This is one plant we all should get to know in all of its varying phases.  Leaflets usually emerge red and are three in a cluster; flowers are tiny and white/yellow; berries are clustered and off-white; stems are dull brown with conspicuous sloped scars where previous leaves were attached.  Plants shown here are typical: clustered, upright, and about two feet tall, but they do grow to about six feet tall in our area.  In the East, Poison Ivy can have a main stem of several inches in diameter and climb high into trees as a hairy vine.

In the dry Southwest, Poison Ivy is nowhere near as common as in the East, but it is just as toxic.  Look out for it even in very dry surroundings, for even though it may not be found for miles along a dry trail, when you take your lunch break at the base of cliffs, near seeps and springs, or near an alcove hanging garden you are apt to find it.  The juices of all parts of the plant are active any time of the year and cause severe itching in most people.  As is true of many allergic reactions, each person's reaction to Poison Ivy can change during their lifetime.

"Toxicodendron" is Greek for  "poison tree".  "Rydbergii" is for Per Axel Rydberg, one of the most eminent of 19th and early 20th century botanists. (More biographical information.)