Montana Field Guide

PLANTS: A taprooted, perennial forb with erect, usually branched stems, 40-100 cm tall. Sometimes, matt-forming. Plants are aromatic and covered with dense, fine, gray-white hairs (canescent). Sources: Schultz in Flora of North America (FNA) 2006; Lesica et al. 2022

LEAVES: Gray-green and arranged as a basal rosette or alternately on the stem. Leaf stems (petioles) are present. Blades are ovate in outline, 2-3 times pinnately divided into linear-lanceolate segments, and 2-10 cm long. Leaves are reduced and less divided upwards. Sources: Schultz in FNA 2006; Lesica et al. 2022

INFLORESCENCE: An open, diffuse, and leafy panicle of greenish-yellow flower heads that droop. Flowers are arranged in small, roundish heads. Flower heads consist of disc florets (discoid) and subtended by green, tomentose involucral bracts, 2-3 mm long. The central florets have both stamens and pistils (perfect) while the marginal florets have only pistils. Pappus is absent. Receptacle has long, soft, crooked, and unmatted hairs (villous). Sources: Schultz in FNA 2006; Lesica et al. 2022

Absinth Wormwood flowers from mid-summer to fall (Schultz in FNA 2006).

Montana has about 19 Artemisia species, generally referred to as sagebrush, sagewort, mugwort, and wormwood. Of these 8 species are well-developed shrubs, and the remainder are woody at their base (sub-shrubs) or herbaceous. A technical field guide should be used to identify Artemisia species.

Artemisia species that have flowerheads with hairy receptacles, marginal pistillate florets, and perfect central florets:

Absinth Wormwood - Artemisia absinthium, non-native, invasive, undesirable
* Plants: Robust, herbaceous, perennial forb. Aromatic. Hairs dense, fine, gray-white hairs (canescent).
* Root: Taproot.
* Leaves: Gray-greenish, and ovate in outline. Pinnately divided 2-3 times into linear-lanceolate segments, at least 2 mm wide.

Fringed Sage - Artemisia frigida, native
* Plants: Short, perennial sub-shrub. Aromatic. Hairs canescent to dense, soft, andinterwoven hairs (tomentose).
* Root: Branched caudex.
* Leaves: Gray-greenish, and oblong. Divided 2-3 times into linear segments, about 1 mm wide.

Alpine Sagebrush - Artemisia scopulorum, native
* Plants: Smaller, herbaceous, perennial forb. Hairs stiff, straight, sharp, and appressed (strigose) to canescent.
* Root: Branched caudex.
* Leaves: Gray-greenish, and ovate in outline. Divided 2 times into linear-oblanceolate segments, about 1 mm wide.

Some of the Artemisia species that have flowerheads without hairy receptacles and with marginal pistillite and central perfect florets:

Biennial Wormwood - Artemisia biennis, native
* Plants: Annual or biennial, herbaceous forb. Little to not odorous. Hairs lacking (glabrous).
* Root: Taproot.
* Leaves: Greenish, and oblanceolate in outline. Divided into dentate, lanceolate segments and coarsely toothed

White Sagebrush - Artemisia ludoviciana, native, desirable
* Plants: Perennial, herbaceous forb. Aromatic. Hairs short and soft (pubescent).
* Root: Rhizomatous.
* Leaves: Gray-greenish, linear lanceolate, with entire, lobed, or deeply-lobed margins - depending upon the subspecies which intergrade.

Common Wormwood - Artemisia vulgaris, non-native, occasionally escapes cultivation
* Plants: Perennial, herbaceous forb. Faintly to not aromatic. Hairs absent to sparse.
* Root: Rhizomatous.
* Leaves: Uniformly green or bicolored (green upper side and whitish lower side, lanceolate, ovate, or linear, with deep-pinnately divided lobes. Main stem leaves with 1-2 pairs of lobes on the petiole!

Absinthe is the name of an alcoholic drink, made with Artemisia absinthium, that was popular in the 19th-20th centuries, but eventually banned due to its cumulative toxic properties (Arnold 1989).

Pliny (Gaius Plinius Secundus), a Roman author of Historia naturalis, naturalist, and natural philosopher described the plant has having a long-established use against gastrointestinal worms, thus the name "wormwood" (Arnold 1989). Wormwood in French is absinthe and in German is <Wermut (Arnold 1989).

The genus name, Artemisia comes from the Greek word Artemis who is the goddess of the hunt, wilderness, and vegetation (Schultz in FNA 2006).

Absinth Wormwood grows along roadsides and streams (riparian areas) and in fields and talus slopes within the plains and valleys zones of Montana (Lesica et al. 2022). Where planted plants will persist (Shultz in FNA 2006). Plants often establish where there is some disturbance, either from natural or anthropogenic sources, and little competition from other plants (Evans 1982).

CULTURAL USES
From ancient Egypt to the 21st Century, the cultural uses of Absinth Wormwood has a rich history. The plant has been cultivated since at least the Middle Ages. Readers who want to learn more should consult "useful links" in this section and the fascinating Absinthe article by Wilfred Arnold (1989).

Wormwood [Adapted from Arnold 1989]
The oldest recorded use of Absinth Wormwood is found in the ancient Egyptian medical text, dating to around 1550 BCE. For Egyptians, this plant had religious and medical significance.

In the First Century AD, Pliny, the Roman author of Historia Naturalis recorded how extracts of Absinth Wormwood were used against gastrointestinal worms, and to fortify a wine known as 'absinthites'. Most species of Artemisia, including Artemisia absinthium, contain a ketone and monoterpene (Wikipedia 2026) called thujone. Thujone has been found to stun roundworms, which are then expelled by the normal peristaltic action of the intestine. Thujone is also known to cause hallucinations, convulsions, and permanent damage to the nervous system.

Additional applications of Absinth Wormwood were described by Pedanius Dioscorides, a Greek physician, who authored the De Materia Medica from 50 to 70 CE. This five-volume work became the authority on medicines and medicinal plants for the next 1,500 years (Wikipedia 2026). The plant's juices were used to anoint arms and legs to repel gnats and fleas, and also attached to stored garments to keep out the moths.

Absinthe [Adapted from Arnold 1989; Wikipedia 2026]
With the advent of steam distillation in the 16th century, the process to distill fermented cereals into grain alcohol led to the invention of liqueurs. By the late 1700s, the formulation of Absinthe was created in Switzerland. From the 1800s to very early 1900s, Absinthe became a very popular drink in France, Switzerland. and extending into America. To the standard ingredients of alcohol and Absinth Wormwood oil, the extracts of anise, fennel, hyssop, and melissa (lemon balm) were added along with lesser amounts of angelica, dittany of Crete, juniper, nutmeg, star anise, and veronica. As the drink became more popular, many variations were created, sold, and drunk.

What absinthe had to offer was an intoxicating drink with a colorful appeal, but a naturally bitter taste. From the wormwood, came the constituents of thujone, a dangerously additive psychoactive drug, that causes hallucinations, absinthin, which is probably the second most known bitter substance, and chlorophyll which made it green. To overcome its bitterness, the bright green absinthe was poured into a glass. Upon the glass a sugar cube atop a silver sieve was placed. Cold water was slowly poured over the cube, which turned the liqueur to opalescent yellow. It is the appearance, taste, and effect of the drink that made is popular into 1913.

People from all walks of life consumed absinthe. It was popular with soldiers and their compatriots. Many famous artists, poets, and writers not only drank absinthe, but added it to their paintings and stories. These included among man others, Vincent van Gogh, Pablo Picasso, Ernest Hemmingway, and Lewis Carroll.

The intoxicative appeal came not from the very high ethanol content, but primarily from thujone, with contributions from potentially other questionable ingredients. Since 1859, studies on absinthe demonstrated its ability to create convulsions, involuntary evacuations, abnormal respiration, and foaming at the mouth in animals. Additional studies observed absinthe to cause visual and auditory hallucinations in human beings. Excessive consumption of absinthe could cause the disease Absinthism which has the symptoms of addiction, hyper-excitability, hallucinations, brain damage, sleeplessness, tremors, and convulsions.

Despite the scientific warnings, association with violent crimes and social disorder, and efforts by the French government to ban the drink, the absinthe drinkers and the people profiting from its sale denied such claims. In 1900, the chemical structure of thujone was published by Friedrich Semmler, a German chemist. By 1916 European and American scientists documented the permanent damage that it causes to the neurological system. Between 1906 and 1914, Brazil, Belgium, Netherlands, Switzerland, US, and France banned absinthe. However, in the 21st century new types of absinthe have emerged.

Treatment for Malaria [Adapted from Arnold 1989; Wikipedia 2026]
Artemisinin, also known as qinghaosu, is a potent medication used to treat malaria. Since the 1st century, extracts of qinghaosu from many plant species, including Absinth Wormwood have been used. In the 19th century when malaria was common in the Mediterranean region, French soldiers added to their wine an extract from Absinth Wormwood, in hopes of preventing malaria. Unfortunately, the potency of ginghaosu in Absinth Wormwood is not enough to be effective.

Useful Links:
Herbal Reality
Henriette's Herbal Homepage

ALLELOPATHY
Allelopathy is a biological phenomenon that allows a plant species to exude at least one biochemical that can influence (negatively or positively) the germination, growth, and/or survival of neighboring plants (Wikipedia 2026). Absinth Wormwood is considered to be alleopathic (Carey1994). Plants contain absinthin which can be toxic to other neighboring plants.

A study found volatile biochemicals emitted from the leaves prevented germination in wheat (Triticum triticale; inhibited seedling growth in wheat, Whitetop (Lepidium draba, and Common Flax (Linum usitatissimum; and greatly stimulated seedling growth in White Mustard (Sinapis alba) (Evans 1982; Carey 1994). Extracts made from the leaves was shown to prevent germination for the 4 previously mentioned species. Extracts made from roots prevented germination for wheat and reduce root and stem elongation for Whitetop, Common Flax, and White Mustard.

Another study found Absinth Wormwood inhibited the germination of Needle-and-Thread Grass (Hesperostipa comata), but stimulated Green Needlegrass (Stipa viridula) (Carey 1994).

Absinth Wormwood reproduces by seed.

FLOWERS
Disk florets: Are either pistillate (female), 9-20 per head or bisexual (perfect; stamens and pistil), 30-50 per head. Corolla (petals), glandular, 1-1.5(2.0) mm long.

FRUITS
Fruit is an achene (or cypselae): more-or-less cylindric, slightly curved, obscurely nerved, glabrous, sometimes shiny, and less than 1 mm long.

GENETICS
Chromosome number of 2n=18 (Shultz in FNA 2006).

LIFE CYCLE [Adapted from Evans 1982 and Carey 1994]
Plant growth can begin in late April. Seedlings can emerge from late-spring to early-fall when soil moisture is adequate. Seedlings may be hard to detect as the plant leaves can be close to the ground before stems grow upright. Flower stalks are produced by mid-July. Seeds can remain viable for 3 to 4 years, even in undisturbed prairie soils. Seeds are dispersed by running water, wind, animals, farm equipment, and as a contaminant in hay. Rosettes can form by the end of the 1st growing season. Some researchers have suggested that plants can regenerate from fragmented lateral roots when plowed, but this is not supported by studies.

Absinth Wormwood is a non-native plant that often establishes in disturbed areas where there is little competition from other plants.

COUNTY & STATE DESIGNATIONS
As of 2024, Absinth Wormwood is listed as County Noxious in 5 counties of Montana: Beaverhead, Carbon, Flathead, Lincoln, and Meagher.

INTEGRATED VEGETATION MANAGEMENT
Successful management of non-native thistles requires that land-use objectives and a desired plant community be identified (Shelly et al. in Sheley and Petroff 1999). Once identified, an integrated weed management strategy that promotes a weed-resistant plant community and serves other land-use objectives, such as for livestock forage, wildlife habitat, or recreation, can be developed. Often a combination of compatible control efforts will better achieve the desired objectives.

PREVENTION
* Learn how to differentiate “native” from “non-native” species of Artemisia.
* Implement control methods, especially physical methods, prior to seed development.
* Prevent vehicles from driving through, and animals from grazing within, infested areas.
* Thoroughly wash the undercarriage of vehicles and wheels in a designated area before moving to an un-infested area.
* Frequently monitor for new plants, and when found implement effective control methods (Early-Detection and Rapid-Response).
* Maintain proper grazing management that creates resilience to noxious and non-native weed invasion.

PHYSICAL and CULTURAL CONTROLS

Tilling or plowing (fallow) in summer followed by a fall tillage can eliminate seedling (Evans 1982). Railing, chaining, roto-beating, discing, or plowing can be effective but must be timed appropriately – before seed set (Evans 1982).

Mowing can reduce, but not eliminate seed production because flowering can occur on stems close to the ground (Evans 1982). Repeated mowing, two to three times per season, is needed to weaken plants. Plants are difficult to mow because of their thick stems and establishment along fences, rocky places, etc.

FIRE
Absinth Wormwood may be killed by fire depending upon fire several and duration (Carey 1994). Plants have perennating buds at and near the soil surface. Low-severity fires can easily top-kill plants. After fire, regeneration is believed to occur from buds that are not killed by the fire. In South Dakota, almost two-thirds of the Absinth Wormwood population survived a fire with 2,000 to2,400 kilograms per hectare of dormant fine fuels. They were top-killed, but re-sprouted after the fire. However, after four consecutive years of annual spring burning, the Absinth Wormwood population was reduced by 96%.

Plants are a primary colonizer of disturbed ground, so revegetation efforts must be carefully planned and/or timed with responses to wild fire and burn prescriptions (Evans 1982; Carey 1994).

VEGETATION CONTROL
Desirable grasses that create vigorous competition can help control Absinth Wormwood (Carey 1994).

CHEMICAL CONTROLS
Chemicals are most effective when carefully planned, timed, and incorporated with long-term control tactics that include replacing weeds with desirable plant species, modifying land use management, and preventing new infestations. The herbicide type and concentration, application time and method, environmental constraints, land use practices, local regulations, and other factors will determine its effectiveness and impact to non-target species. Strict adherence to application requirements defined on the herbicide label will reduce risks to human and environmental health. Consult your County Extension Agent and/or Weed District for information on herbicidal control. Chemical information is also available at Greenbook.Clopyralid, dicamba, MCPA, picloram, 2,3-D, metsulfuron, and chlorsulfuron chemicals will all kill Bull Thistle plants. It is also critical that herbicides be applied to prevent damage to broadleaf and grass forage species and other non-target plants. Readers can also consult the references in Zouhar (2002).

Absinth Wormwood can be controlled with 2,4-D, Picloram, Dicamba, an glyphosate (Evans 1982; Carey 1994). Spraying in spring and fall may help reduce the application rate necessary for a 100% topkill. A second year of spraying may be necessary.

GRAZING CONTROLS
Livestock grazing does not directly control Absinth Wormwood. Absinth Wormwood is rated as unpalatable to fairly palatable for cattle, poor for horses, and good for sheep with energy and nutritional value listed as fair (Carey 1994). Livestock typically avoid eating Absinth Wormwood, especially after early spring. As a result, plants are not selected for by livestock, and can actually increase as grazing pressures on the land increase (Evans 1982).

BIOLOGICAL CONTROL
As of 2025, biological control agents are not available.

In Canada, the Pyralid Moth (Euzophera cinerosella) was studied as a potential biological control agent for Absinth Wormwood by Schroeder (1979). The larvae selected for, fed, and developed the best on Absinth Wormwood plants. However, recovered adults were found on several native sagebrushes, including Artemisia cana, Artemisia longifolia, and Artemisia dracunculus. This suggested that an introduction of this moth to North America could potentially cause problems for native sagebrush species.

Useful Links:
Central and Eastern Montana Invasive Species Team
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides

Absinth Wormwood is a non-native plant that can spread rapidly, and outcompete desirable plants in native grasslands, pastures, and fields (Evans 1982). Cattle generally do not eat Absinth Wormwood, and typically avoid it to graze on native and desirable non-native grasses and other forbs. As grazing pressures on the land increase, Absinth Wormwood populations often increase.

The presence of Absinth Wormwood in food products from animals or during harvesting can reduce yields and pose health risks for people (Evans 1982). Where dairy cows do eat Absinth Wormwood, the milk can take on a strong flavor and be rejected from processing. Likewise, wheat and other grain fields that contain the plant is considered tainted and rejected for use in flour. In harvesting fields, plant dust from Absinth Wormwood can cause allergic reactions or other problems.