Variations in Foliage

Genetics 

Poison-oak has many genes for leaf characteristics, which account for some of the leaflet variability seen, and may assist the plant in its adaptation to microclimates. For example, here are three branches collected on the same day from plants with full sun exposure growing within fifteen feet of each other at the Overlook on Upper State Park Road:

And here’s an example of deep “sinuses”. The notches on the sides of the leaflets usually go less than half way to the central vein. This collection consists of six of the first seven consecutive terminal leaflets growing on one stem, in filtered partial sun. The sixth leaflet was curled and could not be flattened out for the picture:

Thirty feet away the genotype was still present. Here are two of ten leaflets collected in this adjacent site. There was stronger partial sunlight:

Here’s a leaflet with no sinuses. Growing in moderate shade, it is also the longest leaflet I’ve found.

And here’s the most oak like poison-oak I’ve found. It resembles the leaves of the valley oak somewhat. The valley oak is on the left side of the picture: