"White snakeroot (Ageratina altissima) is highly poisonous because all parts of the plant contain tremetol, a fat‑soluble toxin that can cause severe illness or death in humans and animals, especially through contaminated milk. The toxin remains active even when the plant is dried, making hay contamination dangerous.

It is Highly poisonous to humans and livestock: Tremetol causes “milk sickness” when humans consume milk from animals that have eaten the plant. This illness historically caused many deaths, including that of Abraham Lincoln’s mother." Many sites list White Snake Root as "one the top 10 most toxic flowering plants in the world. Poisoning symptoms often appear several hours after ingestion and may progress over days. As poisoning advances, there is muscle coordination loss and ataxia, stupor or coma, dehydration from vomiting and poor intake. Death typically occurs 2–10 days after symptom onset."

White snakeroot is a native plant that is responsible for killing thousands of people in the Midwest and eastern United States in the 18th and 19th centuries. It killed thousands of cattle and horses, too. However, on a positive side, pollinators love the flowers.

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I found the above growing camouflaged in with one of my potted hibiscuses on the deck. Both have a very similar shaped leaf. The sudden appearance of the white flowers, however, made me do a double take of the second shoot that was 3' tall & growing with its leaves intertwined with the hibiscus. This was just one of about 2 dozen flower cluster. To say the least, White Snake Root is definitely one accidental weed volunteer that has to go!!! I have always been very careful to select only non-toxic and dog safe plants to grow. Unfortunately, this sneaky volunteer got past me.
Fortunately, I discovered it before Tara did.