Toxicodendron rydbergii (Small ex Rydb.) Greene   (redirected from: Toxicodendron radicans var. rydbergii)
Family: Anacardiaceae
western poison ivy
[Rhus radicans var. rydbergii (Small ex Rydb.) Rehd.,  more]
Toxicodendron rydbergii image
Max Licher  
PLANT: Subshrubs or shrubs spreading and rhizomatous, to 3 m tall. LEAVES: with glabrous petioles much longer than terminal leaflet, to 17 cm long; leaflets broadly obovate, 1-1.5 times as long as broad; margins crenate to serrate, 2n = 30. NOTES: Moist but often sunny sites along canyons and at seeps and springs, from the Sonoran Desert to mixed conifer forest; all AZ cos. except Pima, Pinal, Santa Cruz, and Yuma; 455-2575 m (1500-8500 ft); Apr-Jun; across s Canada and n US (e of the Cascades), s through Rocky Mountains and Great Plains to AZ, NM, and w TX.
Shrub or subshrub 30 cm to 2 m tall Leaves: alternate, often borne near ends of stems on a usually hairless stalk 1.5 - 25 cm long, with three leaflets (trifoliate). Flowers: borne on unbranched or few-branched small clusters in leaf axils, each cluster usually having fewer than 25 flowers. Fruit: fleshy with a center stone (drupe), densely clustered, erect, stalkless or nearly so, cream to yellowish, 4 - 7 mm thick, spherical, hairless, sometimes persisting through winter. Leaflets: stalked (middle leaflet stalk longest), 3 - 15 cm long, 2 - 11 cm wide, broadly egg-shaped or almost four-sided to nearly circular with a rounded to nearly squared base and a pointed tip, unevenly toothed or wavy, hairless on both surfaces or with appressed hairs beneath and a tiny line of curly hairs on the midvein's upper surface. Fall color is yellow to orange, rarely bronze to red. Form: mostly upright, single-stalked or few-branched, forming colonies by runners but lacking aerial roots.

Similar species: Toxicodendron radicans is a vine or shrub with aerial roots, narrower leaflets, and an open cluster of fruit hainging downward. The hybrid between Toxicodendron radicans ssp. negundo and Toxicodendron rydbergii is intermediate in characteristics, and can be distinguished from T. rydbergii because it sometimes grows as a vine or has aerial roots, occasionally has somewhat hairy leafstalks, and has narrower leaflets. A few tree and shrub species may be mistaken for T. rydbergii. Acer negundo and Staphylea trifolia have opposite leaf arrangements. Ptelea trifoliata has alternate leaves, but the leaflets are all very short-stalked with non-toothed to finely toothed margins.

Flowering: late May to late June

Habitat and ecology: A northern and western species found scattered in fields, woods, dunes, and open, sunny areas.

Occurence in the Chicago region: native

Notes: Avoid touching this plant, as it contains a toxic compound called urushiol. Do not burn it, as the toxin is released into the air and can be inhaled. After contact with urushiol, a person sesitive to the toxin becomes itchy, and within 24 - 48 hours the skin blisters and reddens. If tools or clothing have been contaminated, they should be washed with hot water and soap.

Etymology: Toxicodendron means "poison tree." Rydbergii is named after Per Axel Rydberg, an early 20th century member of the New York Botanic Garden and expert on the flora of the western United States.

Author: The Morton Arboretum

Toxicodendron rydbergii image
Max Licher  
Toxicodendron rydbergii image
Max Licher  
Toxicodendron rydbergii image
Max Licher  
Toxicodendron rydbergii image
L.R. Landrum  
More Images        Web Links       View Parent Taxon       Close window