Thursday, August 30, 2012

Jewelweed - species profile

What: With my last post on poison ivy, I wanted to return to another good friend of mine: jewelweed (Impatiens capensis). In Centennial Woods, we only have spotted jewelweed (the yellow-flowered pale touch-me-not is found on much richer sites). I spent some time observing it while watching the hummingbirds, admiring its simple elegance. The flowers are so rich and ornate, with no shortage of suitors begging nectar. It grows abundantly anywhere there's water so I headed down into Centennial Woods below the sandy slopes and found a great patch to take some photos.

Ecological notes: Much like raspberry stems and boxelder twigs, the stalks of jewelweed have a weird white powdery bloom to them. I still have no idea what the function of these is, so if anyone knows, send me an email! I was told that it was yeast, but some sources say that this is just a myth wine makers false propagated. I would assume it might then have something to do with resistance to predation by insects or maybe it's a fungicide or for preventing water loss? Researchers in Osaka found that the bloom, at least on grapes, is oleanolic acid. They link it to preventing dehydration. Since jewelweed grows in intermittently wet areas, the bloom could prevent the plant from losing water in droughts (like right now) and thus maintain the stem's rigidity. Sounds reasonable. But why would boxelder twigs have the bloom?

Minute hairs on the surface of the leaves trap air and cause water to bead on the surface. When you hold a jewelweed leaf underwater it seems to transform miraculously into silver! These leaves were holding some of that much needed rain from last night. Many other plants do this too, and since it's a pattern we have to have a super cool esoteric word for it: superhydrophobicity (really afraid of water!! aka the lotus effect). Some plants achieve superhydrophobicity by having a dense coating of bristly hairs, others, like lotus, have waxy cuticles. Supposedly this is linked with both water retention as well as being able to wash leaves clean, even with dew. Since the water beads up it has a high internal charge and will pull dust and other stuff off the leaf surface. 

Yesterday I was noting that many had the malformed flowers, or galls. Inside that green blob there's a Jewelweed gall midge (Schizomyia impatientis). They hatch early fall and overwinter as adults. 

Where: There's a great patch of the spotted kind in CW where an intermittent stream drains off the slope (it's been dry most of the summer though) and you can follow the flow of the water by where the jewelweed grows. Jewelweed definitely prefers wetter areas. So when you find poison ivy, often times walking downslope or finding a drainage will yield a good patch of jewelweed.

Other notes: Jewelweed is pretty easy to cultivate. It's herbaceous, so it dies back every year, but it has perennial roots so it shoots up from the same spot each year. The seeds are spring loaded so when you touch them they erupt out from the pod (see the image of a swollen pod above). They're just now ripening. Seeds taste like walnuts and they've got about 3-5 per pod. Because they shoot so far they'll easily colonize a nice little patch. Ask Zac to see his jewelweed garden started from a single plant!


  1. Love this post, but one qualm: Jewelweed is an anual, right? It seems like a perennial in the way it claims a spot and reliably comes back year after year but I suspect that's due (at least in my backyard) to the massive seed bank it creates in the soil and its ability to thrive in low light conditions. My patch is still throwing out high numbers of seeds even as the vegetative part of the plant is turning yellow and brown and starting to die back.

    1. An oversight on my part. I had assumed perennial roots, but some research suggest that members of the Impatiens genus are perennial only in milder climates. I think your reasons are spot on though, of why it appears to be perennial.