Japanese sunflower

Tithonia diversifolia
Shrub
Opposite
Simple
Yellow
Green

A robust and bushy plant, that can be short-lived or long-lived, growing up to 3 m tall. Its leaves have three or five pointed lobes and scalloped margins. Its large yellow daisy-like flower-heads are about 10 cm across and have yellow centres. Its seeds (6-8 mm long) are topped with a ring of scales and two awns.

Common names 
Also known as: Japanese sunflower, giant Mexican sunflower, Japanese sunflower, tree marigold, shrub sunflower,
Family 
Asteraceae
Deciduous 
No
Flowering time 
Year Round
Native/Exotic 
Exotic
Origin 
Native to eastern Mexico and Central America (i.e. Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama). Despite its common name, this species is not native to Japan.
Notifiable 
No
Council declaration 
Class R – Reduce populations
Known distribution 

Japanese sunflower (Tithonia diversifolia) is widely naturalised in the coastal districts of Queensland and northern New South Wales. It is also present on Christmas Island. Also widely naturalised throughout the tropical and sub-tropical regions of the world, including south-eastern USA (i.e. Florida and Texas) and several Pacific islands (i.e. the Cook Islands, the Galapagos Islands, Fiji, French Polynesia, New Caledonia, Niue, Palau, Western Samoa, Tonga and Hawaii).

Habitat 

A common weed of roadsides, railway lines, creekbanks, disturbed sites, waste areas, embankments, hillsides and neglected suburban lots in tropical, sub-tropical and warmer temperate regions.

Habit 

A robust and short-lived (i.e. annual) or long-lived (i.e. perennial) plant with upright (i.e. erect) stems forming shrubby bushes usually growing 2-3 m tall, but occasionally reaching up to 5 m in height.

Impact and control methods 

Japanese sunflower (Tithonia diversifolia) is regarded as an environmental weed in Queensland and New South Wales. It was also recently listed as a priority environmental weed in at least one Natural Resource Management region.

Stem and leaves 

The stems are slightly ridged (i.e. striate) and hairy (i.e. pubescent) when young. The alternately arranged leaves are borne on stalks (i.e. petioles) 2-10 cm long. The leaf blades (6-33 cm long and 5-22 cm wide) have tapered (i.e. cuneate) bases and 3-7 pointed lobes with scalloped (i.e. crenate) or toothed (i.e. serrate) margins. These leaves are finely hairy (i.e. puberulent) and greyish-green in colour.

Flowers and fruits 

The large flower-heads (i.e. capitula) are borne in small groups at the ends of the leafy branches, on stalks (i.e. peduncles) 7-30 cm long. These flower-heads (5-15 cm wide) look like sunflowers, but have yellow centres (3-5 cm across). They have 7-15 bright yellow 'petals' (i.e. ray florets) that are 4-7 cm long and 9-16 mm wide, each with three small teeth at their tips. There are also numerous (80-120) tiny yellow flowers (i.e. tubular florets) in the centre of the flower-heads and they are surrounded by several rows of green bracts (i.e. an involucre). Flowering occurs during spring, but mainly during autumn and early winter (i.e. from April to June). The 'seeds' (i.e. achenes) are 4-8 mm long and topped with a ring (i.e. pappus) of scales and two awns (about 5 mm long). These 'seeds' are covered in close-lying hairs (i.e. they are appressed pubescent), blackish in colour, and are somewhat four-angled.

Reproduction and dispersal 

This species reproduces by seed.The seeds may be dispersed by animals, water and in clothing, They may also be spread in dumped garden waste and contaminated agricultural produce.

Similar species 

Japanese sunflower (Tithonia diversifolia) is similar to Mexican sunflower (Tithonia rotundifolia), wild sunflower (Helianthus annuus) and crownbeard (Verbesina encelioides). These species can be distinguished by the following differences: Japanese sunflower (Tithonia diversifolia) has leaves with 3-7 pointed lobes. Its flower-heads have bright yellow centres and yellow 'petals (i.e. ray florets) 4-7 cm long.Mexican sunflower (Tithonia rotundifolia) has leaves without lobes or with rounded lobes. Its flower-heads have bright yellow centres and orange or reddish 'petals' (i.e. ray florets) 2-3.5 cm long.wild sunflower (Helianthus annuus) has leaves without lobes. Its flower-heads have orange-brown to dark brown centres and yellow 'petals' (i.e. ray florets) 2-3 cm long.crownbeard (Verbesina encelioides) has leaves without lobes. Its flower-heads have bright yellow centres and yellow 'petals' (i.e. ray florets) 1-2 cm long.