Wildflowers of Toronto's High Park​​

Ragweeds 
Family: Composite/Aster
Genus: ​​Ambrosia
Native to Ontario 
Annual

​Ragweed, common
A. artemisiifolia

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.
​Ragweed, giant
A. trifida

Blooms: August to October
Habitat: Rich moist soil

Height: up to 4.5 m

​Leaves: Opposite, with 3-5 palmate lobes

​Male flower heads: terminal spikes.  Female flower heads grow in leaf axils.