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oralee 11-08-2015 03:06 PM

Is this native or invasive? Looks like water smart weed?
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I have been unable to identify this plant that seems to be increasing in patches in my 2-acre back yard. Should I get rid of this or encourage it?

The plant looks similar to online pictures of "water smart weed" (polygonum amphibium) but to my knowledge has never flowered.

More information----------------------------

The plants are in a “wild” field overrun with invasive weeds, so I do not believe the plants to have been deliberately planted by people, but wild volunteers from wild origins. The field is in western Santa Rosa, clay soil, no trees/just full sun, and summer dry dry dry. There is a "channelized" creek a hundred feet or so away behind our fenceline.

I have attached a few photos, but also here is a description of the plant:
1-2’ high growing in a loose “ground-cover” habit. Sprawling, woody stems with upright ends; leaves appear along the entire length of the stems (which can be from a few inches to a couple of feet long). The leaves are approx. 2-4 inches with smooth (sometimes wavy) margins, pointed tips, slightly fuzzy tops, and arranged neither opposite or alternating but perhaps “whorled” or random arrangement along the stems. Overall the leaves appear bright to dark true green, and can appear to sparkle a bit in the sun from the fuzzy tops.

The leaves turn yellow or brown in fall and the whole plants dry up and disappear over the winter. I have not ever seen any flowering or fruiting structures, but have not closely observed the plants in spring when they tend to be buried in the invasive harding grass we have growing everywhere. ;) I only notice the plants after we mow the field in the summer, and they don’t really seem to do anything except expand with new little plants popping up everywhere along the edges. The plants stand out in the summer when everything else is dry/brown and only this plant stays bright green and fresh looking. Roots might be tuberous (appear thickened and horizontal) and I suspect the plant is propagating by underground runners.

Thanks to any insights, this has been driving me nuts for years.

terrestrial_man 11-11-2015 11:01 PM

I would agree that it is a Polygonum species but not P. amphibium. I have P. amphibium growing in my yard and it does not look like the one in your yard. Yours has leaves that appear to be almost leathery looking. Also since it is growing in a meadow and gets dry and comes back, if it was P. amphibium you would be seeing small terminal flower spikes with small white flowers as it tends to be an annual to a biennial and once the stems die they do not revive. Only new seedlings grow. Just checked my plants and what I have are older plants starting to die off with flowers having set seed and younger plants. Leaves are thin but if grown emmersed they can be more succulent in appearance.
There are many species, 14 non-natives and 22 native species, found in California. Have you seen the plant anywhere else? If not then I would opt for native and check them out first. Here is a link to the USDA plant database.
Be sure to click SHOW ALL and scroll down to the bottom to see the distribution of the species in the USA.
You can also check the CalFlora page and click on the species links and maybe there will be images of those you can look at. Here is that link:
Good luck.

oralee 12-17-2015 06:21 PM

Thanks for your help
Terrestrial man, thank you for taking the time to help me with my puzzle! I seem to go in circles online - I checked out the pages you linked, and polygonum (persicaria) amphibium descriptions seem to match my backyard plant (except mine haven't flowered) - however images seem to vary greatly. Some look just like what I have while other images look so different.
By now all my plants have withered up from the cold, so I will try to see them again this spring...(-:
Do your smartweed plants have moisture during the summer? I have the theory that my plants look more "leathery" because they get no summer water.
Enjoy the holidays.

terrestrial_man 01-14-2016 10:16 PM

oralee, sorry about responding so late. But I treat the Polygonum as an aquatic species and so it wet most of the time. It generally dies back but I have just looked to see what I could find (910PM) and there is one with a just a red lead at its tip as showing the effects of the cold weather but the base of the plant is protected by a large rock and a large pot and has a few young growths that are still green. With adequate water the stems are somewhat succulent. Drier and they become scraggy. Leaf size is also affected by the amount of water the plant has access to.

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