Toxicodendron rydbergii(Small ex Rydb.) Greene

western poison ivy

WFO wfo-0001049958 Accepted WFO 2026-06 8 photographs CC0 / CC BY

Plate 1 figs. a–h

Toxicodendron rydbergii, photographed by Étienne Léveillé-Bourret
fig. a Étienne Léveillé-Bourret, CC BY 4.0 / 2022-05-31 / obs. 205347672
Toxicodendron rydbergii, photographed by rboles
fig. b rboles, CC BY 4.0 / obs. 202063183
Toxicodendron rydbergii, photographed by Erica Barkley
fig. c Erica Barkley, CC BY 4.0 / obs. 205318872
Toxicodendron rydbergii, photographed by agbelliveau
fig. d agbelliveau, CC0 1.0 / obs. 204007867
Toxicodendron rydbergii, photographed by Carol Ann Vermeer
fig. e Carol Ann Vermeer, CC BY 4.0 / obs. 205054268
Toxicodendron rydbergii, photographed by Ben Keen
fig. f Ben Keen, CC0 1.0 / obs. 200623037
Toxicodendron rydbergii, photographed by scaup
fig. g scaup, CC BY 4.0 / obs. 200769878
Toxicodendron rydbergii, photographed by Liren Varghese
fig. h Liren Varghese, CC BY 4.0 / obs. 202762640

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 = 911 observations

Peak flowering in Jun, from 911 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 15 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.

  • Rhus radicans subsp. rydbergii (Small ex Rydb.) McNeill
  • Rhus radicans var. rydbergii (Small ex Rydb.) Rehder
  • Rhus radicans var. vulgaris (Michx.) DC.
  • Rhus rydbergii Small ex Rydb.
  • Rhus toxicodendron var. rydbergii (Small ex Rydb.) Garrett
  • Rhus toxicodendron var. vulgaris Michx.
  • Toxicodendron desertorum Lunell
  • Toxicodendron fothergilloides Lunell
  • Toxicodendron longipes Greene
  • Toxicodendron macrocarpum Greene
  • Toxicodendron pumilum Greene
  • Toxicodendron punctatum Greene
  • Toxicodendron radicans subsp. rydbergii (Small ex Rydb.) Á.Löve & D.Löve
  • Toxicodendron radicans var. rydbergii (Small ex Rydb.) Erskine
  • Toxicodendron rufescens Greene

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.