Was particularly interested to read Loretta's, Tiffany's and Frank's comments on pokeweed. New on me and I now find out that the thing is native here.
Happily have not met it in the garden. The one, (true/introduced) actual invasive, I've experienced here, is the small tree, buckthorn. A neighbour had one, which produced prolific numbers of berries, brought by birds, to our own garden. One year, I counted up to 350 seedlings as I pulled them out and, though we paid to remove the tree from the neighbour's garden about five years ago, some buckthorn seedlings are still appearing on our side of the fence.
For me, it's one of the trials of gardening: a tree that produces countless numbers of berries, poisonous to mammals, but not only popular with birds, but which produces a mildly laxative effect, in the birds, to speed it's progeny on their way.
Of course, from the environmental side, the fast rate of spread of the introduced buckthorn is a real threat to ecological systems here, including at the edge of woodlands/forests.
