Water Hemlock is a native erect perennial semi-aquatic forb, growing from 2 to 7 feet in height on stout hollow stems which branch occasionally. The lower stem is usually the hollow part, with the upper more filled. Stems are smooth, streaked with brown and purple lines, with more pronounced color at the nodes.
The leaves are 2 to 3 times pinnately divided and alternate on the stem. Leaf divisions are paired plus a terminal division. Lower leaves can be over one foot long while the uppers are much shorter. Each individual leaflet is lance shaped, shiny green top and bottom, thin, with sharp coarse teeth, with leaf veins ending in the notches of the leaf margin rather than at the teeth. The leaflet margins tend to fold upward from the central vein, forming a wide "V" shape. Most leaf divisions will have 3 leaflets per division but the larger bottom leaves can have many more leaflets, particularly on the terminal division of the leaf. The stalk of the leaf forms a sheath around the stem.
The inflorescence is a compound umbel with many clusters on long stalks from the leaf axils. The umbel can have up to 20 umbellets with up to 20 flowers each, with the whole compound umbel spanning about 3 to 6 inches across. The stalks of the umbellets are of unequal length giving the entire cluster a semi flat-topped appearance.
Each flower is only 1/8 inch wide with 5 white petals that are notched at the rounded tip and very narrowed at the base. These and the sepals are attached to a yellow-green disc that is the upper part of a double ovary. There are 5 stamens with white filaments inserted on the disc and a divided style on the ovary. The stamens visually appear in-between the petals.
Seed: Fertile flowers produce an ovoid seed structure that separates into two 3-angled seeds that have a prominent oil tube on the seed wall. The separation side is flat, the rounded outer sides have dark and light brown stripes.
Toxic: This plant is highly poisonous. See text below.
Habitat: Water Hemlock grows from a thick, fleshy tuberous root system that is bunched in a cluster at the swollen base of the stem. It will be found in the moist soils of marsh edges, prairies and meadows. It can tolerate standing water for only short periods. It spreads by re-seeding.
Names: The genus, Cicuta, is an old Latin name for the poison hemlock. The species, maculata, is used to refer to spotted or mottled plants. The author name for the plant classification, 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
Comparisons: C. maculata differs from the other member of the Cicuta genus found in Minnesota, Bulblet Water Hemlock, C. bulbifera, by having leaves that are 3-times compound and are broader than C. bulbifera; by being much taller and by not having bulblets in the leaf axils. Otherwise, the flower umbels are similar. Two non-native plants that have similar flower umbels that can be compared are Fool's Parsley, Aethusa cynapium and Japanese Hedge Parsley, Torilis japonica.
Above: Water Hemlock is a tall plant. The inflorescence is a compound umbel with many clusters on long stalks from the upper leaf axils. Drawing courtesy USDA-NRCS Plants Database.
Below: Each small flower has 5 white petals, notched at the tip and very narrowed at the base. There are five stamens rising from a yellow-green central receptacle and placed in-between the petals.
Below: The ovoid seed structure separates into two 3-angled seeds that have a prominent oil tube on the seed wall. The separation side is flat, the rounded outer sides have dark and light brown stripes
Below: 1st photo (and photo above) - The inflorescence is a compound umbel with many clusters on long stalks from the leaf axils. The umbel can have up to 20 umbellets with up to 20 flowers each, with the whole compound umbel spanning about 3 to 6 inches across. 2nd photo - Leaves are 2 to 3 times pinnately divided and alternate on the stem. Most leaf divisions will have 3 leaflets but the larger bottom leaves can have many more leaflets, particularly the terminal division of the leaf. Most leaves are low on the stem. 3rd photo - Stems are smooth, streaked with brown and purple lines. The stalk of the leaf forms a sheath around the stem.
Below: The terminal division of the large lower leaves have more leaflets than the lower divisions, whereas the smaller upper leaves will usually have only 3 leaflets per division.
Below: This view of a leaflet underside shows the lateral veins ending at the leaflet margin in the notches of the teeth. Note also the slight upward folding of the margins into a shallow "V".
Notes: Water Hemlock is indigenous to the Garden. Eloise Butler noted it on Sept. 12, 1909. Martha Crone reported it in bloom on June 24, 1938 and it was still in the Garden at the time of her 1951 census. Water Hemlock is found throughout North America except Nunavut, Newfoundland and Labrador. There are several varieties recognized and within Minnesota the variety maculata is present and found throughout the state with exception of a few counties in the center of the state. The only other species of Cicuta in the state is Cicuta bulbifera, the Bulblet-water Hemlock.
Toxicity: The green stem and leaves are poisonous and the roots are much more so, concentrating a poison known as 'cicutoxin'. Browsing cattle and sheep can easily pull a root from the soil when browsing new green growth. A single section of root can kill a cow, hence the old name of Cowbane. Children are quite susceptible to the poison and ingestion causes cramps, vomiting and convulsions within 60 minutes, usually results in death in a very short time. At a minimum there is damage to the central nervous system of adults. The roots has a pleasant aromatic taste, which hides the toxin, and can thus be mistaken from turnips or artichokes. C. maculata is considered the most poisonous plant in North America.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"