Plants annual herbs, (10-)30-120+ cm tall. Leaf blades ovate to elliptic, 3-18+ cm long, 1-5(9+) cm wide, 1(-2) pinnately lobed, the ultimate lobes lanceolate to linear, 3-50 mm long and 2-15 mm wide, blade surfaces slightly to strongly scabridulous and gland-dotted, occasionally with erect hairs 1-2 mm long. Capitula borne in open panicles on peduncles 1-8(-15) mm long, obscurely radiate; outer phyllaries 5(-6), lance-elliptic, 2-4 mm long; inner phyllaries 5(-6) ovate to orbiculate, 2-5-4 mm long; ray florets 5(-6), pistillate, the lamina orbiculate to oblong, 0.3-1 mm long; disk florets 12-30(-60). Achenes obovoid, 1.5-2(-3.5) mm long, with pappus-like triangular to ovate outgrowths 0.5-1 mm long at the top. 2n = 34.
Parthenium hysterophorus is native to Mexico and the southeastern United States. It is now a widespread weed in tropical, subtropical and warm temperate regions. It is allelopathic, taints milk and meat, and sometimes causes serious contact dermatitis.
Although not included in the Flora of Somalia, Parthenium hysterophorus is a serious, widespread weed in Somaliland, growing in cultivated and urbanized areas. Its distribution in Somalia is not known but is probably similar.
Text modified from the account in Flora of North America.
Gu’yaal jire dhaqso u baxa, oo illaa 1.5 m ah. Wuxu leeyahay ur xooggan oo cayayaanku ka didaan. Caleemo isasoo eegaya, oo cagaar khafiifa ah, iyo xaad jilicsan oo aad u kala tagsan. Ubax yar oo cad oo leh shan geesood oo qaab kala durugsan ugu kala yaalla baasha sare ama dhinacyada. Midho madaw oo Afar ama Shan ah, iyo iniinyo isku ceshen oo ubax kasta ku yaal.
Sabo: Dhul cagta lagu badiyey iyo dhul daaqsimeed, joog ah 500 – 1500 m.
Filiqsanaanta: Harame ka baxa kulaale-xigeenka, asal ahaan Badhtamaha iyo Koonfurta Maraykanka.
Fiiro gaar ah: Geedkan waxa ku sumooba xoolaha iyo dadka. Geedku wuxu sii daayaa kiimikooyin xanniba koritaanka dhirta kale, waxa kale oo uu leeyahay xidid-udub oo hoos u qoto dheer oo ay adag tahay in la fujiyo.
Patel (2011) listed several studies in which Parthenium hysterophorus was found to have beneficial effects, but its negative impact on food security and health makes it a highly undesirable solution outside a very controlled situation. Remember, average seed production is 15,000 per plant, 20,000 seeds is common, 100,000 has supposedly been counted (I have not tracked down the source of the number).
Parthenium hysterophus is an aggressive weed of crops and waste places. It reduces crop and forage production, with severe infections resulting in losses of up to 90% (Naderi et al. 2024). It also taints meat and milk when grazed and can cause severe dermatitis after repeated contact.
Parthenium hysterophus spreads by seed, with individual plants producing an average of 15,000 seeds but vigorous plants produce many more, with as many as 100,000 being the highest number estimated. The seeds also have a high viability and can remain dormant in the soil for 8-10 years.
Control: Plants should be removed before flowering. One resource suggested focussing first on areas with the fewest plants and then spreading to more severely infected areas.
The seeds germinate when near the surface and require exposure to light. Some sources suggested deep plowing so as to bury the seeds. and covering a cleared area to reduce germination.
If plants are established, hoeing will not be sufficient to control them because the buried part of the root will resprout.
WARNING: Clean shoes and equipment used when removing Parthenium. The seeds are small and easily carried from one place to another.
Plants of the World Online (POWO): Parthenium hysterophorus. The distribution map shows the countries where the taxon is considered native or introduced but is now growing in the wild.
Global Biodiversity Information Facility (GBIF): Parthenium hysterophorus. Records may be of cultivated specimens.