Poison Oak (Toxicodendron diversilobum) is a fighter. This post is short: and has a simple point. Cant get rid of it at my house.
My house in coastal central CA [40 inches mean ppt, frost rare] had an undeveloped, adjacent lot when, in 1986, I moved in. Hack, Hack, Hack again later, clearing trees, grubbing stumps, planting a garden later, one would presume that any plant I had overtly targeted for eradication would now be toast, 26 yr afterwards.
Despite grubbing, despite Roundup, T. diversilobum continues to re-appear here and there. The indication I take away is that the rhizome system is very much like that of a vagile invader such as Convolvulus arvensis; in which, when fragmented, tiny little fragments maintain, then gain, and continue demographic existence, as if awaiting a relaxation of control. In my neighborhood, T. diversilobum assumed the two known growth forms: 1) lianas which grow via attachment roots (cf. Hedera, Araliaceae) to 100 feet in the crown of old-growth Sequoia sempervirens, or 2) bushy, highly branched ‘shrubs’. The overall indication I intend with this post is that the phenotypic plasticity of T. diversilobum seems to be under genetic control. General purpose genotype?
Merits study with molecular methods.