Crofton weed
Ageratina adenophora
Family · Asteraceae · Poisonous
Read this before the sheet
This plant, or one that resembles it, is dangerous. Identifying is not authorising: no app has the authority to tell you that you may eat or touch a plant.
Emergency
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The sticky Mexican shrub covering road banks and levada walls in Madeira, with clouds of fluffy white flowers at the end of winter.
Roadsides and waste ground · Streams and ditches · Walls and rocks · Oak woods
Also known assticky snakeroot, Mexican devil
How to tell it
A subshrub one to two metres, with reddish stems covered in glandular hairs that make it sticky to touch. Opposite leaves, diamond or triangular, coarsely toothed with three veins from the base. Small white rayless heads gathered in dense fluffy corymbs.
What it is confused with
Hemp agrimony
Eupatorium cannabinum
Both make fluffy corymbs and belong to the same tribe. Hemp agrimony has pale pink flowers and leaves divided into three segments; Crofton weed has white flowers and entire diamond leaves, and is sticky. Both carry alkaloids that damage the liver.
What it is for
None
It contains pyrrolizidine alkaloids and a toxin causing severe lung disease in horses, known in Australia as Numinbah horse sickness. It is among the world's hundred worst invaders and in Madeira occupies practically every mid-altitude verge.
The law says
A listed invasive alien species in Portugal. Do not plant or propagate it.
Where it occurs
Each square is an area with recorded observations of this plant. The lighter background is the set of areas where any of the entries has been observed, and serves as a reference. Note what this is not: it is not where the plant lives, it is where people record it, so trails and towns always look fuller than the mountains. Data from GBIF.
Sources
Community
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