Well, then I guess you will have new plants next year.

Now I recall, Bidens torta is a non woody plant and only grows to three feet. I did look at Bidens species several times because the petal looks so similar. Plus, I think Porkpal said he went over them all too.

Just taking another guess...Verbesina?

I think Bubbles (Sandi) suggested Verbesina enceloides (Cowpen daisy) early on

http://www.wildflower.org/plan...

Thanks, I had not recognized it by the common name.

A picture of the seeds:

Here is Viguiera dentata seed from the wildflower center.
http://www.wildflower.org/gall...

Hmmm, I would say that is not a match. I will look for pictures of Bidens seeds.

Those are interesting looking seeds, are they hollow?

Bidens seeds should typically cling, aka Tickseed.
http://www.bing.com/images/sea...
http://luirig.altervista.org/p...

No, they do not look like Tickweed at all. They are somewhat cone-shaped but slightly angular. Now what?

http://theseedsite.co.uk/seedp...

Asteraceae family is a good start.

I looked at Asteraceae seed pods and nothing looks similar to these from the mystery plant.

Just for good measure I took a look at Geum seeds and they are not a match either.

I'm sure some of you are thinking this must be an imaginary plant!

I thought the seeds would make it easy. Yeah right.

There's two ways to find plants in Texas and more closely in your area.

Under dynamic tools select dynamic key, then select the family Asteraceae. Then click on the map where you are located, just above #69 south west of Houston. You will get a list of plants in the family for your area by clicking on 'build checklist'.

http://www.sernecportal.org/po...

The other way is to select Texas under State Floras, then go to the family but you get a lot more that way.

http://www.sernecportal.org/po...

Thanks, Janet. I'll follow that up.

We have to keep in mind that this may not be a native plant. It could have been brought by birds, animals or the wind from a source we don't know about, e.g. a garden hybrid plant. It doesn't look to be the type of seed which would be fed to birds.

I think you are right that it may have been introduced. I have never seen this plant anywhere except on my property. It is attractive enough that some previous resident may have planted it here. It originally grew only in one fence line, however, where there was unlikely to have ever been a flower bed; since then it has spread to unmown areas near that spot, spreading by seeds falling under each plant.
I think I will take specimens to some good local nurseries to see whether anyone recognizes it.

Look at Heliopsis.

http://grownative.org/wp-conte...
http://grownative.org/native-p...

http://www.namethatplant.net/p...

There's similarity to Verbesina ..

http://www.namethatplant.net/g... bracts of DYCs with ray and disc flowers

You need to click on the lower right link on the last link of Christine's to get the "compare involucral bracts of DYCs with ray and disc flowers", the above link doesn't work.

The leaves of Verbesina encelioides are the closest match yet, I can't open the link as there's a problem with the site security.

http://newfs.s3.amazonaws.com/...

https://www.google.co.uk/searc...

The flowers and seeds don't match, I wonder if it's a cross between this species and another.

http://keyserver.lucidcentral....

Heliopsis has several similarities, but the leaves are said to be all opposite, while my plant's are mostly alternate. My plant also lacks the developing ovary at the base of the rays as pictured.