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Weeds of Mystery



I’d planned to make this post a paeon to more of the weeds I enjoy (I’ve already gone on at length about chickweed and miner’s lettuce).

But, as so often happens, the post decided to go in another direction.

I identified my first weed, henbit, pretty easily, as I do every year. I seem to have a block where the name of henbit is concerned, though I did somehow remember it’s a Lamium.

I looked it up where I usually do, an ancient pamphlet from an herbicide company, identifying common weeds.

Just to check (the pamphlet pictures weren’t all that good to start with, and a few decades on the shelf hasn’t helped) I went online and found not only henbit but another weed whose identity had been puzzling me. It turned out to be Geranium carolinianum, Carolina geranium.  Now I’d identified two of them, I toyed with the notion of just leaving the mystery weed out, and doing a post on henbit and Carolina geranium, plus a couple of others I know.

The U of Arkansas weed index is a very sensible grid, easy to use: thumbnail photo with common name, scientific name, weed type, and life cycle (whether it’s annual or perennial, and what its season is).  Since it’s not very long, it’s quickly searchable, and you can print a .pdf version if you want. It does have a lot of the most common weeds you’d find in a garden, a sort of improved version of my old herbicide pamphlet.

I’d found two of my nameless plants, but I was obsessed with the notion of identifying the little white-flowered weed.  I’d  vaguely thought it was shepherd’s purse. A close look at the shepherd’s purse photo here proved that it definitely wasn’t: the leaves were the wrong shape and size, both on the flowering stems, where they were thin and vaguely spade-shaped



and at the bottom rosettes, where they were rounded and no more than 1/4 inch (a little over half a centimeter) wide, as you can see in the picture at the top of this post. And the flower heads were tiny clusters, not the spikes of shepherd’s purse.


I was on a roll, now; I thought I’d see what other university weed identification sites had to offer. Since I live in northern California, I thought I’d check out the Davis weed i.d. site first. Weeds are usually imports that spread themselves generously – that’s why they’re weeds – so it’s not as vital to look for a university that’s in your area as it might be for, say, tree identification. Weeds are mostly associated with agriculture and gardens and other places where humans have set a heavy foot. A great many of the commonest weeds are Europeans, who, like their human counterparts, set foot on this country and decided to take it over where they could.

But I know that UC Davis has one of the best ag departments in the country, and it seemed a good bet that if there was a weed common in Northern California, they’d have it on their site, whether it was native or not.

I knew it was likely that my weed was an import, and I knew for a fact that imported weeds can do well in California. My horticulture teacher told of one of the more successful weed invasions. I had always assumed that the Himalayan blackberries you see all over northern California (not to mention large tracts of Washington) were a pestiferous native. (I never understood why they were called “Himalayan”, and I think it’s an insult to the Himalayas.) Himalayan blackberries are the huge thorny tentacley shrubs that take over entire fields and can cover dirt roads in a few years.  We have special methods of weed control just for them.

But, my horticulture teacher said, he’d found  a book published in the 1940s that discussed Californian blackberries, and the kind we call Himalayan, it said, were rarely-found imports. Just goes to show how far a weed can go in a few decades. Removing the triffid-like tangles of “Himalayan” blackberries was a business opportunity by the 1970s.

Anyway, I headed over to the University of California Davis site, to see what I could see.

The UC Davis website is a much more sophisticated setup than the Arkansas one. It asks questions on a little multiple-choice questionnaire to guide you to your plant, kind of like an automated key. Knowing some botanical terms, such as leaf arrangements and venation type, is useful, but there are also questions anyone can answer: what kind of lanscape you found it in, what color the flowers are, whether it has prickles or hair. They remind you that a few right answers are better than a lot of “I’m not sure” ones.

Then you get a selection of images that might match your plant. If it had worked better for me, I’d be more enthusiastic about it, because it’s much handier than just going through a list and hoping you’ll find the right thing.

But it didn’t work for me. I got Italian arum, which doesn’t look anything like my weed. (Can anybody out there identify it yet?)

Next post, the story continues: On the Trail of the Mystery Weed

{ 13 comments… add one }

  • Brent March 19, 2010, 2:41 pm

    Your unknown looks like Cardamine oligosperma, bittercress or little western bittercress, or Idaho bittercress.

    It’s actually native to California (as well as elsewhere in N. America) and quite common in planting mixes / nursery plants as I recently discovered.

  • Helen at Toronto Gardens March 19, 2010, 5:47 pm

    Brent’s comment would have been mine, had I replied sooner. Have a look at this site:


    Four petals usually is a tip-off that it’s in the mustard family (just like 4-sided stems say mint family). So I did a search for “white flower mustard family california” and this link showed up.

  • lostlandscape (James) March 20, 2010, 9:51 am

    I sign on to mustard, too. Last weekend in the desert we went a little crazy separating out the good from the bad–a small California mustard (good), Saharan mustard (evil), a couple others…

  • jodi (bloomingwriter) March 22, 2010, 3:25 am

    Add me to the mustard/cardamine vote. We all get different weeds, of course, and identifying them can be a challenge. Thank you for putting me onto the U of Ark. site. I’ll have a lot of fun getting to know more about botany elsewhere.

  • Frances March 22, 2010, 5:20 am

    It is the bitter cress, as noted. The flowers are pretty, in an innocent oh let me live here I won’t hurt anything kind of way. BUT, what happens is the foliage becomes larger and larger, even after the seeds have been released, shading out other more worthy seedlings and or emerging perennials. It is what we refer to as born pregnant, for by the time you notice the flowers, the seeds have already been spread. We are in the process of digging it wherever it is found at the moment. Must be quick with the tool to get the whole thing. :-)

  • Pomona Belvedere March 22, 2010, 9:33 am

    You’re all much smarter than I am, weed-wise; thanks for the i.d. and tips. However, I’m going to post the next article anyway, since I went to a few more great weed-identifying sites (not great enough to identify this weed as exactly as you, Brent. I didn’t know there was a native bittercress.)

    Thanks for contributing that site, Helen. Another good one.

    Nice to hear from you, jodi. I always learn cool things from your posts, glad I can reciprocate a bit.

    Frances, I will watch out for those leaves!

  • Pomona Belvedere March 22, 2010, 9:34 am

    James, I forgot to comment on your Star Wars for mustards! That’s an interesting task to take on. This time of year, we have lots of formerly-known-as-cruciferae blooming up in northern Cal. I don’t know which are pestiferous; are you doing a post on that?

  • Meredith March 23, 2010, 11:05 am

    Pomona, thanks for posting this. I am not too savvy with the names of weeds yet; I generally just know if it’s not what I meant to plant there, and that’s been enough info to be going on with. 😉 But I am beginning to learn their names and why they might prefer my potager to other spots, and so now I can add bitter cress to my list of known weeds. I recognized it right away from your lovely pics and its terrible habit of coming up among the eggplants.

  • Pomona Belvedere March 23, 2010, 2:19 pm

    Hm, I didn’t know eggplants were a favorite of bitter cress..I wonder, is this some version of companion planting, where the plants choose their companions?

  • Barbee' March 24, 2010, 3:36 pm

    Yikes! You ID’d one for me! That Carolina Geranium is spreading here, and I didn’t know what it is. I did say it looked like a wild geranium, but it wasn’t the wild, pretty Crane’s Bill geranium that I like. Thank you.

  • Pomona Belvedere March 25, 2010, 5:02 pm

    Barbee, I’m so glad I was able to help you identify Carolina geranium. That was good detective work on your part, since I wound up not posting photos of it!

  • Barbee' May 11, 2010, 1:24 pm

    Pomona, it is so amusing that I had read this post and even left the above comment, but did not recognize the Cardamine oligosperma from the photos here. Thank you for checking out my post and telling me what it is. You helped me again.

  • Eric October 24, 2015, 12:08 pm

    past two years I’ve celebrated our house’s anvnseriary. You can read them here and here. So I only thought it fitting to continue the tradition into year three. But this time

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