mirabilis_close.jpgMirabilis multiflora (Desert Four O’Clock) is one of my favorite Colorado native plants. Part of what makes it a favorite is that it successfully grows in my landscape. It’s planted along the south foundation of the house in an area that gets no supplemental irrigation. So, yes, it is a drought-loving plant that loves HOT locations. And in the height of the summer, around 5:30 or so (it apparently cannot tell time), it opens beautiful little magenta blooms that last until late the next morning. Some years it reblooms later in the season.

Given the conditions this plant will take, you probably won’t be surprised to learn that it has a tap root. I’ve never been able to pin down just how long and large of a tap root it can grow. I see descriptions like “VERY tap-rooted,” “does not transplant well because of its large taproot,” and “substantial taproot…up to 12 inches in circumference.”Since this plant dies down to its tap root each year, each spring I have to go through a period of faith that there really is this magical tap root down below, storing energy and gearing up to grow a whole new above-ground portion each year. I’ve worried some years when we’ve had especially dry conditions that the root may have shriveled up and died underground. Just how big and substantial is this tap root?! I had dreams of digging one up and then laying it on the ground with the full taproot on display for measuring and photos. (The Mount Goliath Dos Chappell Nature Center has done something similar with the aptly named big-root spring beauty, Claytonia megarhiza, a little four-inch wide alpine rosette with a massive tap root.)

Luckily for me, my friend Christine needed to plant a new tree last year, and there happened to be a few volunteer Mirabilis multiflora growing in the area she was planning to disturb. She offered her specimens up for excavation, and I quickly agreed. These were not terribly old or large plants, so I figured we’d end up with “junior” versions of the taproots. I headed over on excavation day with shovel and camera.

Well………we had NO idea what we were getting into! And I can honestly say, I still have not excavated a complete Mirabilis multiflora root. Here’s how the excavation went:

First, here are the cute little plants, oblivious to their imminent removal:

Our first victim, a two year old plant, maybe eight inches in diameter (in April, so it was early in the season):

We quickly realized, this was one substantial plant under the ground! (At first, I thought we’d come across a tree root from a neighbor’s cottonwood.) Oh, I so wish I could have gotten photos in which the emerging root system was easier to see. You can easily see lateral roots, but the very large central taproot is in the foreground:

Finally, after digging down almost three feet with no end to the root in sight (in fact, it wasn’t even tapering to a smaller root yet), we accidentally snapped the tap root and a very large lateral root. Wow. (It smelled like potato, weird!)

So, still no answer to my question about how big they get. But I now have much more confidence that my plant will overwinter just fine. I also have a mental picture of what’s going on underground. This was a substantial tap root indeed!

My friend Christine also happens to be a supremely talented botanic illustrator, and she documented part of the tap root in this fantastic illustration.