Wildflowers of Toronto's High Park​​

Ragweed, common
​Ambrosia artemisiifolia

​Family: Composite/Aster
Native to Ontario

Blooms: August to October
Habitat: Waste places

Height: up to 1 m

​Leaves: fern-like

Female flower heads: single, inconspicuous, in axils of upper leaves. 

Male flower heads: Long terminal spike bearing up to 50 florets which produce vast quantities of pollen.  This is spread by wind and is a major cause of hay fever.