A deciduous shrub, of very close, compact habit, from 3 to 8 ft high, with stiff, deeply grooved branches, and glabrous, reddish-brown bark. Leaves crowded in tufts along the branches (the tufts often 1⁄4 to 1⁄2 in. apart), obovate or spathulate, 1⁄2 to 11⁄4 in. long, sometimes rounded at the apex, sometimes spine-tipped, never toothed. The thorns on the branches are about 1⁄2 in. long, almost invariably single, but occasionally three-pronged. Flowers 1⁄3 to 1⁄2 in. across, usually solitary in each tuft of leaves, but sometimes in pairs, each one borne on a slender stalk 1⁄2 in. long; sepals small, dull red; petals twice as long, pale yellow suffused with red. Berries bright red, 1⁄3 in. long. Bot. Mag., t. 6646.
The first European to notice this barberry was Thunberg, who saw it in Japan in 1784, but it did not reach this country until about ninety years later. It has been found wild in China. Latterly it has become popular in gardens, owing to its neat, close habit, its handsome red fruits, but more than all for its brilliant red foliage in autumn. The flowers, although unusual in colour and freely borne, are not showy. In the suburbs of Boston, Mass., in the neighbourhood of the Arnold Arboretum, it thrives remarkably; I have measured bushes there 8 ft high and 15 ft across.
f. atropurpurea (Chenault) Rehd. – Summer foliage in some shade of purplish or reddish brown. The original plant arose in the nursery of Messrs Renault (not Chenault) of Orleans around 1913 but was not distributed until about 1926. The raisers at first propagated this barberry vegetatively but later used seeds, by which means it seems to have been propagated ever since (Krüssmann in Die Deutsche Baumschule, Vol. 5, p. 143).
cv. 'Atropurpurea Nana'. – A bush with brownish red leaves, growing to about 2 ft high, raised by Messrs Van Eyck, Boskoop, Holland, 1942. A useful shrub for massing, which assorts well with heaths. It is a clone, and is also known as “Little Favourite”.
var. maximowiczii (Reg.) Reg. B. maximowiczii Reg. – Branches more twiggy, with a purple bark. Leaves more purple, green beneath. The form distributed by Messrs Marchant has orange-red and yellow autumn colour.
cv. 'Minor'. – A form of dwarf habit, with smaller leaves and flowers, which arose as a seedling in the Arnold Arboretum. Also known as B. t. dawsonii.
cv. 'Rose Glow'. – Leaves purple, variegated pink and white. Raised by Messrs Spaargaren and Sons, Holland, around 1957 and introduced to this country in 1965.
In the United States, where B. thunbergii is more valued than it is here, a seed strain has been developed by Messrs Horvath of Mentor, Ohio, which is upright and intended for hedging (D. Wyman, Shrubs and Vines for American Gardens, 1961). It is known as B. t. erecta. The same firm has produced a very hardy hybrid between B. thunbergii and B.julianae, marketed as B. mentorensis.
From the Supplement (Vol. V)
This species is unusual among the deciduous kinds in being fairly easily raised from cuttings, and in being very productive of cultivars. Mention is made below of some that have been introduced to Britain in the past fifteen years or so, all raised in Holland unless otherwise stated.
† cv. 'Aurea'. – Leaves bright yellow, tending to become yellowish green in late summer, and also burning in full sun. Raised in the USA and introduced to Britain late in the 1960s. The form in commerce is low-growing and compact, but it is doubtful whether the name is really clonal.
f. atropurpurea – There are now numerous selections in this group, such as 'Helmond Pillar' and 'Red Pillar', both of narrowly erect habit; 'Red Chief', vigorous and of graceful habit, to about 7 ft high; and 'Dart's Red Lady', of spreading habit, with dark purple leaves, colouring well in autumn.
cv. 'Atropurpurea Nana'. – Possible improvements on this are 'Dart's Purple', similar in habit but with brighter coloured foliage; and 'Bagatelle', very dwarf and slow growing, of rounded habit.
cv. 'Golden Ring'. – Leaves purple, large, with a gold rim. The name is not strictly clonal, as several similar seedlings were propagated and sent out under it (Dendroflora, No. 9 (1972), p. 32). A similar plant is sold in Britain as 'Gold Rim'.
† cv. 'Green Ornament'. – A fairly vigorous green-leaved selection, with ascending branches; free-fruiting. 'Green Carpet' is spreading, to 2 ft or so high.
cv. 'Minor'. – A similar and perhaps better clone is 'Kobold', which grows to about 11⁄2 ft high.
cv. 'Rose Glow'. – Said to be an improvement is 'Pink Queen', with a light pink instead of a white variegation.
† B. 'Parkjuwel'. – A hybrid between B. thunbergii (seed parent) and some evergreen barberry, either B. candidula or B. × hybrido-gagnepainii. It is a dense shrub of roundish habit to about 4 ft high, with almost entire leaves which mostly persist through the winter. Its flowers are of little account. When describing it in 1956, H. J. Grootendorst gave it botanical status as B. × media 'Parkjuwel'. 'Red Jewel' is a sport from this, with red-bronze young foliage.