Canadian fleabane
Erigeron canadensis
Family · Asteraceae · Harmless
The bright green upright wand rising from any tarmac crack and making a pyramid of minute heads at the top. It was the first American plant to invade Europe, in the seventeenth century.
Town and roadside · Roadsides and waste ground · Fields and pasture · Streams and ditches
Also known ashorseweed, butterweed
How to tell it
A single, upright, bright green, almost hairless stem, with narrow toothed leaves running up close to the top. The flowers gather in a broad pyramid panicle, the main axis always above the side branches, unlike hairy fleabane. Minute heads with extremely short white rays.
What it is confused with
Flax-leaf fleabane
Erigeron bonariensis
Look at the top of the plant: on the Canadian one the main axis stands above everything, in a pyramid; on the hairy one the side branches overtop it and give a dishevelled outline. And the hairy one is grey, this is bright green.
Open sheet →What it is for
No use to recommend. A single plant produces over a hundred thousand seeds that fly for kilometres, and it is among the world's first species to have evolved glyphosate resistance.