, as in the southern hemisphere. Aurora borealis - northern lights, Aurora australis - southern lights: that's how I remember it.

To put this plant in context, you first need a few more facts than what this image can provide. Start by checking out this perspective image of Raoulia australis, which will give you an idea of just how small this vascular plant really is when you compare it to the nearby gravel. Second, you need to know that this plant is in the family Asteraceae. Third, you also need to know that the Asteraceae also includes sunflowers, which are perhaps two thousand times as high as this little mat-forming plant. For comparison's sake, that's roughly the difference between my height and the tallest building in the world doubled.

If you're like me, you can only marvel, simply marvel, at the amazing diversity of forms and structures that have evolved.

So what are the ecological advantages of being low and small? In this case, I suspect it has to do with prevention of water loss. Raoulia australis, or scabweed, grows in dry, rocky areas of the South Island of New Zealand, ranging from high coastal elevations to alpine. Mat growth forms are ideal for water conservation: a low surface area prevents wind dessication; water requirements for nutrient transportation are low due to compact growth; and, in this case, water is “stored” in the peaty decaying layer of older leaves below the fresh growth instead of draining away into the rock or sand. In the perspective image, you can see a black fringe surrounding the mat, particularly the bottom left - these are exposed decaying leaves. It seems to me that this might be an indication that the plant is not doing well, and is contracting instead of expanding.

I only took this photograph at the prompting of Joe Keller from the Alpine Garden Club of BC, who said it would make a great “Stumper” for UBC's online forums. The calibre of the people on the forums is just too good though, and it was answered by the second person to reply. Stumpers is a new forum where the most active forum members can challenge everyone's plant knowledge by asking a plant-related question with only a few clues. Yes, we're plant geeks, but it's fun, and everyone can learn something.

If you've read this far, you deserve a reward. Here's a near full-size image of Raoulia australis for you to use (subject to the Creative Commons License, of course).

Update (June 10, 2005 9:45 AM PST): Two small bits of book-keeping. First of all, I was displeased to note that a trackback ping from an unsavoury site was received only a few hours after posting this, so I've taken off trackbacks for the time being. Second, thanks to Neil for pointing out to me that relative links don't work in Bloglines (and I assume some of the other feed services), so I've made the necessary changes.