Toxicodendron

Cashew Family-Anacardiaceae

(www.fs.fed.us/database/feis/plants/shrub/toxrad/introductory.html

by Roger Hilten

photo by Roger Hilten

Description

• toxic-all contain the chemical urishiol that causes mild to severe dermatitis (Woodward, 1985). Urishiol is an oily phenol that occurs in the leaves and bark of all members of Toxicodendron (Eastman, 1995).
• most are trifoliate (excluding Poison Sumac-T. vernix)
• cause mild to serious skin rashes
• absent in very cold or tropical climates (Ridley, 1930).

Species List

• T. radicans i.e. poison ivy
• T. vernix i.e. poison sumac
• T. toxicarium i.e. Eastern poison oak
• T. diversilobum i.e. Western poison oak
• T. rydbergii i.e. nonclimbing poison ivy

Individual Characteristics

T. radicans- This is true poison ivy that is best known for its nature to climb the trunks of trees in the form of a furry vine. Its leaves are also well-known for their trifoliate structure. Less-known aspects include greenish-white flowers and aerial roots which the vine uses to climb (Frankel, 1991).

• T. vernix- This family member, poison sumac, breaks away from the trifoliate leaf-structure. "The branch has four alternate, pinnately compounded leaves that are lobeless and even edged" (Frankel, 1991).

• T. toxicarium- This is Eastern poison oak without aerial roots i.e. cannot climb. It grows as a short shrub having the same trifoliate leaves as poison ivy, but with more rounded lobes. Both poison ivy and oak both have fruit and drupes in axillary clusters. These, along with the leaves have a fine layer of hairs making the plant look velvety (Frankel, 1991).

• T. diversilobum- This is western poison oak that is strictly a pacific coast species. Unlike eastern poison oak, this one has aerial roots that allow it to climb and form a vine. This type also has trifoliate leaves but with great variation in lobing making its leaves look very oak-like. "Axillary clusters look much like those of eastern Toxicodendrons" (Frankel, 1991).

• T. rydbergii- This is the more northerly species of non-climbing poison ivy which grows as shrub since it also lacks aerial roots. This species has trifoliate leaves that are spoon shaped (Frankel, 1991).

References

Eastman, John. 1995. The Book of Swamps and Bog. Stackpole Books. Mechanicsberg, PA.

Frankel, Edward, Ph.D. 1991. Poison Ivy, Poison Oak, Poison Sumac and their relatives; pistachios, mangoes, cashews. The Boxwood Press. Pacific Grove, CA. (call #QK 495.A498 F73 1991). 98pages.

Ridley, Henry N. 1930. The Dispersal of Plants Throughout the World. Willam Clowes and Sons.

Woodward, Lucia. 1985. Poisonous Plant; A Color Field Guide. David and Charles. New York.

(www.fs.fed.us/database/feis/plants/shrub/toxrad/introductory.html