Ambrosia psilostachyaDC.

western ragweed

WFO wfo-0000137200 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h

Ambrosia psilostachya, photographed by Rich Sommer
fig. a Rich Sommer, CC BY 4.0 / 2022-04-29 / obs. 194109349
Ambrosia psilostachya, photographed by Millie Basden
fig. b Millie Basden, CC BY 4.0 / obs. 194332994
Ambrosia psilostachya, photographed by Rich Sommer
fig. c Rich Sommer, CC BY 4.0 / obs. 194878704
Ambrosia psilostachya, photographed by Rich Sommer
fig. d Rich Sommer, CC BY 4.0 / obs. 193811403
Ambrosia psilostachya, photographed by Annika Lindqvist
fig. e Annika Lindqvist, CC BY 4.0 / obs. 205663102
Ambrosia psilostachya, photographed by Lightning Star Sky / Skyler Noah Wall
fig. f Lightning Star Sky / Skyler Noah Wall, CC BY 4.0 / obs. 201349032
Ambrosia psilostachya, photographed by Rich Sommer
fig. g Rich Sommer, CC BY 4.0 / obs. 195745379
Ambrosia psilostachya, photographed by Annika Lindqvist
fig. h Annika Lindqvist, CC BY 4.0 / obs. 195052612

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 = 305 observations

Peak flowering in Sep, from 305 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 12 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 artemisiifolia var. trinitensis Griseb.
  • Ambrosia californica Rydb.
  • Ambrosia californica subsp. californica
  • Ambrosia coronopifolia Torr. & A.Gray
  • Ambrosia hispida Torr.
  • Ambrosia lindheimeriana Scheele
  • Ambrosia peruviana DC.
  • Ambrosia psilostachya var. californica S.F.Blake
  • Ambrosia psilostachya var. coronopifolia (Torr. & A.Gray) Farw. ex Fernald
  • Ambrosia psilostachya var. lindheimeriana Blank.
  • Ambrosia psilostachya var. psilostachya
  • Ambrosia rugelii Rydb.

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.