Bitter weed

Helenium amarum
Herb
Alternate
Simple
Yellow
Green

Native to south-eastern USA and Mexico, bitter weed is a compact annual with small yellow flowers. Bitter weed is poisonous to livestock and competes with pasture and native vegetation. In Queensland, it has been found at only 1 location, near Mount Tarampa in the Lockyer Valley.

Bitter weed is a prohibited invasive plant under the Biosecurity Act 2014

Common names 
Also known as: yellow sneeze weed, Sneezeweed, , bitter sneezeweed, , fine-leaved sneezeweed,
Family 
Asteraceae
Deciduous 
No
Flowering time 
Most flowering occurs over spring and summer
Native/Exotic 
Exotic
Origin 
Native to the United States and Mexico
Notifiable 
Yes
State declaration 
Category 1
Council declaration 
As per State Declaration
Known distribution 

H. amarum was first detected in Queensland in 1953 near Mt Tarampa (south-eastern
Queensland), the only known detection of this plant in Australia. It was subsequently the
target of an eradication program lasting more than 40 years. In 2002, complete eradication
was claimed, after extensive searches failed to detect the plant. However, more recent
surveillance (in 2007) confirmed the existence of small numbers of specimens. These have
been removed and the site is being monitored.

Habitat 

Climatically, H. amarum appears well suited to warm temperate and perhaps subtropical
areas, where annual rainfall does not exceed 1000 mm. As such, subcoastal and inland
areas of southern and perhaps central Queensland are most at risk of invasion. This
species is not adapted to tropical areas. Within its native range, H. amarum is a common
and opportunistic weed of open fields, roadsides and waste places. Hence, it is predicted
to invade similar habitats in southern Queensland

Habit 

Annual herb up to 60cm tall, compact and bushy under favourable conditions.

H. amarum is a troublesome plant within its native range in the United States. For example, in Texas some grazing paddocks become almost completely covered by this species. When ingested by dairy cattle, it imparts a bitter taste to their milk, rendering it undrinkable. It is also a livestock poison, causing weakness, diarrhoea and vomiting to animals that consume it, including sheep, cattle and horses. H. amarum was listed as one of the few species in Helenium that has caused mortality of sheep in Texas. Competes with native vegetation.

Stem and leaves 

An annual herb up to 60 cm tall. Its stems are smooth, erect and branching in the upper portion. The leaves are numerous, smooth, thread-like and without petioles. Leaves are arranged alternately along the stems and tend to crowd the main stem and branches. 

Flowers and fruits 

Flower heads are about 2 cm in diameter. Ray flowers are yellow with toothed tips and surround a dome-shaped mass of yellow disk flowers. Seeds are about 1 mm long, reddish-brown, hairy along the edges and wedge-shaped, bearing bristletipped scales at their tops. Two varieties of this plant differ only in their flower colour: one is pure yellow; the other is yellow with a red-brown centre

Reproduction and dispersal 

Reproduces from seeds. Specimens can flower and produce mature seed very quickly, when only eight weeks old. Mature seeds are
non-dormant and germinate readily in sunlight over a wide range of temperatures. The scented flowers are hermaphroditic (have both male and female reproductive structures) and are pollinated by insects such as bees and butterflies