Rhus diversiloba

Pacific poison oak

Anacardiaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (Flowering plants). Class - Magnoliopsida. Order - Sapindales. Family - Anacardiaceae (Sumac family). Genus -Toxicodendron Mill. Species - Toxicodendron diversilobum Torr. & A. Gray

Ecology: Pacific poison oak Pacific poison-oak occurs in mixed evergreen forests, woodlands, chaparral, coastal sage scrub, and riparian zones. It is the most widespread shrub in California. Associates in mixed evergreen forests include Pacific madrone (Arbutus menziesii), sugar pine (Pinus lambertiana), bigleaf maple (Acer macrophyllum), tanoak (Lithocarpus densiflorus), California bay (Umbellularia californica), and chinquapin (Chrysolepsis chrysophylla)

Identification

Pacific poison oak (Rhus diversiloba), is a many-stemmed, deciduous, native shrub or woody vine.Shrubs are erect with stems from 2 to 6 feet (1-2 m) tall. Vine stems commonly reach 10 to 30 feet (3-10 m), but may be as long as 100 feet(30 m). As a vine, Pacific poison-oak climbs trees or other support by adventitious roots and/or wedging stems within grooves or crevices of the support. Leaves trifoliate; leaflets ovate to obovate, sinuate to deeply lobed, rounded to acute, 3-7 cm. long.

Threats

Fire effects: Pacific poison oak sprouts vigorously from the root crown and/or rhizomes after fire. It sprouts in the first postfire growing season, and for several years thereafter. Pacific poison-oak sprouts were noted the September following the July, 1985, Wheeler Fire on the Los Padres National Forest, California. The wildfire had spread into a riparian zone containing Pacific poison-oak; prefire Pacific poison-oak density was unknown. By postfire year 3, Pacific poison-oak sprouts dominated most burn plots in the riparian zone.Pacific poison-oak also establishes from seed after fire.

Reproduction

Pacific poison-oak reproduces vegetatively by sprouting from the rhizomes and root crown after disturbance such as fire or browsing has removed topgrowth.It also reproduces by layering when vine stems contact the ground. Pacific poison-oak seeds are dispersed by birds. Seedlings occur both before and after fire, suggesting that the seeds do not depend upon fire for scarification. The seeds have a gummy seedcoat which leaches off very slowly, resulting in delayed germination.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Burke Museum of Natural History and Culture
Burke Museum. 2016. Abies amabilis [Online]. University of Washington.