Famine Weed
Parthenium hysterophorus
NEMBA: Category 1b
English: Famine Weed, Congress Grass, Carrot Grass, White Top, False Ragweed, Gajar Ghas
Afrikaans: Parthenium, Kongresgras, Wortelgras
Parthenium hysterophorus, commonly known as Famine Weed is a tall, highly branched annual plant with distinctive pale green, deeply divided leaves that look a bit like feathery carrot leaves. It's covered in masses of tiny, creamy-white, daisy-like flower heads, especially towards the top.
This plant is a notorious invader in South Africa, not just because it spreads incredibly fast and takes over disturbed areas, but also because its pollen and plant parts cause severe allergic reactions in humans and are harmful to livestock.
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Origin:
Native to the American tropics, specifically parts of Mexico, the Caribbean, and the southern United States.
Distinguishing features:
Feathery, carrot-like leaves: Pale green, deeply divided, and covered in fine hairs.
Numerous tiny white daisy-like flowers: Small (4-5 mm), creamy-white flower heads clustered at the ends of branches.
Highly branched stems: Especially after flowering, the plant becomes very bushy and branched.
Fast growth and prolific seeding: Grows quickly and produces tens of thousands of tiny seeds per plant.
Causes severe allergies: Known to cause hay fever, skin rashes, and asthma in humans.
Overall appearance:
An erect, annual herbaceous plant that can grow quite tall, with a somewhat feathery or fern-like appearance when young. It develops a vigorous, multi-branched stem after flowering, often forming dense, impenetrable stands that outcompete and exclude other vegetation.
Height:
Typically grows to between 1 and 2 metres tall, but can sometimes reach up to 3 metres under very favourable conditions.
Width:
Can spread up to 1 metre wide, with its numerous branches creating a bushy, sprawling habit.
Leaves:
Alternate, deeply lobed or dissected (pinnatifid), which gives them a distinctive feathery or fern-like appearance, quite similar to carrot leaves. They are pale green, often covered in fine hairs, and range from about 3 to 20 centimetres long and 2 to 10 centimetres wide. Leaves tend to be smaller higher up the stem.
Flowers:
Numerous, very small (about 4-5 millimetres in diameter), creamy-white, daisy-like flower heads. Each flower head consists of five tiny white ray florets (which look like small petals) and many central disc florets. They are borne in loose, branching clusters (panicles) at the ends of stems and in the leaf axils. The plant is monoecious, meaning it has both male and female flower parts on the same plant.
Flowering season (South Africa):
Flowers profusely throughout the warmer months, typically from spring through autumn (around September to May), but can flower almost year-round in frost-free regions with adequate moisture. It produces seeds very rapidly after flowering.
Fruits:
The "fruits" are actually tiny, wedge-shaped achenes (a type of dry, single-seeded fruit), about 2 millimetres long, which are enclosed within the persistent bracts (modified leaves) of the flower head.
Seeds:
Each tiny flower head produces numerous minute, black, wedge-shaped seeds (achenes) with small white scales at one end. A single plant can produce tens of thousands of seeds, which are highly viable and can remain dormant in the soil for several years, making control difficult.
Bark:
Not applicable, as it is an annual herbaceous plant with soft, green stems, not bark.
Thorns:
This species does not have thorns.
Wood:
Not applicable; it is a herbaceous plant.
Roots:
Develops a shallow, fibrous root system that allows it to quickly establish itself in various soil types, particularly disturbed ones.
Soil type:
Highly adaptable and thrives in a wide range of soil types, particularly disturbed, degraded, or nutrient-poor soils. It prefers open, sunny areas.
Aspect:
Prefers full sun for optimal growth and proliferation. It is highly tolerant of drought, high temperatures, and a variety of environmental conditions.
Edibility:
NOT EDIBLE. It is harmful to both humans and livestock.
Toxicity:
Highly toxic and allergenic.
Humans: The pollen and plant compounds (parthenin) cause severe allergic reactions, including contact dermatitis (skin rashes, blistering, itching), allergic rhinitis (hay fever symptoms like sneezing, runny nose, itchy eyes), and can exacerbate asthma. Repeated exposure can lead to chronic health issues.
Livestock: Toxic to animals if ingested, causing skin inflammation (dermatitis), mouth lesions, reduced milk production (with a bitter taste), and in severe cases, even death. It contaminates fodder and grazing pastures, making them unpalatable or harmful.
Uses:
Parthenium hysterophorus has no known beneficial uses for humans. Its impacts are overwhelmingly negative, causing significant agricultural, environmental, and human health problems wherever it invades.
Ecology:
As an alien invasive plant in South Africa, Parthenium hysterophorus is considered one of the country's most problematic weeds due to its aggressive invasiveness and wide-ranging negative impacts. It spreads rapidly and effectively, primarily through its enormous production of tiny, light seeds that are easily dispersed by wind, water, vehicles, machinery, animals (including in contaminated feed), and contaminated soil. It quickly colonises disturbed areas, roadsides, railway lines, agricultural fields, pastures, and degraded natural veld. It forms dense monocultures (single-species stands), outcompeting and displacing indigenous vegetation, significantly reducing biodiversity, and suppressing crop yields (due to its allelopathic properties, meaning it releases chemicals that inhibit the growth of other plants). Its pollen causes severe allergic reactions in humans, and the plant is toxic to livestock, contaminating grazing pastures and reducing fodder quality.
Distribution and habitat:
Widely distributed and highly invasive throughout South Africa, particularly prevalent in the warmer, eastern, and central provinces. It is very common in the Eastern Cape (especially along roadsides, disturbed areas, and agricultural land around Kenton-on-Sea), KwaZulu-Natal, Mpumalanga, Limpopo, Gauteng, and parts of North West and Free State. It invades cultivated fields, pastures, roadsides, railway lines, vacant lots, disturbed natural veld, and riparian areas.
Derivation of name:
The genus name Parthenium is thought to come from the Greek 'parthenos', meaning "virgin," possibly referring to the very small, inconspicuous female flowers or to historical medicinal uses.
The species epithet hysterophorus is derived from Greek words 'hystera' (meaning "womb" or "uterus," referring to its prolific reproductive capacity) and 'phoreo' (meaning "to bear" or "to carry").
The common name "Congress Grass" refers to its alleged introduction to India as a contaminant in imported grain from the USA during a time when the "Congress" party was in power. "Carrot Grass" comes from its feathery leaves resembling those of a carrot plant.
Historical aspects:
Parthenium hysterophorus began its global invasive spread in the mid-20th century, largely as a contaminant in imported grain (especially wheat) from North America, leading to its widespread introduction across various continents including Asia, Africa, and Australia. In South Africa, it was first recorded in KwaZulu-Natal in the 1980s and has since spread aggressively, becoming one of the most notorious and economically impactful invasive weeds due to its significant health and agricultural impacts.
NEMBA status: Category 1b invasive species. This means it must be controlled or eradicated where possible, and it is illegal to plant, propagate, import, or otherwise possess this plant without a permit.
Interesting facts:
This plant is like a super-fast seed factory! A single plant can produce tens of thousands of tiny seeds, making it incredibly good at spreading and taking over new areas!
It's known as "Congress Grass" because it supposedly arrived in India as a sneaky stowaway in grain shipments from the USA, which some people linked to political decisions at the time!
If you suffer from hay fever or skin rashes, this plant might be the culprit! Its tiny pollen can cause severe allergic reactions like sneezing, itchy eyes, and even painful skin blistering.
Farmers really dislike this plant because it reduces how much their crops grow and makes animal feed taste bad or even toxic to livestock!
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Common name
Scientific Name
Plant type:
Plant type
Plant family:
Asteraceae (star) - Order: Asterales