Toxic and toothsome: a tale of two wild Asteraceae

Toxic Interloper:

Not long ago, I planted a bunch of coriander/cilantro seeds in my back yard.  When the seedlings emerged, I found not only cilantro, but also this:

Not cilantro as it should have been, but common groundsel. Don’t try to fool me with your toothed leaves–I can totally see you’re sending up flower buds already.

Senecio vulgaris, known as common groundsel to me, but also as Old-man-of-the-spring. It’s just about everywhere right now–I’m seeing it along roadsides, in gardens, at the park and clawing its way through sidewalk tiles.  It starts off with lobed leaves and an emerging crown of flower buds that’s visible really early, and ends up with nearly-closed yellow flowers, and fuzzy gray seed heads like tiny dandelions (whence the “Old man” name–it looks a bit like a tousled gray head of hair).

Mature common groundsel plant, hanging off the edge of the planter. You can see several of the yellow flowers at its far end.  Sorry this is kind of a dreadful picture–click on the “Senecio vulgaris” hyperlink above for better ones.

A closer look at the mature flower heads, and an immature seed head at the top left.

Common groundsel has been used medicinally throughout history, but rides a fine line between beneficial and noxious.  Like its relative tansy (Tanacetum vulgare), it has been used to promote menstruation (and as an abortifacient–right, George RR Martin fans?), and like its relative wormwood (our absinthe-flavoring buddy), it has been used as an antihelmintic (de-wormer).  But just like wormwood, it can wreak havoc on your liver if consumed in high doses over a long period of time.

Because common groundsel is only toxic with chronic consumption, most of the literature about groundsel toxicity pertains to livestock–grazing animals are vulnerable when it’s prevalent in the fields where they routinely eat.  But there are also a few cases of people repeatedly drinking tea made with common groundsel who have then developed hepatic veno-occlusive disease, where the veins of the liver are blocked by damaged tissue and don’t drain properly. Groundsel is probably worth watching out for among your herb and vegetable beds, since, like I said, it’s pretty ubiquitous, and looks a lot like some edible greens.

A friendlier family member:

Although herbs like common groundsel and wormwood are not always user-friendly, many others of the asteraceae are.  Chamomile, dandelions, sunflowers, many types of lettuce…these all make welcome appearances in our food.  (For a lovely sampling of asteraceae on the other side of the globe, check out Theobrominated’s post here).  Wild asteraceae can also be benevolent (Nature’s Garden has a whole chapter devoted to them), like sow thistle, chicory, and this guy:

Pineapple weed, North American native and a tiny snack for everyone!

Pineapple weed (Matricaria discoidea) is one of my favorite forage-ables from childhood.  It doesn’t provide a very filling meal, but the little flower heads offer a fun texture (a bit like a very tiny broccoli crown) and sure enough, they do taste surprisingly of pineapple.  We recently found these growing abundantly at Point Isabelle, but I expect you could find them anywhere grassy and sunny.  Look for a low-lying plant (6-8″ high) with lots of greeny-yellow flower heads the size of pencil erasers.

I think the asteraceae, like the apiaceae, represent a useful reminder that it’s a really bad idea to overgeneralize, even among closely-related plants.  Two very similar-looking plants of the same family, or even genus, can have quite different properties.  What’s more, the very same plant can be good for you and bad for you, depending on how much you eat.  Wikipedia made a point of this in talking about S. vulgaris–how there was this controversy over whether it was medicinal or toxic.  But that’s a bit contrived–it’s essentially just a much less dramatic case of the same thing we take in stride with Digitalis or Atropa: that a plant alkaloid can be super toxic if you gobble it by the handful, but has its place in medicine when taken for the right condition in small doses.

Extra Nitty-Gritty: Senecionine

In common groundsel, the liver toxicity culprit is a pyrrolizidine alkaloid called senecionine, whereas in wormwood and tansy, it’s thujone (just to be confusing, another relative, tansy ragwort, is also in the Senecio genus and expresses senecionine).

Senecionine, the molecule responsible for hepatotoxicity of common groundsel, and related plants like tansy ragwort.

Senecionine is one of several plant-derived pyrrolizidine alkaloids that cause hepatotoxity.  They come from a range of plants, and have variable kinetics: some are only mildly toxic, some are more severe, some act slower and others faster, all according to their metabolism (the toxicity derives not so much from the initial alkaloid itself, but rather the highly-reactive products it’s metabolized into, some of which can cause tissue damage, or even directly react with DNA, causing mutations and potentially cancer). Although it takes a long buildup of senecionine to cause liver damage, once that threshold is reached it turns out to be pretty toxic.  When authors of a recent article compared senecionine with another pyrrolizidine alkaloid, adonifoline, they found that senecionine is rapidly metabolized by cytochrome p450.  They suspect that the rapid accumulation of damaging metabolic byproducts (some of which can alkylate DNA and cause tumors) may be responsible for senecionine’s comparatively high toxicity.

For the curious, here’s the reference for the senecionine toxicity paper:

Wang, C., Li, Y., Gao, J., He, Y., Xiong, A., Yang, L., Cheng, X., Ma, Y., & Wang, Z. (2011). The comparative pharmacokinetics of two pyrrolizidine alkaloids, senecionine and adonifoline, and their main metabolites in rats after intravenous and oral administration by UPLC/ESIMS Analytical and Bioanalytical Chemistry, 401 (1), 275-287 DOI: 10.1007/s00216-011-5075-3

ResearchBlogging.org

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6 thoughts on “Toxic and toothsome: a tale of two wild Asteraceae

  1. I think I need to have a Pocket Andrea to help me decide what’s edible and what’s not. 🙂 Speaking of… we saw some berries last week and weren’t sure if they were edible! JY proceeded to eat one and he seemed OK, so I guess that answers that question. It looked like a raspberry but brighter and rounder? I’ll show you a pic next time I see you.

    • Maybe a thimbleberry? We saw some at redwood regional a couple weeks ago that were getting close to ripe. They’re really yummy! Ooh–and the wild strawberries are ripe now too–we should go for a return forage once I’m back from MBL!

  2. I was surprised to see the pineapple weed described as a “North American native,” as it shows up in my San Diego Count Native Plants book as “non-native.” Calflora also says it is not native to California. So the question is, where in North America is it native? Wikipedia seems to think it is “native” all the way down to Baja….

    But thanks for letting me know it’s edible! I didn’t know.

    • This is useful: http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=242331665

      “It is a northwestern North American native that has spread to eastern and northern North America and elsewhere (E. McClintock 1993b; E. G. Voss 1972–1996, vol. 3; A. Cronquist 1994). NatureServe (www.natureserve.org) and Natural Resources Conservation Service (plants.usda.gov) erroneously present M. discoidea as introduced on the continent. Its natural habitat is ill-defined because the species has become ruderal even in its native range.”

  3. Pingback: Fall Flower: Chicory | GreenHawks Media

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