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Archive for September 2015

The Chemistry Behind Gardeners’ Woes

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Perhaps it is an innate response long imbued in my Homo sapiens genes or maybe my childhood penchant for thinking everything unrecognizable is poison ivy, but I was temporarily relieved of my embarrassingly poor plant identification skills this past week when my much more learn-ed coworker nearly unwittingly stepped into a massive patch of Virginia Creeper.

Virginia creeper

Virginia creeper growing on a chain-link fence outside my Yeadon apartment

“I can’t go in there,” he said with eyes wide. “I get terrible rashes from that plant.”

Rewind to a time before I started this current job in horticulture in Drexel Hill when I lived, utterly unemployed, in the basement of my sister’s boyfriend’s apartment further down in Delaware County in Ridley Park. Just next door lied the John Heinz National Wildlife Refuge at Tinicum, a restored wetlands filled with native milkweed, toadflax, and thistle as well as invasive garlic mustard (my favorite, savory cooking vegetable, nonetheless) and white poplar.

And then there’s the notorious Urtica dioica, or stinging nettle, lying in wait along the narrower paths of the refuge…

Cobbs Creek - Stinging Nettle

Stinging nettle in Cobb’s Creek; if you look closely, you can see the spiky trichomes on the plant’s main stem

Stinging nettle employs cleverly chemically armed outgrowths called trichomes, which contain pain- or numbness-inducing chemicals such as histamine and formic acid. The latter, if you know your Latin, is linked to ants, which naturally produce this carboxylic acid, otherwise known simply as ant venom.

But what does this have to do with my colleague’s fear of the creeper? While stinging nettle defends itself with those nasty trichomes, Virginia Creeper actually contains similarly but microscopically damaging structures within its leaves, called raphides.

Rashes caused by these oxylate crystals within Virginia Creeper can fool foliage-illiterate newbies like myself into misinterpreting red bumps for poison ivy or oak allergic reactions. But as the botanical name appropriately and helpfully describes (especially if you’ve taken some French classes), Parthenocissus quinquefolia is a five-leaved ground/wall cover, the sap of which causes skin irritation in certain sensitive (no offense meant) people. The crystals may also facilitate the introduction of other harmful chemicals into the skin within the same plant.

If your skin is now itching from reading about these unpleasant plants, look around for a plant with a somewhat translucent, succulent-like stem and a dangling orange flower (later in the season). Jewelweed, or Impatiens capensis, has been touted as a pain and itch reliever.

Many a website and personal account have claimed that the plant’s natural chemical, lawsone, is responsible for its anti-itching and -inflammatory effect. An NCBI search returned few studies on this subject, but a recent one strongly suggested that saponin, a soapy constituent found within jewelweed, may be effective in reducing inflammation from poison ivy and oak rashes.

Last week, I ventured into the nearby Cobb’s Creek, the westernmost border of Philadelphia proper, to pit jewelweed against nettle. Aside from an extraordinary amount of trash and raucous teenagers, the so-called park also has plenty of stinging nettle. I walked through a patch, letting it brush my legs, feeling a somewhat uncomfortable needling sensation that turned to a slight burning one then finally numbness. I cracked open some neighboring jewelweed (thankfully; I stupidly didn’t look for any before walking through the nettle) and spread it on my skin.

I’m not a firm believer in things in general; I still think my gluten allergy may have been a concerted scheme between my mother and doctor so I’d stop eating boxes of Triscuits every night. Whether it was the power of the mind/suggestive thinking or otherwise, I did feel immediate, near-complete relief from the prickling and burning sensations, while the numbness lingered.

Artemisia annua

Sweet Annie (Artemisia annua) and its soft, feathery, fragrant leaves which appear fluorescent green compared to other foliage

For now, the jury’s still out on jewelweed vs. Virginia creeper and stinging nettle, and I still find regular soap to be a better choice after contact with poison ivy (my coworkers and I carry with us a Tupperware container of Irish Spring). Even so, jewelweed, like its name, is a beautiful plant and is even cooler for its exploding seed dispersal mechanism.

Among other plants encountered on the job and which can cause rashes:

  • Wormwood — quite an extensive species, including my beloved and personal favorite, Sweet Annie (Artemisia annua), as well as Japanese yomogi (Artemisia princeps)
  • Mugwort — peanuts, several herbs (I currently have enough fennel to kill off the herbally sensitive population who happen upon my backyard patio)
  • Ilex — holly leaves contain saponins, bitter-tasting chemicals, and thwart the increasingly problematic herbivore of southeast Pennsylvania, deer! Albeit a fine defensive moat akin to barberry in the Philly and outlying regions for such grazing pests, it’s also the topiarist’s bane

Articles/Sources: (Jewelweed effects on poison ivy/oak) (Jewelweed’s saponin effects on poison ivy’s urushiol) (While focused on foraging for and cooking nettles, this article suggests using Aloe vera or dock [Rumex] to relive nettle stings)

Extra Special Interest: (Nettle. Eating. Contest.)