Plants: erect, perennial, 1'-3' tall shrub with 1 to a few branches; stems woody; from colony-forming rhizomes
Leaves: alternate, stalked, usually near the top of the stem, shiny, smooth, 3 parted, the widely-oval leaflets with a pointed tip
Flowers: white, 5-parted; inflorescence a 4"-16" elongated, branched cluster (cyme) with usually less than 25 stalked flowers; blooms June-Aug.
Fruits: smooth, white to yellow berry
Habitat: full to partial sun; woods edges, openings, prairies
Hazardous: Careful, this plant is hazardous!
Conservation Status: Native - potentially invasive
This species is a low shrub forming dense patches along the ground usually no more than a meter tall. The leaflets are usually folded along the midvein, while in T. radicans they are flat. Unless notes describing the plant’s habit are present, it can sometimes be difficult to identify herbarium specimens of our two species. Although the petioles of T. rydbergii are said to be glabrous, many of our plants have petioles that are sparsely to moderately pubescent with short, incurved hairs. These hairs are never as dense or long as those of T. radicans and whether hairy plants of T. rydbergii represent hybrids between the two is unknown. The taxonomy of this group is complicated and T. rydbergii was once included in T. radicans.
Western poison-ivy is more widespread in the state and is found farther north than T. radicans. The former has clearly benefited from human-induced changes on the landscape.