Zelkova serrata (Japanese zelkova,Japanese elm,^[2]keyaki, orkeaki;Japanese:欅 (ケヤキ) keyaki /槻 (ツキ) tsuki;Chinese:榉树/櫸樹 jǔshù;Korean:느티나무 neutinamu) is aspecies of the genusZelkovanative toJapan,Korea, easternChina andTaiwan.^[3][4] It is often grown as anornamental tree, and used inbonsai. There are twovarieties,Zelkova serrata var.serrata in Japan and mainland eastern Asia, andZelkova serrata var.tarokoensis (Hayata) Li on Taiwan which differs from the type in its smaller leaves with less deeply cut serration on the margins.^[4]

Zelkova serrata
"Noma Keyaki", a 1,000-year-old keyaki inNose nearOsaka inJapan, 25 m tall, 11.95 m trunk circumference; second-largest known specimen[1]
Conservation status
Near Threatened (IUCN 3.1)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Rosids
Order:	Rosales
Family:	Ulmaceae
Genus:	Zelkova
Species:	Z. serrata
Binomial name
Zelkova serrata (Thunb.)Makino

Zelkova serrata is a medium-sizeddeciduous tree usually growing to 30 m (98 ft) tall. It is characterized by a short trunk dividing into many upright and erect spreading stems forming a broad, round-topped head. The tree grows rapidly when young though the growth rate slows to medium upon middle age and maturity.^[5]

It has alternately arranged leaves growing to 5 cm (2 in) long and broad. The leaves themselves are simple andovate to oblong-ovate with serrated or crenate margins, to which the tree owes itsspecific epithetserrata. The leaves areacuminate orapiculate, rounded orsubcordate at the base, and contain 8–14 pairs of veins. The leaves are rough on top andglabrous or nearly glabrous on the underside. They are green to dark green in spring and throughout the summer, changing to yellows, oranges and reds in autumn. Thepetioles are 2–5 mm (1⁄16–3⁄16 in) long.^[6]

Zelkova serrata ismonoecious. It develops flowers in spring with the leaves. Buds are ovoid, acutish, with manyimbricate, dark brown scales.^[5] They diverge at a 45-degree angle from the stem. Thestaminate flowers are shortlypedicellate and approximately 3mm in diameter, clustered in theaxils of the lower leaves. Thepistillate flowers are solitary or few in axils of the upper leaves,sessile and usually about 1.5 mm in diameter. The flowers are yellow-green, not showy, and occur in tight groups along new stems. They give rise to small, ovate, winglessdrupes that ripen in late summer to autumn. The drupe is green maturing to brown, subsessile and2.5 to 3.5 mm (3⁄32 to1⁄8 in) in diameter.

To identifyZelkova serrata, one would look for a short main trunk, low branching and a vase-shaped habit. The twigs are slender with small, dark conical buds in a zigzag pattern. The branches are usually glabrous. The bark is grayish white to grayish brown and either smooth withlenticels or exfoliating in patches to reveal orange inner bark. The branchlets are brownish-purple to brown.

The threats to this tree include colder temperature, which often result in twig dieback. It is highly resistant toDutch elm disease, which makes it a good replacement tree for American elm.Zelkova serrata is similar in appearance to the elms, though may be distinguished by its unwinged fruit and leaves which are symmetrical rather than uneven at their base.^[7]Zelkova serrata also shows good resistance toelm leaf beetle andJapanese beetle.^{[citation needed]}

The tree is prone to fungusGriphosphaerioma zelkovicola which was first observed in Japan on the bark ofZelkova serrata trees in 2003.^[8]

Zelkova serrata is planted as a lawn or park tree for its attractive bark, leaf color and vase shape. It provides good shade and has an easy fall cleanup. It is easy to transport, and often available in burlap form. It is also commonly used forbonsai; its attractive shape and colors make it a popular choice for the art.^[3][4] It is often grown as anornamental tree, both in its native area and in Europe and North America. The first cultivation outside of Asia was byPhilipp Franz von Siebold, who introduced it to theNetherlands in 1830.^[4] Recently, it has been planted as a "street tree" in New York City^[9] and Philadelphia. In the UK it has gained theRoyal Horticultural Society'sAward of Garden Merit.^[10]

Within the United Kingdom, the Royal Horticultural Society's Plantfinder currently lists 38 suppliers for the pure species and associated varieties.^[11]

This tree requires full to partial sun and prefers moist, well-drained soils. A fertilizer rich in potassium and nitrogen encourages new vegetation and floral buds. It is adaptable and tolerant of heat, little water, nutrient-poor soils and various pH. It should be periodically thinned to allow light into the inner canopy.Zelkova Serrata is propagated by seeds, rooted stem cuttings and grafting. The seeds germinate without pretreatment, though the percentage is better when stratified at 5 °C (41 °F) for 60 days.^[5] Because germination requires stratification, the seed is best sown early in the year. To ensure survival it may be necessary to pot the tree and grow it in a greenhouse for its first winter. It may be reintroduced into its permanent habitat after the final frost.^{[citation needed]}

Numerouscultivars have been selected, including:

It has alsohybridised withZelkova carpinifolia in Europe, the hybrid being namedZelkova ×verschaffeltii.^[4]

Keyaki wood is valued in Japan and used often for furniture, such astansu, as well as being considered the ideal wood for the creation oftaiko drums.

In Korea,Zelkova serrata has been considered a symbol of protection for villages since ancient times, and can still be found planted at central points in cities, towns and villages around the country.^[13] The trees often stand next to small pavilions, serving both as shaded informal gathering points, and spaces for traditional rituals and ceremonies involving prayer and offerings to the tree.^[14] The oldest of these trees are estimated to be in excess of 1,000 years in age, and are protected as natural monuments by Korean law.^[15] In 2013, the Korea Forest Research Institute announced a project to clone the zelkova,pine, andginkgo trees that are identified as natural monuments, so their lineage will not be lost in case of disaster or death due to age.^[16]

According to data investigated byKorea Forest Service in 1989, the largest number of trees over 500 years old were specimens ofZelkova serrata, among which more than ten have been registered as Natural Monuments of Korea.^[17]

The tree is a symbol of a number of Japanese cities and prefectures:Saitama Prefecture, Miyagi Prefecture, Fukushima Prefecture, Fukushima-shi, Abiko-shi, Tachikawa-shi, Yokohama-shi,Machida City inTokyo Metropolis District,Takatsuki City and more.

•  
  Autumn colour, November, Saitama Prefecture, Japan
•  
  Trees lining an avenue in Sendai, Japan
•  
  Morton Arboretum
  acc. 10-54-1
•  
  A Japanese Sendai-dansu for kimono made from keyaki wood
•  
  Sasayama,Hyogo in the winter
•  
  An example of a mature tree

• "Zelkova Serrata." The Ohio State University. 4 May 2009.