Thunb. 1784 not Raf. 1836
Acer palmatum, commonly known as red emperor maple, palmate maple, Japanese maple or smooth Japanese-maple (Japanese: irohamomiji, イロハモミジ, or momiji, 紅葉), is a species of woody plant native to Japan, Korea, China, eastern Mongolia, and southeast Russia. Many different cultivars of this maple have been selected and they are grown worldwide for their large variety of attractive forms, leaf shapes, and spectacular colors.
Acer palmatum is a deciduous shrub or small tree reaching heights of 6 to 10 m (20 to 33 ft), rarely 16 metres (52 ft), often growing as an understory plant in shady woodlands. It may have multiple trunks joining close to the ground. In habit, its canopy often takes on a dome-like form, especially when mature. The leaves are 4–12 cm (1 1⁄2–4 3⁄4 in) long and wide, palmately lobed with five, seven, or nine acutely pointed lobes. The flowers are produced in small cymes, the individual flowers with five red or purple sepals and five whitish petals. The fruit is a pair of winged samaras, each samara 2–3 cm (3⁄4–1 1⁄4 in) long with a 6–8 mm (1⁄4–5⁄16 in) seed. The seeds of Acer palmatum and similar species require stratification in order to germinate.
Even in nature, Acer palmatum displays considerable genetic variation, with seedlings from the same parent tree typically showing differences in such traits as leaf size, shape, and color. Overall form of the tree can vary from upright to weeping.
- Acer palmatum subsp. palmatum. Leaves small, 4–7 cm (1 1⁄2–2 3⁄4 in) wide, with five or seven lobes and double-serrate margins; seed wings 10–15 mm (3⁄8–5⁄8 in). Lower altitudes throughout central and southern Japan (not Hokkaido).
- Acer palmatum subsp. amoenum (Carrière) H.Hara. Leaves larger, 6–12 cm (2 1⁄4–4 3⁄4 in) wide, with seven or nine lobes and single-serrate margins; seed wings 20–25 mm (3⁄4–1 in). Higher altitudes throughout Japan and South Korea.
- Acer palmatum subsp. matsumurae Koidz. Leaves larger, 6–12 cm (2 1⁄4–4 3⁄4 in) wide, with seven (rarely five or nine) lobes and double-serrate margins; seed wings 15–25 mm (5⁄8–1 in). Higher altitudes throughout Japan.
Cultivation and uses
When Swedish doctor-botanist Carl Peter Thunberg traveled in Japan late in the eighteenth century, he secreted out drawings of a small tree that would eventually become synonymous with the high art of oriental gardens. He gave it the species name palmatum after the hand-like shape of its leaves, similar to the centuries-old Japanese names kaede and momiji, references to the 'hands' of frogs and babies, respectively.
Japanese horticulturalists have long developed cultivars from maples found in Japan and nearby Korea and China. They are a popular choice for bonsai enthusiasts and have long been a subject in art.
Preparations from the branches and leaves are used as a treatment in traditional Chinese medicine.
Acer palmatum includes hundreds of named cultivars with a variety forms, colors, leaf types, sizes, and preferred growing conditions. Heights of mature specimens range from 0.5 to 25 m (1 1⁄2 to 82 ft), depending on type. Some tolerate sun, but most prefer part shade, especially in hotter climates. Almost all are adaptable and blend well with companion plants. The trees are particularly suitable for borders and ornamental paths because the root systems are compact and not invasive. Many varieties of Acer palmatum are successfully grown in containers. Trees are prone to die during periods of drought and prefer consistent water conditions; more established trees are less prone to drought. Trees should be mulched with a thick layer of bark. Well-drained soil is essential as they will not survive in soggy waterlogged soil. Trees do not require or appreciate heavy fertilization and should only be lightly fertilized, preferably using slow-release fertilizer with a 3 to 1 ratio of nitrogen to phosphorus respectively. Nitrogen lawn fertilizer should be avoided in the immediate vicinity of these trees as excessive nitrogen can cause overly vigorous growth that is prone to pathogens.
If space is not a constraint, no pruning is necessary except to remove any dead branches. Trees naturally self-prune foliage that doesn't receive enough light, such as internal branches which are overly shaded by its own canopy. Some growers prefer to shape their trees artistically or to thin out interior branches to better expose the graceful main branches. The form of the tree, especially without leaves in winter, can be of great interest and can be pruned to highlight this feature. Trees heal readily after pruning without needing aftercare. This species should not be pruned like a hedge, but instead methodically shaped by carefully choosing individual branches to remove. They can also be pruned just to maintain a smaller size to suit a particular location. Acer palmatum can also be used as espalier.
Over 1,000 cultivars have been chosen for particular characteristics, which are propagated by asexual reproduction most often by grafting, but some cultivars can also be propagated by budding, cuttings, tissue culture, or layering. Some cultivars are not in cultivation in the Western world or have been lost over the generations, but many new cultivars are developed each decade. Cultivars are chosen for phenotypical aspects such as leaf shape and size (shallowly to deeply lobed, some also palmately compound), leaf color (ranging from chartreuse through dark green or from red to dark purple, others variegated with various patterns of white and pink), bark texture and color, and growth pattern. Most cultivars are less vigorous and smaller than is typical for the species, but are more interesting than the relatively mundane species. Cultivars come in a large variety of forms including upright, broom, weeping, cascading, dwarf, and shrub. Most cultivars are artificially selected from seedlings of open-pollinated plants, purposeful breeding is not common, and less often from grafts of witch's brooms.
In Japan, iromomiji is used as an accent tree in Japanese gardens, providing gentle shade next to the house in the summer and beautiful colors in autumn. Many cultivars have characteristics that come into prominence during different seasons, including the color of new or mature leaves, extraordinary autumn color, color and shape of samaras, or even bark that becomes more brightly colored during the winter. Some cultivars can scarcely be distinguished from others unless labeled. In some cases, identical cultivars go by different names, while in other cases, different cultivars may be given the same name.
A selection of notable or popular cultivars, with brief notes about characteristics that apply during at least one season, includes the following. agm indicates the cultivar has gained the Royal Horticultural Society's Award of Garden Merit.
- 'Aka shigitatsu sawa'; pinkish-white leaves with green veins
- 'Ao ba jo'; a dwarf with bronze-green summer foliage
- 'Atropurpureum'; wine-red, including new branches (see 'Dissectum Atropurpureum')
- 'Bloodgood'agm; an improved cultivar of 'Atropurpureum'
- 'Burgundy Lace'agm
- 'Butterfly'; small leaves with white borders
- 'Crimson Queen' (see var. dissectum 'Crimson Queen')
- 'Dissectum'; lace-like leaves, drooping habit
- 'Dissectum Atropurpureum'
- var. dissectum 'Crimson Queen'agm
- var. dissectum 'Garnet'agm
- var. dissectum 'Inaba-shidare'agm
- var. dissectum 'Seiryu';agm a green, tree-like shrub with finely dissected leaves
- 'Emperor 1'
- 'Garnet' (see var. dissectum 'Garnet')
- 'Golden Pond'; greenish-yellow summer foliage
- 'Goshiki koto hime'; a delicate, variegated dwarf
- 'Higasa yama'; crinkled leaves variegated with yellow
- 'Hogyuko'; rich green leaves, turning orange in autumn
- 'Hupp's Dwarf'; a small, dense shrub with miniature leaves
- 'Inaba-shidare' (see var. dissectum 'Inaba-shidare')
- 'Issai nishiki kawazu'; very rough, rigid bark
- 'Jerre Schwartz'; dwarf variety, toothed, deeply lobed, mid-dark green leaves, flushed pink and then bronze-green in spring, turning red in autumn.
- 'Kagiri nishiki'; similar to 'Butterfly' but more pinkish tones
- 'Karasu gawa'; slow-growing variegate with brilliant pink and white
- 'Katsura'agm; yellow-green leaves tipped with orange
- 'Koto no ito'; light green, thread-like leaves
- 'Little Princess'; a sparsely branched dwarf with irregular habit
- 'Mama'; a bushy dwarf with extremely variable foliage
- 'Masu murasaki'; a shrubby tree with purple leaves
- 'Mizu kuguri'; orange-tinted new growth and very wide habit
- 'Nigrum';agm deep purple leaves turning to crimson
- 'Nishiki gawa'; pinetree-like bark desirable for bonsai
- 'Nomura nishiki'; dark purple, lace-like leaves
- 'Ojishi'; tiny dwarf, grows only a few centimetres per year
- 'Orange Dream';agm leaves yellow in spring, greenish in summer, orange-yellow in autumn. Bark bright green
- 'Osakazuki';agm tree-like shrub with spectacular autumn colour
- 'Peaches and Cream'; similar to 'Aka shigitatsu sawa'
- 'Pink Filigree'; finely dissected, brownish-pink leaves
- 'Red Filigree Lace'; delicate, finely dissected, dark purple
- 'Red Pygmy'agm
- 'Sango kaku';agm Coral-bark maple (formerly 'Senkaki'); with pinkish-red bark
- 'Seiryu' (see var. dissectum 'Seiryu')
- 'Shaina'; a dwarf sport from 'Bloodgood'
- 'Shikage ori nishiki'; vase-shaped shrub with dull purple foliage
- 'Skeeter's Broom'; derived from a 'Bloodgood' witch's broom
- 'Tamukeyama'; finely dissected, dark purple, cascading habit
- 'Trompenburg';agm slender, upright grower, convex lobes, purple leaves
- 'Tsuma gaki'; yellow leaves with reddish-purple borders
- 'Villa Taranto'agm
- 'Yuba e'; upright tree with scarlet variegation
In addition to the cultivars described above, a number of cultivar groups have been naturally selected over time to such an extent that seedlings often resemble the parent. Many of these are sold under the same name as the cultivars, or even propagated by grafting, so there is often much ambiguity in distinguishing them. In particular, a number of dark-red Acer palmatum are sold with the names ‘Atropurpureum’ and ‘Bloodgood’. Many different cultivars with delicate lace-like foliage are sold under names such as ‘Dissectum’, ‘Filigree’ and ‘Laceleaf’.
The term "Japanese maple" is also sometimes used to describe other species, usually within the series Palmata, that are similar to A. palmatum and native to China, Korea or Japan, including:
- Acer duplicatoserratum (syn. A. palmatum var. pubescens Li)
- Acer japonicum—Downy Japanese maple
- Acer pseudosieboldianum—Korean maple
- Acer shirasawanum—Fullmoon maple
- Acer sieboldianum—Siebold's maple
- Acer buergerianum—Trident maple
Given that these maples are phenotypically variable within each species, and may hybridise with one another, distinguishing between them may be a matter of gradient speciation. In commercial propagation, A. palmatum is often used as rootstock for many of these other species.
- Barstow, M. & Crowley, D. (2017). "Acer palmatum". The IUCN Red List of Threatened Species. International Union for Conservation of Nature and Natural Resources. 2017. e.T193845A2285627. doi:10.2305/IUCN.UK.2017-3.RLTS.T193845A2285627.en. Retrieved 22 May 2018.
- The Plant List, Acer palmatum Thunb.
- English Names for Korean Native Plants (PDF). Pocheon: Korea National Arboretum. 2015. p. 334. ISBN 978-89-97450-98-5. Archived from the original (PDF) on 25 May 2017. Retrieved 25 January 2016 – via Korea Forest Service.
- "Acer palmatum". Natural Resources Conservation Service PLANTS Database. USDA. Retrieved 6 January 2016.
- "BSBI List 2007". Botanical Society of Britain and Ireland. Archived from the original (xls) on 25 January 2015. Retrieved 17 October 2014.
- "Acer palmatum". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 11 December 2017.
- Philips, Roger (1979). Trees of North America and Europe. New York: Random House. ISBN 0-394-50259-0.
- van Gelderen, C.J. & van Gelderen, D.M. (1999). Maples for Gardens: A Color Encyclopedia.
- Rushforth, K. (1999). Trees of Britain and Europe. Collins ISBN 0-00-220013-9.
- "History of Japanese Maples and Value as a Landscaping Tree". Arbor Day Foundation. Archived from the original on 25 April 2010.
- "Etymology of 楓 [Maple]" (in Japanese).
[The word kaede derives from kaeru te "frog hand" and went through the intermediary form kaende]
- D'Cruz, Mark. "Acer palmatum Bonsai Care Guide". Ma-Ke Bonsai. Retrieved 26 November 2010.
- "Acer palmatum Thunb". School of Chinese Medicine database. Hong Kong Baptist University. Archived from the original on 3 March 2016.
- Vertrees, J.D. (1987) Japanese Maples. Timber Press, Inc. ISBN 0-88192-048-7
- "Acer palmatum 'Beni-maiko' (P)". Royal Horticultural Society. Retrieved 29 December 2017.
- "Acer palmatum 'Beni-tsukasa' (P)". Royal Horticultural Society. Retrieved 29 December 2017.
- "RHS Plant Selector - Acer palmatum 'Bloodgood'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Burgundy Lace'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Chitose-Yama'". Retrieved 10 June 2013.
- "Acer palmatum 'Dissectum Atropurpureum' (D)". Royal Horticultural Society. Retrieved 24 May 2018.
- "RHS Plant Selector - Acer palmatum var. dissectum 'Crimson Queen'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum var. dissectum 'Garnet'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum var. dissectum 'Inaba-shidare'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Seiryu'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Katsura'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Nigrum'". Retrieved 10 June 2013.
- "Acer palmatum 'Orange Dream' (P)". Royal Horticultural Society. Retrieved 6 April 2017.
- "Acer palmatum 'Ornatum' (D)". Royal Horticultural Society. Retrieved 29 December 2017.
- "RHS Plant Selector - Acer palmatum 'Osakazuki'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Red Pygmy'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Sango-kaku'". Retrieved 10 June 2013.
- "RHS Plant Selector - Acer palmatum 'Trompenburg'". Retrieved 10 June 2013.
- "Acer palmatum 'Villa Taranto' (L)". Royal Horticultural Society. Retrieved 29 December 2017.
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