Ambrosia trifidaL.

giant ragweed

WFO wfo-0000114875 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h

Ambrosia trifida, photographed by Ryan Sorrells
fig. a Ryan Sorrells, CC BY 4.0 / 2022-05-26 / obs. 200858122
Ambrosia trifida, photographed by Violet T.
fig. b Violet T., CC BY 4.0 / obs. 204974152
Ambrosia trifida, photographed by Howard Williams
fig. c Howard Williams, CC BY-SA 4.0 / obs. 205233724
Ambrosia trifida, photographed by Alan Prather
fig. d Alan Prather, CC BY 4.0 / obs. 201938911
Ambrosia trifida, photographed by Susan Berry
fig. e Susan Berry, CC0 1.0 / obs. 204665132
Ambrosia trifida, photographed by Joseph Aubert
fig. f Joseph Aubert, CC BY 4.0 / obs. 200908690
Ambrosia trifida, photographed by Joseph Aubert
fig. g Joseph Aubert, CC BY 4.0 / obs. 200392361
Ambrosia trifida, photographed by Joseph Aubert
fig. h Joseph Aubert, CC BY 4.0 / obs. 200401747

Every figure is a research-grade observation under CC0, CC BY or CC BY-SA, rehosted with the photographer’s name, the licence and the observation it came from. Photographs under a NonCommercial licence are excluded from this site and are never stored, which costs us a great many pictures and is not negotiable.

Confused withby our own model

These are not lookalikes we guessed at. Each one is a species our identification model genuinely mistook for this plant, and how many times. The error rate is published.

Flowering n = 827 observations

Peak flowering in Aug, from 827 community-annotated observations worldwide. This is a global aggregate, not a forecast for your garden: the same species flowers on different dates in different hemispheres, and citizen-science records cluster near cities, at weekends, and in spring. Where a species has fewer than 30 annotated records we do not draw this chart at all.

Also published as 6 synonyms

A synonym is not an error. It is a record of botanists disagreeing, in print, about where this plant belongs. Each of these was somebody’s considered answer.

  • Ambrosia integrifolia Muhl. ex Willd.
  • Ambrosia trifida f. trifida
  • Ambrosia trifida subsp. trifida
  • Ambrosia trifida var. aptera Kuntze
  • Ambrosia trifida var. heterophylla Kuntze
  • Ambrosia trifida var. polyploidea J.Rousseau

Sourcesevery claim on this page

  1. World Flora Online Plant List. accepted name, authority, classification. CC0. Retrieved 2026-07-12.
  2. iNaturalist. photographs and flowering annotations, CC0 / CC BY / CC BY-SA only. per photograph. Retrieved 2026-06-27.

We publish what we can source and we say so when we cannot. This page has no care advice, no toxicity claim and no native range, because we do not yet have those from a source we can cite.