African Rue
Peganum harmala
Class B
Llimited to portions of the state. In areas with severe infestations, management should be designed to contain the infestation and stop any further spread.
Children & Pets
This plant may pose a particular risk to unsupervised children and animals due to its toxicity or potential for injury.
Toxic to Horses
This plant has been documented to sicken or injure horses.
Livestock Hazard
This plant presents a threat to the health and/or quality of livestock.
Warning! If you may have ingested or inhaled this plant, contact poison control immediately at 1-800-222-1222
QUICK FACTS
- African Rue is a small, green succulent perennial that grows like a bush. It grows 1-2 feet in height and about 3 feet in diameter. It has smooth, bright green leaves and stems and small white flowers.
- It grows in dry, disturbed areas, especially grasslands, roadsides, and rangelands. Its ability to spread by seed and vegetatively has allowed it to take over in many areas of the southwest. This weed is extremely drought-tolerant and grows in alkaline and saline soils.
- African rue, native to the Mediterranean region and parts of North Africa, was intentionally planted in New Mexico to make red dyes. However, this weed is highly toxic to animals and humans and should never be eaten. Symptoms include trembling, incoordination, and hemorrhaging in the heart and liver.
1. Overview
An extremely poisonous weed in many western states.
African rue was introduced to New Mexico in 1928 by a farmer trying to make red dyes. It quickly became invasive in the area and took over disturbed fields, roadsides, and grazing areas. This weed spreads both by seed and root fragments, grows deep roots, and produces allelopathic chemicals, making it difficult for other vegetation to establish in infected areas. African rue is also extremely poisonous to humans and animals. [3,4]
History of Poison Hemlock
Native to the Mediterranean and North Africa, African rue was used to create red dye and some medicinal compounds. It was first introduced to the U.S. intentionally by a farmer trying to grow red dye near Deming, New Mexico, in 1928. It quickly spread to other western states and continues to infect many areas in New Mexico. [3,4]
Currently, it is listed as a noxious weed in New Mexico, Arizona, California, Colorado, Nevada, and Oregon. It continues to cause injury to livestock that graze in infected fields. While it mainly invades dry, disturbed areas, it easily outcompetes other plants and produces allelopathic chemicals that prevent further growth. [4]
2. ID Guide
What does it look like?
African rue is a bush-like succulent. It grows to 1-2 feet tall and 3 feet wide, with bright green leaves and stems. The leaves and stems are smooth and hairless. In the spring and summer, it grows small white flowers with five petals on leaf axils. Flowers can grow a green fruit that produces many seeds. This plant was named after its resemblance to rue, but has different leaves (bright green and linear), and the flowers are white instead of yellow. [2,3]
Having trouble identifying a weed? Contact your local conservation district or county extension agent.
Key Features
- Plant: African rue has multiple branches and looks like a bush. It has bright green stems and leaves that are smooth and fleshy. This weed grows up to 2 feet tall and 3 feet wide. Plant flowers in spring with small, white, five-petaled flowers and a cylindrical green fruit. This plant dies back in the summer when it’s hot and grows again in the fall when more moisture is available. [2,3]
- Roots: African rue has a deep, extensive root system consisting of one taproot and shorter, creeping roots. The taproots are woody and can grow up to 25ft deep to follow water. Creeping roots can extend up to 20 feet away from the parent plant and usually grow about 15 inches below the surface. [3,8]
- Leaves: The leaves are bright green, smooth, and alternate along the stems. They are flat and deeply lobed, with very thin linear leaflets. When crushed, leaves have a disagreeable odor that usually deters livestock. [1,8]
- Flowers: African Rue flowers have five white petals with green sepals that wrap around the flower, and yellow stamens inside. They are usually present during late spring to fall and are located on the axils of the leaves. [1,4]
- Seeds: Seeds grow inside a fruit, which can be green, orange, or brown, and grow from the flower. The seeds are about 4mm long, red or blackish-red, have a rough surface, and are somewhat triangular, like an orange wedge. African rue plants can produce thousands of seeds per plant, with approximately 1,000 fruits per plant and 50 seeds per fruit. [4,5,7]
John Cardina, The Ohio State University, Bugwood.org
Flowers grow in a half-dome of small umbrella-like clusters at the ends of branched stems.
Ohio State Weed Lab , The Ohio State University, Bugwood.org
Poison hemlock will appear shorter and more carrot-like in its first year of growth.
Ansel Oommen, Bugwood.org
The long taproot resembles a white carrot, characterized by its thick base and typically white color.
Ansel Oommen, Bugwood.org
Leaves have a fern-like appearance and are finely pinnately divided.
Jan Samanek, Phytosanitary Administration, Bugwood.org
The plant itself can grow 6ft-10ft tall, and the stems are usually ribbed, hollow, and have purple splotches/streaks.
Ken Chamberlain, The Ohio State University, Bugwood.org
Green, round, and deeply ridged fruits develop from each tiny flower. Each fruit contains several small seeds, which are flat with ridges.
3. Infestation Basics
“A man fond of growing unusual plants had obtained Peganum harmala seed from Europe. The plant grew well, and spread after cultivation had ceased, and could not be eradicated.”
– V.L. Cory, 1949
Where and how does it grow, and how does it spread?
This weed has adapted to various environments, but prefers dry, disturbed areas such as roadsides, grasslands, and fields. It can spread by both seed and root fragments that can be carried in equipment like vehicles and mowers. [4]
African rue can grow in several different locations, but prefers dry areas where the soil has been recently disturbed. They are not flood-tolerant and often drown in excessive water, but they will establish in areas with sufficient moisture availability as well. They are extremely drought-tolerant, and usually grow faster than the vegetation around them, allowing it to take over. [8]
It is an herbaceous perennial that grows primarily from fall to spring, then dies back in the summer and winter to take advantage of the dry seasons. In New Mexico, plant foliage dies back and survives through its roots in winter, then begins its annual growth in March. After flowering in late spring, the plant typically dries and develops a woody base in summer, allowing it to concentrate on fruit growth. Flowers persist generally from April to September. African rue then grows a second vegetative cover that lasts until freeze in early November. [8]
African rue spreads by means of rhizomes, root fragments, and seeds. Although seed longevity is unknown, it is theorized to be several years. Each plant can produce up to 50,000 seeds that can be spread by equipment, animal, or human movement, and water. Rhizomes typically grow 15 feet underground and can extend up to 20 feet away from the parent plant, providing this plant with a significant opportunity to invade new areas. Additionally, this weed can regrow from root fragments created when attempting to remove it, creating more plants than before. [6,8]
Key takeaway: African rue can grow from seeds, rhizomes, and roots in any area with disturbed soil, especially in dry areas. It is spread easily through equipment, water, and human or animal movement.
Why is it so invasive?
African Rue is highly toxic to all animals and humans. It is a fast-growing plant that can be produced from seed, rhizome, or root fragments, and is allelopathic, providing it with several opportunities to take over wherever it is introduced. [4]
This weed has adapted to grow in very dry areas by taking advantage of moisture in the fall and spring before other plants have the opportunity to grow. This plant grows extremely fast and releases allelopathic chemicals into the soil that prevent other plants from establishing nearby. Additionally, this plant has an extensive root system that takes vital resources (like water) from other plants. [4,8]
African rue can spread by seed, rhizome, and root fragments, providing multiple opportunities for its spread. It produces thousands of seeds per plant that equipment, water, animals, or human movement can carry. Root fragments can spread similarly after soil is disturbed, and plants can regrow from fragments as small as an inch. Additionally, this plant can extend its creeping roots up to 20 feet away from the parent plant. [8]
African rue is also toxic to humans and animals if eaten. Although most animals avoid this plant because of its odor, hungry grazers may eat this plant and die shortly afterwards. Consuming as little as 0.15% of the animal’s body weight can lead to serious health issues. [3,4]
Key takeaway: This weed can grow in various locations, spread by root, seed, and rhizome over very long distances, and outcompete other vegetation. African rue is also extremely toxic and can be fatal to anything that eats it.
Common risk factors for invasion
- Disturbed Soils: African rue loves to invade areas where soil has been disturbed, such as construction sites, tilled fields, or overgrazed pastures. This disruption weakens existing vegetation and allows the weed to become established. Minimizing unnecessary soil disturbance can help reduce the risk of invasion.
- Moisture availability: While African rue has adapted to a wide range of soil and water conditions, it spreads more easily in areas with adequate moisture, making irrigated lands and riparian areas vulnerable to infection. Permanent waterlogging will kill the plant, so infestations are more pernicious on sites with well-draining soil.
- Site dryness: African rue spreads much more easily on drought-prone, rocky, or sandy sites, and often outcompetes other vegetation in areas with limited water.
- Desert Environments: African rue will not survive in frequently flooded areas or regions with heavy rainfall. The plant prefers dry, hot environments.
Impacts
Ecosystem Health
Once established, African rue displaces native plants, resulting in a notable loss of floral and faunal biodiversity. This can significantly reduce forage availability for game, particularly during the winter months, and may even alter migratory patterns. African rue grows its roots aggressively and competes with other vegetation for limited resources like water. Additionally, African rue is allelopathic, which further prevents other plants from growing in infected areas. This, in turn, reduces the amount of forage plants that are available for wildlife and livestock. [4,8]
Health and Safety
African rue is highly toxic and can cause death when consumed. As little as 0.15% of a person or animal’s body weight can cause detrimental effects. It can lead to hemorrhaging of the heart, loss of appetite, trembling, loss of coordination, and abortion. [4]
Livestock
Sheep, goats, cattle, and horses are known to graze on various types of weeds, often utilizing specific species as a food source. However, African rue is an exception, as it is highly toxic and unpalatable to all living creatures. When livestock consume this plant, it can lead to hemorrageing, ultimately resulting in death. [3,4]
In pregnant livestock, ingestion of this toxic plant not only poses a lethal risk but may also endanger the developing fetus. [3,4]
4. Management Strategies
Prevention is the best method of managing this weed, as it is very difficult to manage once it is introduced to an area. African rue mainly invades disturbed areas, so keeping the soil undisturbed and covered in desired vegetation often keeps plants away. Prevent seed dispersal by cleaning equipment. If infection occurs, the best way to remove this weed is a combination of mechanical and chemical methods. The depth of the roots makes it nearly impossible to eradicate by pulling or digging, but this may prevent seed dispersal, especially when removing seedlings or young plants. Mowing and plowing are not recommended as they often spread roots and allow for plants to regrow. Because of how toxic this weed is, it is important not to let any animal graze on it. Herbicides can be effective at killing roots. [8]
DO’s
- Maintain healthy vegetation cover and avoid disturbing the soil, as this provides plants with the opportunity to grow.
- Prevent animals from grazing in areas where this plant is infected, as it is highly toxic.
- Clean equipment after use to prevent the spread of seeds or roots to new areas.
DON’Ts
- Mow or plow infected areas, as this often spreads roots and allows for more growth.
- Allow it to become widespread, as this plant is easier to deal with when young, individual, or small infestations.
- Travel through infected areas with animals or vehicles, as they often spread seeds.
** The following information is provided courtesy of the UC Weed Research and Information Center. The Taos Soil and Water Conservation District does not endorse the use of any particular product, brand, or application thereof. **
Most non-chemical control is ineffective, with the exception of hand-pulling.
| Hand-pulling | When hand-pulling, the roots must be removed or the plant will re-sprout. |
DiTomaso, J.M., G.B. Kyser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, University of California. 544 pp.
5. Citations
[1] USDA. (2018). Poison Hemlock (Conium maculatum): USDA ARS. Usda.gov. https://www.ars.usda.gov/pacific-west-area/logan-ut/poisonous-plant-research/docs/poison-hemlock-conium-maculatum/
[2] CAL-IPC. (2017, October 16). Poison Hemlock (Conium maculatum). California Invasive Plant Council. https://www.cal-ipc.org/resources/library/publications/ipcw/report32/
[3] CSU. (2024). Guide to Poisonous Plants – College of Veterinary Medicine and Biomedical Sciences – Colorado State University. Colostate.edu. https://poisonousplants.cvmbs.colostate.edu/plant/100
[4] Anderson, E., Branstrom, I., & Hill, E. (2023, April 20). Poison hemlock identification and control. Www.canr.msu.edu. https://www.canr.msu.edu/news/poison-hemlock-identification-and-control
[5] Minnesota Department of Agriculture. (n.d.). Poison Hemlock. Www.mda.state.mn.us. Retrieved August 5, 2025, from https://www.mda.state.mn.us/plants/pestmanagement/weedcontrol/targetplants/elimtargetplants/poisonhemlock
[6] King County W.A. (2024). Poison hemlock identification and control. Kingcounty.gov. https://kingcounty.gov/en/dept/dnrp/nature-recreation/environment-ecology-conservation/noxious-weeds/identification-control/poison-hemlock
[7] Cleveland Clinic. (2022, September 8). Hemlock Poisoning: Symptoms, Treatment & Prevention. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/24122-poison-hemlock
[8] Plato. (1996). Phaedo. Cambridge University Press. (Original work published 4th century B.C.E.)
[9] Levy, J. (2011). Poison. Lyons Press.
[10] Sheley, R. L., & Petroff, J. K. (1999). Biology and Management of Noxious Rangeland Weeds. Oregon State University Press.
Chris Evans, University of Illinois, Bugwood.org
Symptoms of Hemlock Poisoning
- Sweating
- Vomiting
- Dilated pupils
- Excess salivation
- Dry mouth
- Rapid heartbeat
- High blood pressure
- Restlessness or confusion
- Muscle weakness and muscle twitches
- Tremors and seizures
Late Stage:
- Slow heartbeat
- Low blood pressure
- Muscle paralysis
- Muscle breakdown and muscle death
- Kidney failure
- Central nervous system depression
[7]