Flower:

One to 5 dangling, stalked flowers at the tips of short lateral branchlets all along 1-year-old branches. Flowers are pale yellow, ¼ to 1/3 inch across when fully open and have 6 petals. At the base of each petal is a single stamen; in the center is a green, flat-topped ovary.

Surrounding the base of the flower are 6 petal-like sepals as long as the petals and 3 greenish-yellow bracts that are shorter, all dropping off with the petals soon after pollination. Flower stalks, sepals and bracts are all hairless.

Leaves and stems:

Leaves are clustered at branchlet tips, alternate but appearing whorled, up to about 1 inch long and 3/8 inch wide, toothless, hairless, mostly spatula-shaped, blunt to rounded at the tip, tapering at the base to a short stalk. The lower surface may have a waxy coating (glaucous). Color is typically bright green turning orange, red or dark purple in fall.

New twigs are hairless, yellowish or purplish becoming ridged and purplish-brown the second year. At the base of each branchlet is usually a single spine; occasionally spines are 3-pronged. Older bark is gray and rough. Stems are erect to ascending, multiple from the base, many-branched with the branches long, slender, often arching, and spreading in all directions like tentacles. Branches that touch the ground can reroot; new shoots also emerge from root suckers as well as root fragments.

Fruit:

Fruit is a bright red, oval-elliptic berry, about 3/8 inch (1 cm) long, containing a few seeds and persisting through winter.

Notes:

Japanese Barberry was introduced to North America in 1875 and had naturalized in the wild by the early 1900s. It has long been marketed as an ornamental in the garden trade with numerous cultivars available, sporting a wide range of leaf colors and in forms from compact mounds to 5-foot hedges. It easily escapes cultivation, commonly spread by birds that eat the fruit and then taking off on its own by seed and vegetatively, and is considered invasive pretty much everywhere it is found in North America. Pouring salt into that wound, research has shown that areas infested with Japanese Barberry also have a higher risk of Lyme disease-carrying ticks. It is also an alternative host for black stem rust, which can devastated wheat crops. Bad plant all around. Canada saw fit to ban it in 1966 but the US saw fit to make money from its sale instead.

In Minnesota, it was added to the Restricted Noxious Weed list in 2017, which means it's been recognized as a pest plant but is too widely established for effective control, let alone eradication, so all the powers-that-be can do now is prohibit its further sale, propagation, or transport within the state. Note that about 25 named cultivars and hybrids as well as the wild type are listed (but are there others not listed?). In any case, like many invasive species this is too little too late—that horse is already out of the barn. Perhaps a biological control agent will be discovered some day but none exists now. The herbarium records don't show the real spread of this species in Minnesota; reports at EDDMapS, a national weed-mapping system, show it is much more widespread throughout the state.

Japanese Barberry is easily recognized by its numerous, often arching, tentacle-like branches with clusters of spatula-shaped leaves on short, lateral branchlets. The leaves are only about 1 inch long and toothless, and there is usually a single spine at the base of a branchlet. Stalked flowers and fruits are dangling in groups of 1 to 5 from branchlet tips. The only other Barberry (native or not) recorded in Minnesota is Common Barberry (Berberis vulgaris), which is less widely spread, has toothed leaves and spines are usually 3-pronged.