Dr. Curt Beebe's Poison Oak Paper

Foliage Development in One Plant

Photographs at Holloway Garden in 2000

On February 9, 2000 I completed a study of "Color as an Aid to the Identification of Poison-Oak." The study concluded: "Xanthophils with a reddish purple hue are an easily learned cue to the presence of poison-oak . . . from February to mid-march."

From Christmas through January the poison-oak was dormant (see also The Seasonal Appearance of Poison-Oak: An Overview). By late March the foliage was green, and the poison-oak blended in with the other plants; quick and distant identification was no longer possible.

In order to promote the use of color for identification I took the following pictures:

January	February

The breaking of dormancy is a very distinct event. Overnight a few of the tiny, hairy, silvery, winter buds swell and crack open, revealing a glimpse of their red contents and giving the whole plant a distinctive reddish tinge. This occurred February 7 at Holloway Gardens and one day later in many other Montano de Oro locations.

February 18

Whole Plant

Crown Close-Up	Base Close-Up

There is more activity in the top of the plant; see Apical Dominance. However, the low leaves are larger and greener because they don't get as cold at night.

February 22

Whole Plant