African rue or Harmel [Peganum harmala L.][PEGHA][CDFA list: A] Photographs Map of Distribution

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SYNONYMS: harmel, Syrian rue, ruin weed, rue, wild rue

GENERAL DESCRIPTION: Bushy, herbaceous perennial with short creeping roots, to 0.8 m tall. African rue contains numerous alkaloids and all plant parts are toxic. Seed coats contain the alkaloid harmine and are especially toxic when ingested. However, livestock seldom consume plants because of the bitter taste. Toxicity symptoms in guinea pigs include weakness and paralysis of the hindquarters. Dehulled seeds yield edible oil similar to cottonseed oil. Plants have been used medicinally and produce red dye in the Middle East. Introduced from the Mediterranean region and Middle East.

SEEDLINGS: No description available.

MATURE PLANT: Stems stiff, erect, highly branched, angled above, glabrous. Leaves alternate, fleshy, bright green, 2-5 cm long, irregularly divided 3 times or more into linear segments. Stipules bristle-like.

ROOTS and UNDERGROUND STRUCTURES: Taproot branched, with stout, short-creeping lateral roots usually greater than 15 cm deep. New shoots can develop from lateral roots.

FLOWERS: Late spring-early fall. Flowers white, ~ 2.5 cm in diameter and solitary on stalks 2-5 cm long or more in the leaf axils. Sepals 5, linear, ~ 1.5 cm long. Petals 5, oblong, ~ 1.5 cm long.

FRUITS and SEEDS: Capsules spherical, leathery, 7-15 mm in diameter, orange-brown at maturity, 3-chambered, and opening by 3 valves at the apex to release numerous dark brown to black angular seeds, 3-4 mm long.

POSTSENESCENCE CHARACTERISTICS: Above ground parts die back in winter.

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HABITAT: Dry places, such as roadsides and abandoned fields, in desert and semi-desert regions. Grows best on sites that receive some run-off water.

DISTRIBUTION: Uncommon. Mojave Desert (cw San Bernardino, se Kern cos.).

PROPAGATION/PHENOLOGY: Reproduces primarily by seed, but roots can produce new shoots, especially when severed. Most seed falls near the parent plant, but some seed dispersed by water, human activities and machinery, or by adhering to the feet, fur, or feathers of animals. Seeds can germinate under fairly saline conditions. Germination starts in early spring and is sporadic throughout the growing season when adequate moisture is available. Seedlings emerge from soil depths to 3 cm, but most emergence occurs from the upper 0.5 cm.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Cultivation can severe roots and encourage growth of new shoots.

SIMILAR SPECIES: African rue is the only species in the genus Peganum occurring in California and is unlikely to be confused with any other plants.

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Prevention and control: African rue and Syrian bean-caper are both noxious perennial weeds in the caltrop family and are native to the Mediterranean and central and southwest Asia. Syrian bean-caper was believed to have been introduced to California in 1931 as a contaminant in alfalfa seed from Turkestan. African rue was introduced to the United States in 1931. These weeds are primarily problems in degraded rangeland habitats or waste areas along roadsides. Both exhibit a bushy appearance and die back to the crown each winter. New shoots arise from the crown or lateral roots and extend in a radial fashion from the main taproot. Both species are generally unpalatable to livestock and African rue has been reported to be highly toxic to cattle, sheep, and horses.
Mechanical removal is a difficult task for either species. The strong, deep taproot and lateral roots must be removed for control. Plants may be cut back to the crown, but regrowth will occur. Tillage will only serve to spread infestations by severing and dragging rootstocks to new areas. Longevity in the seed bank for both species is unknown.
Grazing is not an effective control option, due to non-palatability or toxic effects. There are also no available biocontrol agents for either species.
The most effective control strategy is a dilute spot application of glyphosate to the foliage of actively growing plants in the bud stage. It will be necessary to repeat this, possibly several times until the plants are completely killed. Other nonselective herbicides such as tebuthiuron, diuron, and bromacil have provided good roadside control. Triclopyr, 2,4-D, and dicamba may also be effective, but no evidence has been reported in the literature. Refer to the herbicide labels for rates and precautions.

Parsons, W. T. and Cuthbertson, E. G. 1992. Noxious weeds of Australia. Melbourne, Inkata Press.
Roche, C. T. 1991. Syrian bean-caper. Pacific Northwest Extension Bulletin 370.
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