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Mexican Sunflower (Tithonia diversifolia)

Tithonia diversifolia is an annual (or perennial, depending on the growing region) tall bush herb that can grow up to 3 meters tall. 

The plant can be identified by its showy, daisy-like orange (sometimes yellow) flowers that bloom in clusters.  

The flowers bloom in spring but are more active in autumn and early winter. In areas like East Africa, the plant’s flowers bloom during the rainy season. 

Scientific Classification

  • Domain: Eukaryota
  • Kingdom: Plantae
  • Phylum: Tracheophyta/ Magnoliophyta
  • Subphylum: AngioSpermae
  • Class: Magnoliopsida
  • Order: Asterales
  • Family: Asteraceae
  • Genus: Tithonia 
  • Species: Tithonia diversifolia
  • Common Names: Mexican sunflower, Japanese sunflower, Mexican tournesol, Bolivian sunflower, tree marigold, shrub sunflower, giant Mexican sunflower, and wild sunflower. 

Nativity & Distribution

Mexican sunflower is native to Mexico and parts of Central America. However, it is a widespread species that can be found in over 70 countries worldwide, including: 

  • USA (Hawaii, Texas, Florida)
  • South America (Chile, Colombia, Brazil)
  • Asia (China, India, Myanmar, Thailand, Japan, Philippines) 
  • Africa (Kenya, Uganda, South Africa, Madagascar, Tanzania, Angola, Nigeria)
  • Oceania (Australia, New Zealand) 
  • Pacific islands (Fiji, Vanuatu, French Polynesia). 

Physical Characteristics

The Mexican sunflower can grow 2-3 m in height
The Mexican sunflower can grow 2-3 m in height. Image: wiktrop/tlbourgeois
  • Leaves: Sub-ovate leaves with serrated margins. 
  • Stems: Sturdy, woody stems. They can grow to between 2 and 3 meters tall.
  • Fruits: A one-seeded black achene. 
  • Flowers: Daisy-like orange to yellow flowers with tiny tubular florets at the center. 
  • Roots: Tap root system with several fine secondary roots. 

The Mexican sunflower is a fast-growing annual, sometimes perennial, herb that grows upright and can reach 2-3 m in height. Its conspicuous, daisy-like orange flowers make it easy to identify. 

The plant has woody, herbaceous stems, which are cylindrical and hollow inside. The stems are also slightly ridged and hairy when they are young. 

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Tithonia diversifolia stems are green when the plant is young but turn reddish-brown as it ages. They are fast-growing and can quickly form thick, shrubby bushes. 

The leaves are arranged in an alternate pattern on the stem and borne on petioles about 2-10 cm long. They are also large, about 6-33 cm long and 7-22 cm wide. 

The Mexican sunflower leaves are greyish-green in color and have fine hairs. Each leaf blade has a tapered base and 3-7 pointed lobes with serrated margins. 

The leaves on the lower part of the stem tend to fall off as the plant matures and grows taller, giving it a leggy look. 

Tithonia diversifolia flowers are daisy-like, 10-30 cm long, and 5-15 cm wide. The flower heads have 7-14 bright orange to yellow petals (ray florets), with a central disc consisting of 80 to 120 tiny yellow flowers (tubular florets). 

The flowers form clusters at the tip of leaf branches, perched on stalks, about 7-30 cm long. The flower heads are also honey-scented, which helps attract butterflies and bees for pollination. 

Reproduction, Dispersal, & Life Cycle

  • Life Cycle: Annual (sometimes perennial).
  • Seeds: Can produce 80,000-160,000 annually. 
  • Climate: Grows well in areas with a tropical climate. 
  • Dispersal: Wind, water, livestock, vehicles, and movement of people. 

Tithonia diversifolia is a prolific seeder, with a single mature plant producing up to 160,000 seeds annually. The seeds are achenes, quadrangular in shape, 5-6mm long, and 1.5-2mm wide. 

The blackish seeds are topped with a ring (pappus) and have two bristles (awnings). They are also covered in close-lying hairs, which allows them to be easily dispersed by winds over long distances. 

Mexican sunflower seeds are easily dispersed by wind, water, animals, people, and vehicles. They germinate readily all year round on the soil surface or in shallow soil. 

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Dormant seeds in the soil can also remain viable for up to four months. During this period, soil disturbances, such as tillage, can lead to a flush of germination. 

While Tithonia diversifolia usually reproduces sexually, it can also reproduce vegetatively through stem cuttings. 

Uses

  1. Used as a landscape ornamental plant or a hedge plant. 
  2. Used as a herbal medicine to treat bruises and skin diseases, relieve stomach aches, and as a diuretic. 
  3. It is used as a green mature or for compost (the leaves and stems are high in nitrogen, phosphorus, and potassium). 
  4. It is used as fodder for livestock or as chicken feed. 
  5. It is used for soil erosion control, mulching, fuel, and as a building material. 
  6. The leaves and stems of the plant are used as a pesticide against aphids, whiteflies, and weevils. 

Impact on Environment

The aggressively growing weed forms thick bushes that outcompete native vegetation
The aggressively growing weed forms thick bushes that outcompete native vegetation. Image: Facebook/anniehayes

Tithonia diversifolia is listed as an invasive species in the Global Invasive Species Database and is considered a weed in several countries, such as South Africa and Australia. 

It is an aggressive growing plant that can invade several areas, from open grounds to forest edges, riverbanks, pastures, disturbed sites, and more. 

Once it infests an area, it can form thick bushes, outcompeting or displacing the native vegetation. Mexican sunflowers can invade crop fields, reducing yields, especially for rice, maize, and sorghum. 

A study published in 2017 also found the plant to be toxic to several crops, including rice, sorghum, maize, lettuce, and cowpea.  

While Tithonia diversifolia can be used as a fodder crop, it can also invade pastures and grazing areas, reducing the available forage for livestock. 

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In addition, its thick bushes can be a nuisance on pathways and roadsides. 

Control

You can control the spread of the Mexican sunflower though these methods:

Natural methods 

    Tithonia diversifolia is a highly invasive species that can spread rapidly and is a nuisance to contain. Therefore, the method for controlling this weed is prevention. 

    When prevention fails, you can attempt other control solutions. For example, you can pull small infestations of the Mexican sunflower from the ground. 

    You can also slash the plant before it starts producing flowers and seeds. 

    However, to prevent further propagation, you should properly dispose of all the cut stems in a plastic bag or burn them in the field (this can produce nutrient-rich organic matter that can enrich the soil). 

    Chemical control

      Some herbicides that can control Tithonia diversifolia infestation include 2,4-D (a post-emergent) and atrazine + metolachlor (a pre-emergent) for crops like maize. Other herbicide options include: 

      • Metsulfuron-methyl + Aminopyralid can be applied (alongside a surfactant) to infested pastures with a spray gun. Livestock should not feed on pasture for about 56 days. 
      • Metsulfuron-methyl – can be applied to actively growing Mexican sunflower plants before seeding. 
      • Picloram + Triclopyr + Aminopyralid (Grazon Extra) – can be applied as a foliar spray before the plant produces flowers. 
      • Picloram + Aminopyralid (Vigilant II) can be applied using the cut stump method (cutting the stems and applying the herbicide to the stumps immediately after). 
      • Triclopyr + Picloram – can be applied as a foliar spray before the plant flowers. 

      Biological control methods. 

        Research conducted in South Africa has identified Physonota maculiventris, a leaf-eating beetle, as an effective biological agent against Tithonia diversifolia

        The Mexican sunflower is also vulnerable to slugs and snails, which feed on it and leave holes in the foliage. The slugs and snails often attack the plant during the rainy season.