Japanese Barberry debuted in April (Can you believe we're in October?) while in flower. Here's a different specimen with fruit. This alien bush makes it into the Massachusetts noxious weed list.
This 1920 excerpt from The American City has a differing viewpoint on the issue of invasiveness:
"It is by making use of the occasional horticultural happening, or by deliberate breeding, that our wealth of trees and plants, useful either for their fruit or their beauty, is increased. Japan has added materially to the hardy trees and plants in general use throughout our country. Perhaps one of the most universally useful shrubs from that country is the Japanese barberry (Berberis Thumbergi). It is not only graceful and beautiful, but free from insect troubles, extremely hardy, and disposed to thrive under a great variety of soils and climatic conditions. When in doubt as to what to plant, one can safely plant Japanese barberry."
The Garden Magazine not only echoes the above advice but also clears up misunderstandings that arose over fears of wheat rust:
"The most generally desirable low hedge plant that can be grown in the Northern states is probably the Japanese Barberry. The Common Barberry and the Purple-leafed Barberry might as well be eliminated now as later. The use of these two plants is being decried and even prohibited in many Western states because of their tendency to spread the wheat rust. This fault is not shared by the Japanese B. Thunbergii, although many a hedge of this fine plant has been sacrificed by ill-informed gardeners who did not realize that the Japanese Barberry was not the undesirable citizens."
Grant, Arthur Hastings; Buttenheim, Harold Sinley. The American City. Volume XXIII. New York, October 1920. 459. Web. Google Book Search. 30 Sep 2009.
Farrington, E. I. The Garden Magazine: Revising Our List of Hardy Shrubs. New York, 1919. 222. Web. Google Book Search. 30 Sep 2009.