Japanese barberry (berberis thunbergii) is a compact, woody shrub with arching branches. Most commonly it is two or three feet high, but can grow to six feet in height. On the stems, there is a single spine below each rosette of wedge-shaped, untoothed leaves.
The yellow flowers are bisexual, have four sepals (modified leaves below the petals), and the sepals and petals are similar in appearance. The flowers produce small, oblong red berries that are borne singly or in clusters from the stem. The inner bark and roots of Japanese barberry are yellow.
Japanese barberry is found along roadsides, fences, old fields and open woods.
Japanese barberry flowers in May and the fruits hang from the shrubs during the fall and into the winter. In autumn, the leaves of Japanese barberry turn varying shades of orange, red, and crimson. The woody stems of this shrub persist through the winter. Reproduction may be primarily through seeds, although there are reports of resprouting from roots remaining in the ground.
Japanese barberry is native to Asia. Its range in North America extends from Nova Scotia south to North Carolina, and west to Montana.
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Japanese barberry was discovered in the mountains of Japan and sent to St. Petersburg Botanic Gardens by the Russian botanist Carl Maximowicz in 1864. About 1875, seeds from St. Petersburg were received at the Arnold Arboretum in Massachussetts and, from there, introduced to North America. Japanese barberry has been extremely popular for ornamental hedges because of its scarlet fruit, fall leaf color, and ease of cultivation. As its fruits are often eaten by birds, the plant has easily naturalized.
Common barberry (Berberis vulgaris) is another invasive plant that is less common than Japanese barberry in Connecticut. Similar in general appearance to Japanese barberry, common barberry has toothed leaves, and spines that are double- or triple-branched.
Mechanical removal of the plant is recommended because it is effective and minimally intrusive. In early spring, this is one of the first plants to leaf out and can be distinguished easily from other shrubby vegetation. The use of a hoe, weed wrench, or mattock is suggested to uproot the entire bush and associated roots; gloves will help protect hands from the spines. The uprooted shrubs can be piled as cover for small animals. Plants growing in rock piles, which are difficult to dig out, can be treated with the herbicide glyphosate. Because it is a non-selective herbicide, great care must be taken when using it in order not to harm native plants.
Leaves: abovate to spatulate, usually obtuse, entire, narrowed at base to a short petiole, about 1/2" long in whorls or clusters. Leaves of the shoots metamorphosed into simple spines, bearing fascicles of small foliage leaves in their axles. Stems: woody, slender, with straight single spines; yellow wood and inner bark. Flowers: yellow, 1/4" wide, in elongate racemes, contracted umbel-like clusters, or sometimes solitary. Petals six, usually smaller than the sepals and with two glands at the base of each. Fruit: berries ellipsoid, scarlet, 1/2" long.