Japanese laurel (Aucuba japonica, Thunb. 1783)

Identity

Japanese laurel (Aucuba japonica Thunb., 1783), also called spotted laurel, Japanese aucuba or gold dust plant, is a dioecious evergreen shrub in the Garryaceae family. Carl Peter Thunberg Latinized the Japanese word aokiba as the genus name when he described the species in 1783. The epithet japonica refers to Japan. ^{1 7}

Leathery, glossy foliage explains the shared common name “laurel,” but Japanese laurel is unrelated to culinary bay (Laurus nobilis) and cherry laurel (Prunus laurocerasus). Their names overlap; their botanical families do not. ^{4 6}

Recognition

Aucuba japonica develops a dense, rounded mound, usually 1.5–3 m (5–10 ft) high, exceptionally 4 m (13 ft) in old specimens. Opposite, leathery, glossy leaves are elliptic to lance-shaped, 8–20 cm (3–8 in) long, with coarse teeth on the upper half. Wild-type foliage is plain green; garden cultivars often have yellow speckles. ^{3 7}

Male and female flowers grow on separate plants. Each small purplish-brown flower has four petals. In Northern Hemisphere gardens they open in March–April, in upright panicles on males and shorter clusters in the leaf axils on females. An ordinary plant bears flowers of only one sex. ^{2 4}

Bright red, egg-shaped drupes offer a particularly useful clue: they measure about 1–1.5 cm (0.4–0.6 in) and develop only on pollinated female plants, often lasting through winter into the next spring. Missing berries can simply mean the shrub is male or lacks a pollination partner. ^{7 4}

Useful taxonomy

Botanists formerly placed Japanese laurel in Cornaceae, then in its own family Aucubaceae. Its current placement is in Garryaceae, order Garryales. These historical changes explain older gardening references to Aucubaceae without altering identification of the living shrub. ^{1 8}

Botanical varieties and forms described under these names include:

• Aucuba japonica var. borealis Miyabe & Kudô, a botanical variety
• Aucuba japonica var. japonica, the typical variety
• Aucuba japonica f. variegata (Dombrain) Rehder, a variegated form
• Aucuba himalaica Hook.f. & Thomson, a related botanical name

Cultivar names such as Crotonifolia and Golden King describe horticultural selections rather than the botanical ranks listed above. Aucuba japonica remains the accepted scientific name to use when checking identity. ^{1 2}

Habitat and range

Moist East Asian woodland is its native setting: southeastern China, Taiwan, Korea and Japan. The shrub occupies rich, damp forest understories, ravines, thickets and shaded stream banks. ^{1 3}

John Graeffer brought a single variegated female plant to England in 1783. Without a male, this lineage failed to fruit for almost eighty years. Imports by Robert Fortune and other collectors in the 1850s–1860s finally brought a male to England; nurseryman Standish displayed the first fruiting in 1864. ⁷

European and North American gardens have since grown the shrub widely. It sometimes naturalizes in mild oceanic climates, but is not reported as invasive in France, where it remains a garden plant; that assessment concerns France specifically. ^{9 2}

Life cycle and reproduction

Separate sexes determine ordinary Japanese laurel fruiting: a female needs pollen from a nearby male to produce berries. An isolated plant without a partner will not fruit simply because it grows older or receives better care. Self-fertile cultivars are an exception, described below. ^{7 2}

Spring flowers rely on insects to carry pollen between nearby male and female shrubs. Flowering falls in March–April in the Northern Hemisphere regions described by the sources. Berries ripen in fall and often persist through winter, being relatively unappealing to local wildlife. ^{4 2}

Semi-ripe stem cuttings provide the most reliable propagation method. The source describes September–February in its Northern Hemisphere context: even a small piece of shoot roots readily without special treatment. Layering also works, but takes about twelve months before the new plant can be separated. ^{5 7}

Uses and risks

Late Victorian England made this ornamental shrub a suburban garden staple. It endured coal smoke and the shade of large trees, and London street vendors sold it in pots. ^{7 2}

Dark borders and shaded back-of-garden hedges still benefit from its dense structure. In cold climates it can also grow in a sheltered container. Tolerance of alkaline soil, clay and sand makes it useful where few other shrubs thrive. ^{5 3}

Iridoid glycosides, aucuboside and aucubin, occur throughout the plant and are concentrated in the berries. A French poison center recorded 78 berry ingestions compared with two leaf ingestions in its study period. Eating the berries most often causes nausea, vomiting and digestive pain, generally without serious effects beyond these common symptoms. ^{6 4}

Varieties, look-alikes and related plants

Garden selections differ chiefly in sex and variegation. Crotonifolia has large golden splashes and is female and fruiting; similarly marked Golden King is male, so supplies pollen but no berries. Rozannie is a self-fertile female that can fruit alone. Salicifolia has narrow, entirely green leaves without variegation. ²

Three plants commonly cause identification mistakes:

• Prunus laurocerasus, cherry laurel, has bitter-almond-scented leaves and much greater cyanogenic toxicity;
• Laurus nobilis, culinary bay, is botanically unrelated despite the shared name;
• Skimmia japonica is another dioecious woodland shrub with red berries, but belongs to Rutaceae.

Odorless leaves, normally separate male and female plants, and exceptional tolerance of deep shade help distinguish Japanese laurel from these look-alikes. ^{4 1}

Main sources

• Plants of the World Online / Kew, Aucuba japonica Thunb.
• Royal Horticultural Society, Aucuba japonica - Japanese laurel
• Missouri Botanical Garden, Aucuba japonica
• North Carolina State Extension, Aucuba japonica
• Plants For A Future, Aucuba japonica
• Lille Poison Control Center, Aucuba: a plant with poisonous berries
• Trees and Shrubs Online (Bean's), Aucuba japonica
• International Plant Names Index, Aucuba japonica Thunb.
• USDA PLANTS Database, Aucuba japonica Thunb.