I recently received a call from a homeowner with a weed growing in her backyard that she couldn’t identify. Her neighbors had told her it was dangerous and she should burn it. She wanted to check in with Extension first. I had a guess after she told me it had white flower clusters and she lived on the river. I drove over to the Lakeshore area where her backyard was waterfront. I saw the pretty white flower clusters sticking out over the assorted grasses and Forbes that made up her yard and was afraid she might have a stand of water hemlock (Cicuta maculata), but I was still not sure. Looking closer, I saw the stems had purple streaks and the leaves were alternately placed along the stem. I cut into a stem. It was hollow inside. That’s when I knew it was water hemlock.

Water hemlock is one of the deadliest plants in the world

All parts of the plant are toxic and contain a chemical called cicutoxin. Within 30-60 minutes of ingestion, a person will experience nausea, vomiting, tremors, cramps, and convulsions. The most poisonous part of the plant is the root.

According to data from the CDC, from 1979 through 1988, at least 58 people died after ingesting a misidentified poisonous plant

There are a few plants that look a lot like water hemlock. One is Queen Ann’s lace (Daucus carota). This plant is in the carrot family and grows as a wildflower though it is not native to the United States. All parts of the plant are edible, cooked or raw. Flower clusters can be fried and have a carrot-like flavor. The stems are hairy, and the flower clusters have a dark purple bloom in the center. Another look-alike is elderberry. People often collect the fruit for use in pies and jams. It also grows on lake and pond shores and has white flower clusters. However, the inside of the stem is pithy and the leaves are arranged opposite each other along the stem.

I contacted a weed scientist and a botanist at the University of Florida to help me advise the homeowner. The weed scientist told me that complete eradication of this plant was going to be near impossible and the strategy could be to simply leave it alone. The plant is not harmful unless a person or animal eats it. The botanist agreed and noted that water hemlock is native to Florida and was growing by the river in its natural habitat. It serves as a host plant for the black swallowtail butterfly and provides nectar for numerous pollinators.

As I walked along the stand of hemlock, I couldn’t help but notice lots of bee activity and I did see caterpillars on one of them

My client has a dog, and while there are numerous reports of people and livestock being poisoned by water hemlock, there have been no reported cases with dogs. I reassured my client that it was not like poison ivy and touching it could not hurt you. To try to keep it from spreading, spot-treatments of herbicides can be applied. Systemic herbicides such as glyphosate or 2,4-D works best when applied in late spring and early summer. Plants growing in wet or submerged areas need to be treated with an herbicide specifically labeled for use in aquatic areas, if treatment is even needed.

Our native water hemlock provides nectar for pollinators and food for butterfly caterpillars

It poses no risk to people or pets as long as it is not eaten. Florida has many other plants that are commonly grown on purpose in our landscape that are also very toxic. Sago palm, oleander, and angel trumpet are the three that come to mind.
So, you can love and co-exist with a toxic plant when caution is taken.

Article written by UF/IFAS Duval County Extension Tonya Ashworth, Environmental Horticulture Agent July 2024

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