Poison Hemlock, Spotted Hemlock, Poison Parsley, California Fern, Nebraska Fern, Deadly Hemlock, Poison Fool’s Parsley, Winter Fern

Conium maculatum

koh-NI-um mak-yuh-LAH-tum

Synonyms of Conium maculatum (23) (Updated on 11-12-23 from Plants of the World Online): Cicuta major Lam. (1779), Cicuta officinalis Crantz (1767), Conium ceretanum Sennen (1926 publ. 1927), Conium cicuta (Crantz) Neck. (1768), Conium croaticum Waldst. & Kit. ex Willd. (1809), Conium leiocarpum (Boiss.) Stapf (1886), Conium maculatum var. barceloi O.Bolòs & Vigo (1974), Conium maculatum subsp. croaticum (Waldst. & Kit. ex Willd.) Drude (1898), Conium maculatum var. immaculatum Schur (1866), Conium maculatum subsp. leiocarpum (Boiss.) Drude (1898),Conium maculatum var. leiocarpum Boiss. (1872), Conium maculatum var. viride DC. (1830), Conium maculatum subsp. viride (DC.) Espeut (2002), Conium maculosum Pall. (1771), Conium nodosum Fisch. ex Steud. (1821),Conium pyrenaicum Sennen & Elías (1928), Conium sibiricum Steud. (1840), Conium strictum Tratt. (1811), Conium tenuifolium Mill. (1768), Coriandrum cicuta Crantz (1762), Coriandrum maculatum (L.) Roth (1788), Selinum conium E.H.L.Krause (1904), Sium conium Vest (1805)

Conium maculatum L. is the accepted scientific name for the Poison Hemlock. The genus and species name were named and described as such by Carl von Linnaeus in the first volume of the first edition of Species Plantarum in 1753.

As of 11-12-12 when this page was last updated, Plants of the World Online by Kew lists 6 species in the Conium genus. It is a member of the plant family Apiaceae with 447 genera. Those numbers could change as updates are made on POWO. 

The above distribution map for Conium maculatum is from Plants of the World Online. Areas in green are where the species is native and purple are where it has been introduced. The map on the USDA Plants Database for the United States and Canada is similar.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

THERE ARE SEVERAL LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND TO HELP WITH A POSITIVE ID.

I have been seeing the Conium maculatum growing along the highways and backroads for several years but never stopped to take photographs. Mainly because I didn’t have my camera and I don’t have a cell phone. Then on April 29 in 2022, I was mushroom hunting along the fence (actually across the fence) when I spotted a small plant that looked suspicious that had been mowed off and grown back. I had my camera so I took several photos and uploaded them on iNaturalist. Sure enough, it was a Conium maculatum…

Then, a few days later, I found a fairly large plant right under my nose behind the barn… I decided to let it grow to take more photos after it started flowering. I thought I could cut it down after that, but the man (also a good friend) who leases the farm for hay cut it down and baled it up… I told him about the plant.

There were more behind the barn in 2023…

Conium maculatum is a biennial species native to Eurasia. It can be found throughout Missouri and most of North America and is easily identified by being a large plant and its ferny leaves and large umbels of white flowers. It is also known as the species that killed Socrates (and many others)… Common names include Hemlock, Poison Hemlock, Spotted Hemlock, Poison Parsley, California Fern, Nebraska Fern, Poison Fool’s Parsley, Winter Fern, and possibly others.

Conium maculatum prefers growing in full sun in fairly moist soil in poorly draining soil. They can be found along ditches, pond banks, in low areas in pastures, barn lots, along woodland borders, along highways, fence rows, etc. They can form large colonies in just a few years and their size allows them to invade natural habitats. If you find ferny plants in your yard, flower beds, or garden, check the stems to see if they are light green with maroon spots… This is not a plant you want or allow to spread! I can’t understand why such a deadly species is allowed to freely grow along public highways and backroads. It could be because not many people know what it is.

One of the most distinguishing features of Conium maculatum is the stems. They are round, hollow, hairless (glabrous),  and light green with maroon spots. The plants produce multiple branches.

Another feature is their pinnately compound leaves. The basal (lower) and lower stem leaves are 3-4 times compound, have long petioles (leaf stems), with somewhat inflated sheaths.

The upper stem leaves are similar, 2-3 times compound (with multiple leaflets), with short petioles or sessile (no petioles), and have longer sheaths. The leaves grow alternately along the stems with basal leaves up to 18” long and 12” across, the leaves becoming smaller as they ascend the stem.

The leaves are broadly ovate to triangular-ovate and taper to a blunt or sharply pointed tip. Yeah, I touched it because I wasn’t sure what it was at the time, but I was suspicious. I went into the house and washed my hands thoroughly. Once I knew what it was, I wore gloves when I photographed the plant behind the barn…

The tips of the branches terminate with multiple umbels of small white flowers. Each umbel has long peduncles (primary rays) connected to the stem that is surrounded by 4-8 involucral bracts. The compound umbels are 2-5” wide and contain 8-16 umbellets with 12-25 flowers. 

The above photo from the Missouri Plants on their Conium maculatum page is great and much better than I could take since I didn’t want to get too close… Missouri Plants provides many pages of great descriptions and photos. They also have a great glossary of plant terminology. Before I started using iNaturalist’s drag-and-drop feature, Missouri Plants was my number one source for wildflower identification. Now I use the site as a cross-reference to make sure iNaturalist is correct. Missouri Plants is from the Missouri Botanical Garden…

Each flower is about 1/8” across and consists of 5 white petals (one usually larger than the others), 5 white stamens that alternate with the petals, white filaments, and yellowish-white anthers.

On top of the ovary and base of the style is a flat-like stylopodium which some sites refer to as a “landing pad” for insects. 

The above two photos are from the Iowa Plants website on their Conium maculatum page. I couldn’t possibly get such good close-ups. Iowa Plants is a great website and many of the species pages have great close-ups that have helped me a lot.

Conium maculatum starts flowering in May and continues through August in my neck of the woods in west-central Missouri.

The fruit of Conium maculatum are referred to as schizocarps and the seeds are called mericarps.

Other members in the family are similar in appearance with different levels of toxicity. All parts of Conium maculatum are highly poisonous to humans and livestock and fatal. I would advise you NOT to handle this plant, especially without gloves. Even with gloves, it is advised to only handle it for a short period. Even the fumes from this plant are poisonous. If you have them on your property, spraying is the recommended method to kill them. If you pull them up, use protection, and do so only if you have a few plants. Once these plants flower and go to seed, they will die. However, even the dead plant’s stems remain poisonous for at least 3 years. It doesn’t take much of a dose to be fatal and there is no antidote…

Socrates killed himself with Poison Hemlock to avoid being executed. Likely, it would have been used to kill him anyway, but I guess he wanted to do it himself. Athenians (Greeks) used to execute prisoners and others with Poison Hemlock. 

There are a few more photos at the bottom of the page…

I have enjoyed photographing and learning about the many wildflowers growing on the farm and in other areas nearby. The farm I live on is in Windsor, Missouri in Pettis County (Henry County is across the street, and Benton and Johnson aren’t far away). I have grown over 500 different plants and identified over 250 species of wildflowers (most have pages listed on the right side of the page). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can vary from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
FLORA OF MISSOURI (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
USDA PLANTS DATABASE
DAVE’S GARDEN
MISSOURI PLANTS
MSU-MIDWEST WEEDS AND WILDFLOWERS
iNATURALIST
WILDFLOWER SEARCH
ILLINOIS WILDFLOWERS
MINNESOTA WILDFLOWERS
KANSAS WILDFLOWERS AND GRASSES
IOWA PLANTS
NORTH CAROLINA STATE UNIVERSITY
PFAF (PLANTS FOR A FUTURE)
GO BOTANY
MARYLAND BIODIVERSITY PROJECT
UNIVERSITY OF WASHINGTON/BURKE HERBARIUM
WILDFLOWERS OF NEW MEXICO
SEINet
SCIENCE DIRECT

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is the most reliable and up-to-date plant database and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂

MORE PHOTOS…