Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
(unranked): Asterids
Order: Asterales
Family: Asteraceae
Tribe: Eupatorieae
Genus: Ageratina
Species: A. adenophora
Binomial name: Ageratina adenophora
Synonyms: Eupatorium adenophorum, Eupatorium glandulosum, Eupatorium glandulosum, Eupatorium pasadenense
Common names: Mexican Devil, Crofton weed, Sticky snakeroot, Cat weed, Catweed, Hemp agrimony, Sticky agrimony, Sticky eupatorium, White thoroughwort

Ageratina adenophora long-lived, herbaceous plant that is native to Mexico and possibly Central America. It now naturalised in Australia, southern Europe, Africa, Asia, south-western USA and many oceanic islands in the Pacific Ocean including New Zealand. This species is a weed of roadsides, railways, pastures, fence-lines, disturbed sites, forest margins, waste areas and riparian zones. It is also commonly found in urban open spaces, open woodlands and rainforest clearings.

Ageratina adenophora is an erect, many-stemmed herb to subshrub growing up to 1-2 m. Stems often die back in winter. They are densely covered in stalked sticky hairs and are usually purple, become woody with age. The branches are in opposite pairs. The drooping stems can take root where they touch the ground.
The leaves are diamond-shaped (4-15 cm long and 3-9 cm wide) with irregularly round-toothed edges and are in opposite pairs along the stems. They are borne on 1-6 cm long (petioles.
From August to January dense clusters of small, white flowers (5-7 mm diameter) are produced, followed by 5-angled black seeds (1.8 mm long). Seeds are spread by wind, water, animals, vehicles and by contaminated agricultural produce.
Ageratina adenophora is toxic to livestock. Ongoing consumption of it by horses leads to chronic lung disease, known as Numinbah Horse Sickness or Tallebudgera Horse Disease. Outbreaks have occurred in Hawaii in eastern Australia and Northland in New Zealand. There are reports of farms losing all their horses to the condition. It is typified by an impaired ability to work or exercise and emphysema. Pathological findings include pulmonary interstitial fibrosis and alveolar epithelisation.

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1-Ageratina adenophora (Flower) 2.jpg

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Thanks to Wikipedia for text and information: