Janet, your links do seem to confirm Sooby's ID. Are you not certain still? I will ask the extension agent whether he agrees. I do think that you folks have solved the mystery.

I just saw your last post, Janet, and I believe that comparison completes the ID. Many thanks to all!

Wow, just when one thinks all hope is lost Sue comes through & Janet concurs.
Porkpal, you have to put this one in the db for sure and a comment as well - maybe linking back to this thread so people can see how it was verified.

Sill, the problem of what about the horses but at least now you've eliminated this.

I am amazed and grateful at all the efforts that went into to solving his mystery, and I will add it to the data base. Thank you all again!

Great ending!

Fantastic identification. Best mystery plant ever!

Have they checked the field for Trifolium hybridum aka Alsike Clover or Swedish Clover; it can contribute to liver disease in horses but don't know if it grows in your area of might have been included in hay bales at some point in time.
http://www.tsln.com/agliving/e...

Don't ya all love a good mystery.

I went through the available yellow Asteraceae on the Texas wildflower site but I probably got thrown by the leaves, good for Sue on picking it out.

Greene, we have checked the field and there is no clover; I don't think I've ever seen Alsike clover in this area. Also I was not feeding hay when these two horses became ill. The ag. agent did say that any of the plants in the sunflower family can be toxic if eaten in sufficient quantity; so I suppose "The Plant" could have been the culprit - maybe.

Brava Sue. Great job.

Thanks Jean and everyone. I just hope the equine aspect can be resolved. I hope you will keep us updated, Porkpal?

sooby said:Thanks Jean and everyone. I just hope the equine aspect can be resolved. I hope you will keep us updated, Porkpal?

I have asked the ag. extension agent whether this plant could have caused the liver damage. Meanwhile the horses are doing better, so they will probably make a full recovery - eventually.

You people are amazing. None of the botanical experts could identify the plant, but with remarkable perseverance you made it happen. I feel like we should have a party or something!

Even my DH was impressed that so many people chimed in to help ID your plant, porkpal! Glad it wasn't the one that made the horses sick. Now you still have a mystery to mull over this winter.

Party!! Yes, make a big batch of chili and we will all be over to help you eat it. It may take a while for everyone to arrive as people in three countries were involved in this solving this mystery.

I think that sooby/Sue and JRsbugs/Janet Super Sleuth are some pretty good botanical experts.
With all the folks adding their suggestions and helping to eliminate plants it all works to get us to the one correct answer. I really hope your horses will make a full recovery. Maybe when they are looking more fit you could take some photos and post them?

Will do! (you want beans with that chili?)

I vote for beans! But you Texans don't consider it chili if it has beans do you?

Congratulations to Sooby and Janet on some brilliant sleuthing It's been a fun thread. Hope the horses make a full and speedy recovery.

Porkpal, I know you must have checked this but just in case.......
I happened to be researching lambs quarters - Chenopodium and ran across this:
"Grazing animals will eat common lambsquarters when young, but as it matures it becomes woody and disagreeable. Under certain conditions, it can also accumulate nitrate, sulfate, and oxalates in its tissues and cause poisoning of livestock if eaten in large quantities."
From:
https://extension.usu.edu/weed...

I don't have any idea if any of that could cause liver problems in horses but wanted to mention it.

Thank you. I have never seen lambs quarters growing in any of our pastures, but it is good to be aware.

I am pretty sure that the innocent seeming Mystery plant, now that it has been identified as Sclerocarpus uniserialis, a member of the sunflower family, is actually the culprit. The extension agent said that all the members of the sunflower family can be toxic to the liver if eaten in large enough quantities. This plant grows (grew) heavily in the fence line of the pasture in which these two horses were living and in none of the other pastures. I needed to work on the fence so I pulled it all up and put it in the burn pile which was also in that pasture. The horses, who had never eaten it before, now considered it a treat and ate an unknown quantity of it. They fell ill shortly afterward. The timing of the events is what made me suspect the plant and want to identify it.

I am still awe struck by the effort you all put into helping me and am very impressed with your success. I also learned a lot. Many thanks!

All's well that ends well! I am so happy to hear that you're pretty sure the mystery plant was the culprit & that the horses are healing.

This thread has really opened my eyes. I had no idea so many plants could be toxic to some degree or another to livestock. I knew about wild black cherry but not about anything else. Not that I have livestock or am ever likely to but I do have neighbors with livestock and I would not wish to plant anything that might get into their pastures and harm their cows or horses or donkeys.