Reproductive Structures

The Fruit

Immediately after fertilization the pollen-receptive center of the female flower, the pistal, turns black and shrivels up; and the ovaries enlarge. Notice the black poison canals in the petals, and in the large fruit at the right:

As the fruits enlarge the petals shrivel. There is a poison canal at the base of each grove, which will later become black again. The fruit is borne on irregularly branched stalks from the sides of stems; these characteristics, plus whitish ripe fruit and subulate filaments (see flowers) are the characteristics that define poison-oak’s genus, Toxicodendron:

Mature fruit

The skin, peel, or husk of mature poison-oak fruits is stiff and crumbly; I imagine that birds remove it by rolling the fruit in their mouths before swallowing, or pulverize the husks in their gizzards. (Birds do not chew.) In any case, the husks cover the poison canals (the black lines), and the easily digested and presumably tasty pulp (the white part).