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weed that explodes seeds

Weed that explodes seeds

Jewelweed, Impatiens capensis, is now setting seed pods, and if you have kids you’d like to enjoy wild foraging, this may be the right plant at the right time to get them interested. Because to harvest these edible seeds you have to capture them in your hand as the seed pod explodes. That’s unique! Most wild foods don’t exploding and will stay still so you can pick them or dig them up. Not jewelweed.

The technique is to surround the dangling seed pod with your fist, being careful not to brush against it as you get into position. Once your fist is loosely closed, move just enough to brush up against the pod and it will explode its seeds into your hand. The darker seeds are the ripest, but the small green ones are also edible. Discard the expended curled seed pod. The seeds taste a bit nutty, mild, and interesting. Some describe the flavor as like a walnut. I think they are milder than that. You won’t capture enough for even a serious snack, but they are really fun to enjoy both the capture and the nibble as you walk in the woods.

Another common name for jewelweed is touch-me-not. It is related to the Impatiens in many gardens.

Miller Woods was full of jewelweed last time I was there, but any wet area is likely to have it. Look for the orange flowers, lobed leaves, and it is the only exploding wild edible you will encounter in this area.

Jewelweed is better known as an antidote and treatment for poison ivy. Applied just after exposure it can prevent the skin reaction from the poison ivy’s urushiol. If you do have an outbreak of poison ivy, the juice ftom the stems and leaves will ease the irritation, and in my experience will also make the rash heal more quickly. Jewelweed juice also eases bee stings, wasp stings, mosquito bites, and minor skin irritations.

Just by rubbing the plant between your fingers or against your skin you’ll get a lot of juice. You can put it in the blender with a small amount of water or use a juicer. The juice can’t be saved by freezing – it does mold easily – but can be added to salves or even homemade soap.

The plant is edible, but high in selenium, so only the early spring shoots are eaten and then only with at least one change of water which is then discarded. I did eat some many years ago, and I didn’t find it appealing. I’ve had friends make and drink a mild infusion (leaves and stems steeped 20 minutes in a closed container) as another way to prevent poison ivy. Anecdotal information says this can help.

Jewelweed is a beautiful, helpful, and prevalent plant. And if you don’t want to eat the seeds, carefully pick the seed pods without touching them, and throw it at your closest friend. Just for fun. It is a soft explosion that is likely to make anyone laugh.

Linda Diane Feldt is a local Holistic Health Practitioner, writer and teacher. She has a daily twitter feed on wildcrafting. For more information, her web site has articles and class information.

Photos by Linda Diane Feldt in Mary Beth Doyle Park


Linda Diane Feldt

Fri, Jul 31, 2009 : 9:50 p.m.

Here is one of the on-line sources. On the site, scroll to the fourth box and click on WILD PLANTS, then alphabetically to Jewelweed. A little over half way down the page, information on the seeds. I have another source, but will need more time to find the book again. This was a new one to me as well. I had to try it first, of course, and had a chance to do that with a friend last week. Steve also has a book out, available on his web site. As I mentioned, some do eat the plant with a few changes of water. One source said the problem is high levels of selenium. I had eaten it before, as well as used as mild infusion (steeped 20 minutes) to prevent poison ivy reactions. It recall it was OK but not that tasty, and the information on it preventing poison ivy outbreaks from internal use is anecdotal, but directly confirmed from a number of people who are usually sensitive to poison ivy. So it may work, but I'm not sure it can be relied on.

Fri, Jul 31, 2009 : 2:16 p.m.

I would like to know where you found this information? I have looked through all of my foraging books and searched online but no where have I found anything about Jewel Weed seeds being edible. I found many sources that suggest using the juices from stalk to treat skin rashes, but none suggesting that any part of the plant is edible. I'm just curious.

Wed, Jul 29, 2009 : 7:40 p.m.

OOh, I can't WAIT to introduce the kids to this one. THANKS.

Jennifer Shikes Haines

Wed, Jul 29, 2009 : 4:45 p.m.

I never knew about these properties before. I can't wait to go trekking and find some. I think my son would love the exploding factor.

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Scientists discover how a common garden weed expels its seeds at record speeds

Plants use many strategies to disperse their seeds, but among the most fascinating are exploding seed pods. Scientists had assumed that the energy to power these explosions was generated through the seed pods deforming as they dried out, but in the case of ‘popping cress’ (Cardamine hirsuta) this turns out not to be so. These seed pods don’t wait to dry before they explode. A recent paper in the scientific journal Cell offers new insights into the biology and mechanics behind this process.

Several teams of scientists from different disciplines and countries including Oxford Mathematicians Alain Goriely and Derek Moulton and colleagues from Oxford’s departments of Plant Sciences, Zoology and Engineering and led by Angela Hay, a plant geneticist in the Department of Comparative Development and Genetics at the Max Planck Institute for Plant Breeding Research (MPIPZ), worked together to discover how the seed pods of popping cress explode. A rapid movement like this is rare among plants; since plants do not have muscles, most movements in the plant kingdom are extremely slow.

But the explosive shatter of popping cress pods is so fast that advanced high-speed cameras are needed to even see the explosion. Richard Bomphrey, of the Royal Veterinary College at the University of London, explains: “Because the seeds are so small, aerodynamic drag slows them down immediately.” To compensate, the seeds are accelerated away from the fruit and get up-to-speed extremely quickly. In fact, they accelerate from 0 to 10 metres per second in about half a millisecond, “which is super fast!” says Bomphrey.

Hay’s teams of scientists discovered that the secret to explosive acceleration in popping cress is the evolutionary innovation of a fruit wall that can store elastic energy through growth and expansion, and can rapidly release this energy at the right stage of development.

Previously, scientists had claimed that tension was generated by differential contraction of the inner and outer layers of the seed pod as it dried. So what puzzled the authors of the Cell paper was how popping cress pods exploded while green and hydrated, rather than brown and dry. Their surprising discovery was that hydrated cells in the outer layer of the seed pod actually used their internal pressure in order to contract and generate tension. The authors used a computational model of three-dimensional plant cells, to show that when these cells were pressurised, they expanded in depth while contracting in length, “like the way an air mattress expands in depth, when inflated, but contracts in width,” explains Richard Smith, a computer scientist at MPIPZ.

Another unexpected finding was how this energy was released. The authors found that the fruit wall wanted to coil along its length to release tension, but it had a curved cross-section preventing this. “This geometric constraint is also found in a toy called a slap bracelet,” explains Oxford Mathematics’s Derek Moulton. In both the toy and the seed pod, the cross-section first has to flatten before the tension is suddenly released by coiling. Unexpectedly, this mechanism relies on a unique cell wall geometry in the seed pod. As Moulton explains, “This wall is shaped like a hinge, which can open,” causing the fruit wall to flatten in cross-section and explosively coil.

According to Hay, their most exciting discovery was the evolutionary novelty of this hinged cell wall. They had evidence from genetics and mathematical modelling that this hinge was needed for explosive pod shatter, “but finding the hinge only in plants with explosive seed dispersal was the smoking gun,” says Hay.

These findings reinforce the description of evolution as a “tinkerer, not an engineer”, made by the scientist Francois Jacob. It appears that the sophisticated mechanism of explosive seed dispersal in popping cress evolved via tweaking the shape of already-existing cellular components.

When asked what implications their results will have for other researchers, Smith answered: “It is likely that other processes in plants that were previously attributed to passive shrinkage by drying are in fact active processes, especially in green, hydrated tissues.”

This study is a good example of how the recent trend towards interdisciplinary, collaborative science can lead to a global understanding of the biological and physical mechanisms at play in a complex process. The authors of this Cell paper built up a comprehensive picture of explosive seed dispersal by relating observations at the plant scale all the way down to the cellular and genetic scales, and systematically linking each scale. As Oxford Mathematics’s Alain Goriely says, “this approach was only made possible by combining state-of-the-art modelling techniques with biophysical measurements and biological experiments.”

The image above is of a mathematical model explaining the explosive dispersal of seeds from a common garden weed.

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