Another stupid herbaceous weed

[Dodgy Loner]

I've got a vegetable farmer in my county who's having some serious problems with this weed.  We need to identify it, so we can figure out how to control it.  Here's the lowdown:

Prostrate, spreading herbaceous annual.
Leaf shape - elliptical
     length - 1.5-2.5"
     width - 0.5-1"
     arrangement - opposite
     venation - pinnate
     margins - smooth or very slightly toothed
Roots are fibrous, and the plant reproduces by dropping adventitious roots from lateral nodes.
Stems are round in cross-section, fleshy, pink-purple at the roots and green near the leaves, with prominent longitudinal veins encircling the perimeter.
Small hairs are present on the stems and leaves, but they are not prominent.
No flowers or fruits were present.

I feel like I'm writing a "Wanted" poster .  Here's what the culprit looks like (The plant is quite wilted at this point):

[Timburr]

Without the flower, the nearest I can get from being so far away is epilobium.... or valerianella.... .   Are the leaves hairy?

Is there a "reward" for the offender's identification? 

[Tom]

http://www.abctlc.com/courses/WEEDS.pdf

Just a link to keep in your pocket. 

[WDH]

E-mail me the pics and I know someone who likely can ID it.

[SwampDonkey]

If it exudes milky sap, I would suggest spreading dogbane Apocynum androsaemifolium

[Dodgy Loner]

Is there a "reward" for the offender's identification? 

My appreciation ?

I can't rule out any of the genera that have been suggested, but I haven't found any species that match.  This plant is very low-growing, less than 6" tall, and most of the species in the suggested genera are upright plants.  The leaves are not noticeably hairy.

[Tom]

My first thought was on of the wandering jews, but, it doesn't quite fit the bill.

[woodbowl]

Sounds kinda like pusley.

[Dodgy Loner]

The growth habit is nearly identical to wandering Jew, but wandering Jew is a monocot, whereas this plant is a dicot.

[SwampDonkey]

Yeah, doesn't really fit spreading dogbane either.

Are the leaves aromatic? Your quite limited by oppositely arranged and elliptical leaf shape. Most are pubescent and aromatic and often square stemmed and serrate leaf margins.

Your plant is almost a cross with a pea and a clover. 

Something in the chickweed family? The leaves look bigger than most chickweed species.

Sometimes an Ag department puts out a good weed booklet. You can do stuff online, but it's too slow a process on dial-up.

[Dodgy Loner]

I work for the ag department!   I'm a agriculture & natural resources extension agent.  I've found that every resource for weed ID is incomplete.  There are just too many of them!  I guess I really need the flowers or fruit to narrow it down, but I can't exactly tell the farmer that he needs to let the weeds mature and put out seeds before he does something about it .

[SwampDonkey]

Yeah that's the dilemma, too many weeds and a lot of alien ones. 

[SwampDonkey]

Dodgy, I believe I've seen that very weed here before.

[SwampDonkey]

 

Look familiar Dodgy?


Bladder Campion: Silene vulgaris  "Pink Family"

This has a pink/purple stem down at the base.

Seems very resistant to herbicide, crop rotation and intensive summerfallow is recommended by U of Manitoba.

[Dodgy Loner]

Looks very familiar, but I'm still not sure they match.  Bladder campion has a sessile leaf, whereas the plant I've found has a small but noticeable petiole .

I'm heading back out to the field today to see if I can turn up any specimens with flowers.  If it is bladder campion, the flowers should make it easy to tell.

[SwampDonkey]

Does a fresh sample have a white sheen on the stem and leaves that is easily rubbed off?

The leaves are not always clasping, sometimes on very short petioles on basal leaves. It sure is a close one  if it's not a match. Must be a relative and I bet as hard to be rid of in fields.

There are 8 -10 other campion species which are very similar to bladder, but most are hairy (white campion) and some have sticky hairs, known at Catchfly.

[WDH]

Dodgy,

Here is the response that I got back from our Botanist:

Danny,

I was making this too hard.  I was forgetting what now seems to be the obvious.  I am 99% sure that it is alligator weed.  Amaranthaceae - Alternanthera philoxeroides.  A warm climate aquatic invasive from South America.  Vary prolific here in Louisiana.  Rather variable leaf shape, from oblong to narrowly elliptic to elliptic to obovate.  Edges of ponds, lakes, and streams and in wet ditches and mud flats.

Don't tell Al Gore.  He would consider it conclusive proof of global warming that this plant has moved its way up into the north Georgia Mountains.

Running this by the Louisiana Heritage botanist to get that last 1%.  He specializes in aquatics.

Here is a weblink:

http://plants.usda.gov/java/profile?symbol=ALPH

Is your clients site either low ground or wet?

Also, here is a good image library for vascular plants: http://www.csdl.tamu.edu/FLORA/gallery.htm

[Dodgy Loner]

Thanks a lot, WDH.  I have an encyclopedia of North American weeds and keyed it down to alligatorweed and common purslane.  I knew it wasn't purslane, which has leaves are too small and fleshy to match the plant I found.  I had ruled out alligatorweed because it's supposed to occur in wet locations.  Although the field this plant came from is irrigated, it is definitely not "low" or "wet".  I'll check with our weed specialist for recommendations on control.

[Dodgy Loner]

The link to the photo library you posted is great, by the way.  This is the type of habitat that most sources post for alligatorweed.



The photo library had this pic in it, which is a lot more like what I saw:

[SwampDonkey]

Wow, what a weed. Good luck to the farmer to be rid of it.