PlantFiles: Ragweed Parthenium, White Top, False Ragweed
Parthenium hysterophorus

This plant is growing like mad in an area of my horse pasture, and one of my donkeys was chowing down on it, which is what led me to want to find out what it is (and if it was poisonous or not). Like the other poster, it took FOREVER to figure out what this was. My sister and I have been searching online off and on for two days now!

Today we finally were able to narrow down to a hunch that it was in the Asteraceae family, then we found a site that listed the Parthenium genus plants. Voila, we saw a photo of False Ragweed, but the photo wasn't very good. FINALLY, we did a search and found it was listed here on Dave's.

Thank heavens for this site. It was beginning to drive us nuts!
Thank you everyone who posted pictures of it, too!

For us, we had no allergic reactions. We have been handling them quite a bit these last few days, so if we were going to we'd be in pretty bad shape as much as we've handled and sniffed, etc.

I'm wondering if perhaps the Texas variety is not as noxious as the ones elsewhere...?

I'm in Spicewood btw. I think my membership here says Brownwood, but I've moved. Spicewood, TX is outside of Austin.

It took quite a while for me to find the name of this pretty plant. I found it growing on the side of the street and planted it in my yard. It was beautiful all year. This spring I had about 6 seedlings to come up near where it was planted. I removed them and planted them where I wanted. It has tiny white pentagon shaped flowers and the large plant is covered in the tiny flowers causing it to look like Baby's Breath at a distance. Apparently, Im not allergic to it. It is care free in my garden and fits well with my plan of xeriscaping.

A terribly invasive weed - make sure to deadhead, otherwise it'll take over your garden.
It has taken over millions of acres of land in India and Brazil and choked out native plants and even crops. Causes allergic reactions.

One of my favorite plants - this is really one of those wow plants you just love in the native garden. Very carefree and does not need a lot of water to bring out the huge white blooms.

This plant is native to Texas, it is an annual about 3 feet tall.
Blooms June- October in zone 8, I find this plant very atractive, the leaves are lovely and the flowers small and delicate.
I find that I am not allergic to it, so I recommend growing it as an ornamental native.

It is one of the worst weeds that I have come across. In the rainy season when the plants bloom, the pollen from the flowers cause respiratory allergies in some people esp. in areas where the growth of this weed is abundant and uncontrolled. (Homeopathically, it is used as a medicine to cure such problems). It has the great ability to reseed. It is said that it appeared in India somewhere in the '70s with American wheat that India imported. It later spread all over the country and was a major problem in agriculture. So invasive it is! Scientists had found that a particular beetle was fond of its leaves and they had left them in areas where it was to be eradicated. It worked but that beetle began to eat away other plants and that was withdrawn.