About Ageratina adenophora (Spreng.) R.M.King & H.Rob.
Ageratina adenophora is a perennial herbaceous shrub that reaches heights of 1 to 2 metres (3.3 to 6.6 ft). It produces opposite, trowel-shaped serrated leaves that measure 6–10 cm (2.4–3.9 in) long and 3–6 cm (1.2–2.4 in) wide. Its small compound flowers grow in clusters at the ends of branches, appearing in late spring and summer. Each flowerhead reaches up to 0.5 cm in diameter and is creamy white in color. After flowering, each small flower produces a small brown seed with a white feathery "parachute" structure that allows wind dispersal, similar to dandelion seeds. This species is native to Mexico, but has become an introduced species and often a noxious weed across many other regions of the world. It has caused substantial agricultural economic loss in southwestern China, where it threatens native biodiversity. It was first accidentally introduced to Yunnan around 1940, and its rapid spread is partially due to allelopathic competition with other plant species. It is also a weed in Australia, where it was first introduced to Sydney in 1904. It has spread along the coastline of New South Wales and southern Queensland, and is classified as a Class 4 Noxious Weed under the 1993 NSW Noxious Weeds Act. Ageratina adenophora has also spread to Hawaii and the mainland United States, where it is recognized as a weed in ten states across the South and Southwest. It is an invasive species in many other tropical and subtropical countries, including northeastern India, China, Sri Lanka, Nigeria, Southeast Asia, Australia, New Zealand, the Pacific Islands, the Canary Islands, Portugal (including the Azores and Madeira islands), and South Africa. The plant can spread vegetatively: its stems are able to sprout roots and grow when they come into contact with soil. Its seeds are also carried by wind or water, and easily colonize disturbed areas such as fields and land near human settlements. Seeds may also be transported by animals and within soil. Commonly called crofton weed, this plant is toxic to livestock. When horses consume crofton weed on an ongoing basis, it causes a chronic lung disease called Numinbah Horse Sickness or Tallebudgera Horse Disease in northern New South Wales and Queensland. Outbreaks of this disease occurred in Hawaii in the 1920s, and later appeared in eastern Australia and Northland, New Zealand. There are documented reports of farms losing all their horses to this condition. The disease is characterized by reduced ability to work or exercise and emphysema, with pathological findings including pulmonary interstitial fibrosis and alveolar epithelisation.
