Native fruit tree genetic resources in Japan

Abstract

The diversity of climate, from subarctic to subtropical, and the complex geological history of Japan have produced a rich biodiversity. The flora includes several hundred species of native woody plants with edible fleshy fruits or nuts. People have eaten them from prehistoric times until about a half century ago. In Hokkaidō and the Ryūkyū Islands nut species had an important role in the diet, but fleshy fruits were also eaten until recently. Only Castanea crenata and a few minor species became domesticated as edible fruit trees in pre-modern times. Recently, Vitis coignetiae, Lonicera caerulea, Akebia quinata, Akebia trifoliata, Stauntonia hexaphylla, and Actinidia arguta have entered small-scale cultivation. The conservation of the germplasm of many of these native species, both in situ and ex situ, is precarious.

Introduction

Biodiversity in Japan

The Japanese archipelago is located on the east coast of the Asian continent. The diversity of its climate, from subarctic to subtropical, with high humidity and precipitation throughout has produced a rich biodiversity (Iwatsuki et al. 1993–2016, Ohwi 1965). The connection with the continent several times before the last glacial maximum may have promoted migration from north and south to produce a flora with mixed subarctic, temperate, and subtropical elements. By contrast, its isolation after the last glacial maximum may have stimulated the phylogenetic differentiation of taxa from the continental mother taxa. However, this biodiversity hotspot (Mittermeier et al. 2004) is also one of the most populous regions in the world. The population pressure poses threats to wild ecosystems both directly via exploitation and indirectly via environmental degradation. More than 2000 species of flora are now threatened (Ministry of Environment of Japan 2012).

Definition of Japanese native fruit trees in this review

Japan has about 5000 species of seed plants (Kajita 2003). About 1000 species are woody, either trees, shrubs, or vines (Satake et al. 1989), and these include many fleshy fruit and nut species. In addition, some species were introduced in the Middle Ages or before. Formerly, some commercial fruit species, including Pyrus pyrifolia (Burm. f.) Nakai and Amygdalus persica L. (=Prunus persica (L.) Batsch), were thought to have originated from native plants (e.g., Kikuchi 1948). Now they are considered to have been introduced in pre-modern times (“archaeophytes”), though empirical confirmation is still rare (e.g., Iketani et al. 2010a, 2012). These introduced plants (listed in Table 1) are excluded from subsequent treatment in this review.

Table 1 Fruit trees introduced to Japan in pre-modern times

Species	Period of Introduction	Literature1 (introduced)	Literature1 (native)
Gingko biloba L.	13–14th Century	Hori and Hori (1997)
Ficus carica L.	17th Century?	Kikuchi (1948)
Eriobotrya japonica (Thunb.) Lindl.	Prehistoric	Kobayashi (1990)	Kikuchi (1948)
Malus asiatica Nakai	12th Century? 14–15th Century	Kitamura (1979) Kobayashi (1990)
Armeniaca vulgaris Lam. (Prunus armeniaca L.)	Prehistoric	Kikuchi (1948), Kobayashi (1990)
Armeniaca mume (Siebold et Zucc.) de Vriese (Prunus mume Siebold et Zucc.)	Prehistoric	Kitamura (1979) Kobayashi (1990)	Kikuchi (1948)
Prunus salicina Lindl.	Prehistoric	Kitamura (1979) Kobayashi (1990)	Kikuchi (1948)
Amygdalus persica L. (Prunus persica (L.) Batsch.	Prehistoric	Kitamura (1979) Kobayashi (1990)	Kikuchi (1948)
Pyrus pyrifolia (Burm.f.) Nakai	Prehistoric	Kobayashi (1990)	Kikuchi (1948)
Diospyros kaki Thunb.	Prehistoric	Kobayashi (1990)	Kikuchi (1948)
Vitis vinifera L.	7th Century?	Kobayashi (1990)
Ziziphus jujuba Mill.	6–7th Century	Kobayashi (1990)
Citrus spp.	6–7th Century	Kobayashi (1990)
Punica granatum L.	12th Century?	Kikuchi (1948)

¹  Literature supporting the hypothesed origin.

In a broad sense, all non-poisonous fleshy fruits and nuts are edible, and people might have eaten them, especially during times of famine. However, this review covers only plants that were eaten regularly. It excludes plants used only as folk medicine or to produce fruit liquor.

This review covers species supported by archeological evidence (e.g., Terasawa and Terasawa 1981), old historical documents (e.g., Fujiwara et al. 927), or ethnological information (e.g., Sarashina and Sarashina 1976); species that are now commercially grown or marketed even at a minor scale; and species with edible congeners in other regions of the world. In all, 70 genera are included (Table 2).

Table 2 List of Japanese native fruit and nut species. The arrangement of families and scientific names follows Yonekura (2012)

Family	Genus	Edible part1	Growth Form2	Life Form3	Vegetation Zone4	Floristic Region5	Beginning of Cultivation6	Congeneric cultivated species7	Number of species8	Number of threatened taxon9	Representative (possibly) utilized species	Literature10
Cycadaceae	Cycas	N	S	E	ST	A, Oc			1		C. revolta Thunb.	Sa, Ta
Pinaceae	Pinus	N	S, T	E	Sa-ST	N		+	7	1	P. koraiensis Siebold et Zucc.
Cephalotaxaceae	Cephalotaxus	N	S, T	E	Tm-W	EA			8		C. harringtonia (Knight ex Forbes) K.Koch	W
Taxaceae	Torreya	N	S, T	E	Tm-W	W			1		T. nucifera (L.) Siebold et Zucc.	T, W
Laulaceae	Cinamomum	F	S, T	E	ST, T	A			7	2	C. yabunikkei H.Ohba	Sa
	Litsea	F	S, T	E	W-T	A			9	1	L. coreana H.Lév.	Sa
Pandanaceae	Pandanus	F	T	E	ST	OW		+	1	1	P. odoratissumus L.f.	Am, Om, Ta, Sa
Lardizabalaceae	Akebia	F	V	D	Tm-W	EA	R		2		A. quinata (Houtt.) Decne., A. trifoliata (Thunb.) Koidz.	F, Ma
	Stauntonia	F	V	E	W	EA	R		1		S. hexaphylla (Thunb.) Decne.	F
Grossulariaceae	Ribes	F	S	D	Tm	N		+	9	3	R. japonicum Maxim., R. latifolium Janz.	Ma, S
Vitaceae	Ampelopsis	F	V	D, E	Tm-W	AA			4		A. glandulosa (Wall.) Momiy.	W
	Vitis	F	V	D	Tm-ST	N	R	+	5	2	V. coignetiae Pulliat ez Planch, V. flexuosa Thunb.	Hk, Om, S, T, Ta
Rosaceae	Amelanchier	F	S, T	D	Tm	N		+	1		A. asiatica (Siebold et Zucc.) Endl. ex Walp.
	Cerasus	F	T	D	Tm-W	EU		+	10	4	C. jamasakura (Siebold ex Koidz.) H. Ohba
	Cragaegus	F	T	D	Tm	N		+	2	2	C. chlorosarca Maxim.
	Malus	F	T	D	Tm	N		+	5	2	M. toringo (Siebold) Siebold, M. baccata Borkh.	S
	Padus	F	T	D	Tm	N		+	4		P. avium Mill.	Ai
	Pyrus	F	T	D	Tm	EU	O	+	2	2	P. ussuriensis Maxim.	Ma
	Rhaphiolepis	N	S	E	W	EA			1		R. indica (L.) Lindl.	Sa, Ta, W
	Rosa	F	S	D	Tm-W	N	R		12	2	R. rugosa Thunb.	Fu, Hk, S
	Rubus	F	S	D, E	Tm-W	N		+	44	10	R. idaeus L.	F, S, Sa, T, Ta
	Sorbus	F	S, T	D	Tm	N		+	4		S. commixta Hedl.
Elaegnaceae	Elaeagnus	F	S, T, V	D, E	Tm-W	N	R	+	16	5	E. multiflora Thunb.	Ma, S, T, Sa, Ta
Rhamnaceae	Berchemia	F	S, T	D, E	Tm-W	W			5		B. lineata (L.) DC.	Ta
	Sageretia	F	S, T	D, E	W-ST	W			1		S. thea (Osbeck) M.C. Johnst.	Ta
Moraceae	Bloussonetia	F	S, T	D	Tm-W	EA			3		B. papyrifera (L.) l’Hér. ex. Vent.	Om, W
	Ficus	F	S, T	D, E	W-ST	T		+	15	2	F. erecta Thunb.	F, T, Ta, W
	Morus	F	S, T	D	W	AA		+	4	1	M. australis Poir.	Om, Sa
Fagaceae	Castanea	N	T	D	Tm-W	N	O	+	1		C. crenata Siebold et Zucc.	F, Fu, Ht, M, T, W
	Castanopsis	N	T	E	W	EA			2		C. sieboldii (Makino) Hatus. ex T.Yamaz. et Mashiba	Om, M, Ta, W
	Fagus	N	T	D	Tm	N			2		F. crenata Blume	M, W
	Lithocarpus	N	T	E	W-T	AA			2		L. edulis (Makino) Nakai	F, M, Om, Ta, W
	Quercus	N	T	D, E	Tm-W	N			15	1	C. crispa Blume, C. serrata Murray	Fu, Ht, M, Om, S, T, Ta, W
Myricaceae	Myrica	F	T	E	W	N	O	+	2		M. rubra Lour.	Om, Sa, T, Ta, W
Juglandaceae	Juglans	N	T	D	Tm	N		+	1		J. mandshurica Maxim.	Fu, Hk, Ma, M, S, T, W
Betulaceae	Corylus	N	S	D	Tm	N		+	2		C. heterophylla Fisch. ex Besser	F, W
Celastraceae	Euonymus	N	S, T, V	D, E	Tm, W	N			19	6	E. carnosus Hemsl.	Ta
	Gymnosporia	N	S	E	ST-T	W			1	1	G. diversifolia Maxim.	Sa
Elaeocarpaceae	Elaeocarpus	N	T	E	W-T	OW			4	1	E. japonicus Siebold et Zucc.	Om, Ta
Euphobiaceae	Mallotus	N	S, T	D, E	W-T	OW			3		M. japonicus (L.f.) Müll.Arg.	W
Phyllantaceae	Antidesma	F	S, T	E	W-T	OW			4		A. japonicum Siebold et Zucc.	Ta
	Bischofia	F	T	E	ST-T	OW, Oc			1		B. javanica Blume	Sa, Ta
Salicaceae	Idesia	F	T	D	Tm-W	EA			1		I. poplycarpa Maxim.	L, Om, Ta
Calophyllaceae	Calophyllum	F	T	E	ST-T	T			1		C. inophyllum L.	Ta
Combretaceae	Terminalia	N	T	D, E	ST-T	OW, Oc			2		T. catappa L.	Ta
Mytaceae	Syzigium	F	S, T	E	ST-T	A, Oc		+	2		S. buxifolium Hook. et Arn.	Ta
Melastomataceae	Melastoma	F	S	E	ST-T	A, Oc			2	2	M. candidum D.Don	Ta, Sa
Anacardiaceae	Choerospondias	F	T	D	W	EA			1	1	C. axillaris (Roxb.) B.L.Burtt et A.W.Hill	W
Sapindaceae	Aesculus	N	T	D	Tm	N			1		A. turbinata Blume	Ht, M, W
Rutaceae	Phellodendron	F	T	D	Tm	EA			1		P. amurense Rupr.	Fu, Hk
	Toddalia	F	V	W	ST-T	A			1		T. asiatica (L.) Lam.	Ta
Malvaceae	Firmiana	F	T	D	ST-T	OW			1		F. simplex (L.) W.F.Wight	Ta
Santalaceae	Buckleya	N	S	D	Tm-W	AA			1		B. lanceolata (Siebold et Zucc.) Miq.	Ma
Cornaceae	Cornus	F	T	D	Tm-W	N		+	4	2	C. kousa Buerger ex Hance
Sapotaceae	Planchonella	F	S, T	E	ST-T	T			2		P. obovata (R.Br.) Pierre	Ta
Pentaphyllacae	Adinandra	F	S, T	E	ST-T	OW, Oc			2		A. ryukuensis Masam.	Ta
Ebenaceae	Diospyros	F	T	D, E	Tm-ST	T		+	6	2	D. japonica Siebold et Zucc.	Ma, Sa, T, Ta
Primulaceae	Ardisia	F	S, T	E	W-T	T			8	2	A. quinquegona Blume, A. sieboldii Miq.	Ta, Sa
Theaceae	Camellia	N?	S, T	E	W	EA			4		C. japonica L.	Sa, W
Symplocaceae	Symplocos	F	S, T	D, E	Tm-T	T			24	3	S. sp. (undetermined)	Sa
Actinidiaceae	Actinicia	F	V	D, E	Tm-W	EA	R	+	4		A. arguta (Siebold et Zucc.) Planch. ex Miq, A. polygama (Siebold et Zucc.) Planch. ex Maxim., A. rufa (Siebold et Zucc.) Planch. ex Miq.	Fu, Hk, Om, S, Ta, W
	Sauraria	F	S, T	E	ST-T	AA			1		S. tristyla DC.	Ta
Ericaceae	Empetrum	F	S	E	Sa	A			1		E. nigrum L.	Fu, Hk
	Vaccinium	F	S	D, E	Sa-W	N	R	+	19	5	V. oxycoccos L., V. oldhamii Miq, V. uliginosum L.	Hk, S, Sa, Ta
Boraginaceae	Ehretia	F	T, S	D, E	W-T	T			4		E. dicksonii Hance, E. microphylla Lam.	Am, Om, Ta
Oleaceae	Ligustrum	F	S, T	D, E	Tm-W	W			9	1	L. japonicum Thunb.	Sa
Goodeniaceae	Scaevola	F	S, V	E	ST-T	T			1		S. taccada (Gaetrn.) Roxb.	Ta
Adoxaceae	Sambucus	F	S	D	Tm	N		+	2		S. racemosa L.	Ai
	Viburnum	F	S, T	D, E	Tm-T	N			16	3	V. suspensum Lind.	Ma, Sa
Caplifoliaceae	Lonicera	F	S	D	Tm-W	N	R	+	23	14	L. caerulea L.	Ma, S
Total									387	84

¹  F, fleshy part; N, nut.

²  S, shrub; T, tree; V, vine.

³  D, deciduous; E, evergreen.

⁴  Sa, subarctic; Tm, temperate; W, warm temperate; ST, subtropical; T, tropical.

⁵  A, Asian; AA, Asia-American; EA, East Asian; EU, Eurasian; N, Northern Hemisphere; OW, Old world; Oc, Oceanian; T, Tropical; W, Worldwide.

⁶  O, Old (pre-modern); R, Recently (after World War II).

⁷  Presence of congeneric edible cultivated species in other countries.

⁸  Number of species in the genus native to Japan (Yonekura 2012).

⁹  Ministry of Environment of Japan (2012).

¹⁰  Ai, Ainu Museum (2015); Am, Amano (1982); F, Fujiwara et al. (927); Fu, Fukuoka (1995); Hk, Hokkaido Institute of Public Health (2015); Ht, Hatakeyama (1989); L, Liu (1988); Ma, Matsushima et al. (2013); M, Matsuyama (1982); Om, Omatsu and Tsuji (2001); S, Sarashina and Sarashina (1976); Sa, Sato and Nohara (1997); T, Terasawa and Terasawa (1981);Ta, Tawada (1982); W, Watanabe (1975).

Usage of scientific names and Romanization of Japanese in this review

As this review lists many species unfamiliar to breeding science and horticulture, a simple standard for the usage of scientific names is necessary. The review uses names adopted in Yonekura (2012), which is a thorough compilation of the scientific names of vascular plants in Japan, including recent nomenclatural changes after Iwatsuki et al. (1993–2016), and which is now the de facto standard. Full details, including updates, are available on line (Yonekura and Kajita 2003–).

The scientific name of a taxon may be very long and detailed (e.g., using the ranks of subspecies and variety) owing to recent reclassifications based on the broad species concept. This review uses detailed names only when necessary. Otherwise, a simple binomial combination of genus and species is used for convenience and simplicity.

Romanized transcriptions of Japanese names mostly follow the Library of Congress and American Library Association (2012), with a few exceptions such as proper nouns.

Regional usage of fruits and nuts

Japanese fruit and nut trees grow from the subarctic to the subtropics. The Ainu people, the indigenous inhabitants of subarctic Hokkaidō, ate fruits of Empetrum nigrum L. and Vaccinium oxycoccos L., which grow in both uplands and lowlands. They also ate fruits of Phellodendron amurense Rupr., Malus baccata (L.) Borkh. var. mandshurica (Maxim.) C. K. Schneid., Padus avium Mill. (=Prunus padus L.), Rosa rugosa Thunb., Rubus idaeus L., and Sambucus racemosa L., all of which are distributed in the upper-elevation deciduous forest zone and grow widely in the lowlands of Hokkaidō. Species of Ribes, Malus, Rubus, Lonicera and Vaccinium might have also been eaten.

These plants also grow at high altitudes in temperate Honshū but were rarely or never used there, possibly because their habitats were remote from settlements. One exception is Vaccinium uliginosum L., which grows wild above 1500 m a.s.l. in volcanic desert vegetation on Mount Asama and surrounding areas, where local people gathered wild fruits for decades after World War II (Koike and Miyagawa 1974). This practice is now prohibited, because most of the habitat is protected. Another exception is Pyrus ussuriensis var. ussuriensis in the upper deciduous forest zone in northern Honshū (Iwate Prefecture). Trees introgressed with archaeophytic P. pyrifolia grow wild in this area as well as in cultivation (Iketani et al. 2010a, Katayama and Uematsu 2006). Whether this species began to be used before or after introgression is still unknown. This is discussed in more detail by Katayama (2016) in this issue.

Archaeological studies of the utilization of plants in the subtropical Ryūkyū Islands were limited until recent reports of the remains of seeds or stones of many species (e.g., Omatsu and Tsuji 2001). On the other hand, ethnological studies are abundant (e.g., Amano 1982, Sato and Nohara 1997, Tawada 1982). According to these studies, people may have eaten many tree fruits, especially during times of famine (Table 2).

Nut species have been more generally utilized than fleshy fruit species since the hunting-and-gathering age (Taneishi 2014). The most important reason is that nuts are rich in carbohydrates or fats and are thus highly nutritious. Hatakeyama (1989) estimated that wild nuts might have supplied about one-third of the daily energy intake during winter in mountainous settlements of the Kitakami Mountains, where the harvest of cereal crops had been always insufficient. Another reason is that nut genera such as Quercus and Castanea are usually dominant in vegetation, and people can easily gather nuts in abundance. Although Aesculus species contain saponins and most Quercus species contain tannins, people have used them for food by leaching out these components. Nuts have been utilized in almost all areas from Hokkaidō to the Ryūkyū Islands. The Ainu people used only nuts of Quercus, although Aesculus is common in southern Hokkaidō (Watanabe 1975). People continued to eat wild nuts until the 1940s in some regions (Hatakeyama 1989, in the Kitakami Mountains; Sato and Nohara 1997, in the Ryūkyū Islands).

Large seeds of some non-amentiferous species such as Terminalia and Euonymus have been used in the Ryūkyū Islands but their dietary use is almost unknown in mainland Japan (Table 2). It is perhaps because they commonly grow in that Islands. Other large-seeded species in addition to the Fagaceae, Juglans, and Aesculus may also have been eaten in Honshū and Hokkaidō if thinking the high dietary value of seeds.

Domestication of Japanese native wild fruit trees

Domestication in pre-modern times

Humans arrived in Japan around 35 000 years BP or later (Hudson 2007, Keally 2009). During the hunting-and-gathering age, people gathered and ate native fruits, as well as other wild plant and animal foods. These wild plants continued to be utilized after the beginning of agriculture (Terasawa and Terasawa 1981), but only a few became domesticated, such as the vegetable species Cryptotaenia canadensis (L.) DC. subsp. japonica (Hassk.) Hand.-Mazz., Petasites japonicus (Siebold et Zucc.) Maxim., and Dioscorea japonica Thunb. Although not important vegetables now, they might have been eaten before the modern age.

Among the native species listed (Table 2), Castanea crenata is the only one to become a major cultivated crop. It is also one of the few species domesticated in pre-modern times, along with Myrica rubra and Pyrus ussuriensis var. ussuriensis. Cultivation of C. crenata may have begun in prehistoric times, and its utilization for timber was also important in ancient times (Amino 2001). Myrica rubra grows wild in evergreen forests in middle and western Japan and has long been used as firewood. Its cultivation as a fruit tree may have begun in the late Edo period (19th century). However, the present leading cultivars are said to have been introduced from China (Wada 2000).

This paucity of cultivated native species was perhaps influenced by the presence of many introduced fruit trees. Large fleshy fruits are lacking among Japanese native species. Mammal-dispersed fruits, which are usually larger than bird-dispersed fruits, are rare among Japanese temperate species, occurring only in Akebia, Stauntonia, Actinidia, Pyrus, Chaenomeles, and Cornus kousa. The first three have been locally commercialized in modern times, as described below. Subtropical genera with mammal-dispersed fruits, such as Syzygium and Toddalia, have not been cultivated.

Recent domestication

High economic growth and cultural westernization after World War II increased the diversity of diet and foodstuffs in Japan. The consumption of fruits increased in both quantity and quality (such as jams, juices, and confectioneries). However, consumption stagnated and fell after the high economic growth ended, and some production areas tried to convert existing crops into new products (Uchiyama 1996). In areas depopulated by the high economic growth, various projects for reactivation of the local economy have been attempted since the 1960s. In the agricultural sector, fruit crops were developed as specialty products and matched with tourism strategies. Fruits and nuts are produced not only as regular products, but also as value-added products for gifts and souvenirs.

Although major fruits such as citrus, apple, and table grape are grown for product differentiation strategy, some minor fruits such as introduced berry and tropical fruit species also have a role. The most specialized products are newly domesticated native fruit trees. Among 8 genera with 11 species (Table 3), Vitis coignetiae and Actinidia spp. (A. arguta, A. polygama and A. rufa) have congeneric major fruit species, V. vinifera and A. deliciosa, respectively. Vaccinium also has many cultivated species, including blueberry and cranberry, in temperate and subarctic climate zones in other countries. Lonicera caerulea is also cultivated in Russia and North America. Recently, Japanese cultivars were introduced into the USA and their adaptability to the climate was evaluated (Hummer et al. 2012, Thompson and Chaovanalikit 2002). The other five genera do not have any other major species grown for food in other countries. The most notable are Akebia (A. quinata and A. trifoliata) and Stauntonia (S. hexaphylla), both endemic to East Asia (Takhtajan 1986), and thus almost unknown in the West as fruit.

Table 3 New commercial cultivation of Japanese native fruit trees

Species	Production (t)		Representative Regions	Source
	2003	2012
Akebia quinata and A. trifoliata	25.7	8.9	Yamagata, Ehime, Akita
Stauntonia hexaphylla			Shiga	1)
Vitis coignetiae	135.6	186.7	Iwate, Yamagata, Hokkaidō
Rosa rugosa			Hokkaidō, Aomori	2), 3)
Elaeagnus multiflora			Aomori	4)
Vaccinium oldhamii			Fukushima, Nagano, Nara	5), 6), 7)
Actinidia arguta	13.1	10.6	Fukushima, Kagawa, Yamagata
A. polygama	1.9	—	Akita
A. rufa			Miyazaki	8)
Lonicera caerulea	60.0	90.2	Hokkaidō, Aomori

Production data were drawn from the website of the Ministry of Agriculture, Forestry, and Fisheries (http://www.e-stat.go.jp/SG1/estat/List.do?lid=000001129267)

Information on other plants was based on the following websites: 1) http://www.nube.jp/mube.html, 2) http://www.n-slow.com/item_detail/itemCode,su-1591/, 3) http://www.umai-aomori.jp/know/sanchi-report/146.phtml, 4) http://www.morikaju.jp/kudamono-natu.html, 5) http://www.nico2farm.jp/?page_id=21, 6) http://www.iijan.or.jp/oishii/products/fruit/post-1424.php, 7) http://natsuhaze.com/index.html, 8) http://www.yappamiyazaki.jp/store/search.php?codeNumber=1265765213

As these native species have a niche market, both their area and quantity of production are limited, and production has fluctuated. Except for Vitis coignetiae and Lonicera caerulea, the commercial cultivation of these native plants is extremely limited, possibly with as few as half a dozen growers at the fewest.

Although species of Pinus, Amelanchier, Cornus, Crataegus, and Sorbus are cultivated in other parts of the world, Japanese species are not utilized. They may have been eaten by indigenous people, but archaeological or ethnological evidence is lacking. The rarity of Crataegus and Sorbus (except for S. commixta) in Honshū and further south may be a reason. Seed of Pinus has been imported from Korea since the Middle Ages (von Verschuer 2006). However, there is no evidence for the utilization of Japanese species. Only imported seeds might have been consumed, and historical references (e.g., Minamoto 930s) might have been nothing more than citations from the Chinese literature. Although Pinus is common in the Japanese flora, P. koraiensis, which is the main edible species, is rare and may have been neither cultivated nor collected in the wild.

Future conservation

Horticultural and breeding studies have included Japanese wild species of Vitis, Malus, Pyrus, and Actinidia, which are congeneric with major fruit tree species, along with other wild species (e.g., Janick and Moore 1996, Moore and Ballington 1990). However, the conservation of these wild species, both in situ and ex situ, is inadequate: 84 taxa in Table 2 are nominated in the Japanese National Red List (Ministry of Environment of Japan 2012), including two species of Vitis (V. amurensis and V. romanetii), two of Malus (M. hupehensis and M. spontanea), and two of Pyrus (P. calleryana and P. ussuriensis). The Red List only contains threatened plants and has no legal standing for the prohibition of picking and selling. Ex situ conservation is also precarious. Until recently, the NIAS Genebank, which is the Japanese national genebank for agricultural crops, has held few or no germplasm accessions of these native species. Other facilities such as botanical gardens are in a similar situation. To address this lack, extensive explorations have been performed for Pyrus (Iketani et al. 2005, 2006, 2008, Iketani and Mase 2009), Malus (Iketani et al. 2006, 2007, 2008, Iketani and Mase 2009, 2013, 2016), and Vitis (Iketani et al. 2014) in the past 10 years.

Recent advances in molecular population genetics have revealed that a species can be genetically differentiated when a genetic barrier among subpopulations exists. Therefore, a widely distributed species is likely to be differentiated where geographical barriers to gene flow, such as seas or high mountains, intervene, unless long-distance dispersal is possible. For example, Pyrus ussuriensis (sensu lato) is widely distributed in northeastern China, eastern Russia (Amur to Primorsky), the Korean Peninsula, and central and northern Honshū. Iketani et al. (2010a, 2012) revealed that native populations on the Asian continent, in central Honshū, and in northern Honshū are highly differentiated. Thus, it will be necessary to evaluate genetic differentiation within taxa to maximize the collection of genetic diversity.

Conservation of minor plants is more problematic, especially for the purpose of agricultural genetic resources. Their economic importance is limited. Basic information such as past ethnological utilization is necessary, as well as research for agricultural and industrial utilization. For example, Matsushima et al. (2013) newly reported several edible uses of plants on the basis of interviews in a mountain village in central Honshū. For the conservation of these species, several explorations have been performed (Iketani et al. 2010b, Ito 2011, 2012, Ito and Sugawara 2006, 2007, 2008, 2009, 2010). The collected germplasm is conserved in NIAS Genebank (http://www.gene.affrc.go.jp/index_en.php), along with the abovementioned Pyrus, Malus, and Vitis germplasm.

Preservation of collected germplasm also has difficulty because most of fruit trees have to be stored in the form of living plants. As it costs enormously, only national or international organizations have been capable to preserve fruit tree genetic resources. However, smaller organizations such as local governments and communities, private companies, non-governmental organizations and farmers could have a role (Frese et al. 2014, Maxted et al. 2011). We have to seek a new way that enables their participation. In Japan, on farm conservation of local vegetables can be cited as examples (Nishikawa 2012). Similar approaches in minor fruits and local fruit landraces could be possible by combining various potential benefits of germplasm collections such as local culture, education and tourism, not only economic ones.

Acknowledgement

I thank the anonymous reviewers for their helpful comments.

Literature Cited

• Ainu Museum (2015) Ainu to Shizen Digital Museum (Digital Museum of the Ainu and Nature). (http://www.ainu-museum.or.jp/siror/).
•  Amano,  T. (1982) Ryūkyū Rettō Yūyō Jumokushi (Useful Woody Plants of the Ryūkyū Peninsula). Ryūkyū Rettō Yūyō Jumokushi Kankōkai, Naha, 255 pp.
•  Amino,  Y. (2001) Chūsei Minshū no Seigyō to Gijutsu (The Development of Crafts and Industries in Japan’s Medieval Society). University of Tokyo Press, Tokyo, 285 pp.
•  Frese,  L.,  A.  Palmé and  C.  Kik (2014) On the sustainable use and conservation of plant genetic resources in Europe. Report from Work Package 5 “Engaging the user Community” of the PGR Secure project “Novel characterization of crop wild relative and landrace resources as a basis for improved crop breeding” (http://www.nordgen.org/index.php/en/Plants/Innehaall/Workshops-Conferences/Plant-Genetic-Resource-Workshop-2013/Final-report-and-policy-paper).
• Fujiwara, T., T. Fujiwara et al. (Names of other authors are unknown) (eds.) (927) Engishiki (Procedures of the Engi Era). English translation by F.G. Bock is available at the Japanese Historical Text Initiative of the University of California at Berkeley (http://pnc-ecai.oiu.ac.jp/jhti/Engi Shiki editions and copyrights.html).
•  Fukuoka,  I. (1995) Ainu Shokubutsushi (Folkloric Flora of the Ainu People). Sōfūkan, Tokyo, 241 pp.
•  Hatakeyama,  T. (1989) Jōmonjin no Matsuei Tachi, Hie to Ki no Mi no Seikatsushi (Descendants of Jōmon People, Food Style with Japanese Millet and Nuts). Sairyūsha, Tokyo, 333 pp.
• Hokkaido Institute of Public Health (2015) Ainu Minzoku no Yūyō Shokubutsu (Useful Plants for the Ainu people). (http://www.iph.pref.hokkaido.jp/yakuyosyokubutuen/ainuyuyosyokubutu_uni21.htm).
•  Hori,  S. and  T.  Hori (1997) A cultural history of Ginkgo biloba in Japan and the generic name ginkgo. In:  Hori,  T.,  R.W.  Ridge,  W.  Tulecke,  P. Del.  Tredici,  K.  Trémouillaux-Guiller and  H.  Tobe (eds.) Ginkgo biloba—A Global Treasure from Biology to Medicine. Springer, Tokyo, pp. 385–411.
•  Hudson,  M.J. (2007) Japanese Beginnings. In: Tsutsui, W.M. (ed.) A Companion to Japanese History, Blackwell, Oxford, pp. 13–29.
•  Hummer,  K.E.,  K.W.  Pomper,  J.  Postman,  C.J.  Graham,  E.  Stover,  E.W.  Mercure,  M.  Aradhya,  C.H.  Crisosto,  L.  Ferguson,  M.M.  Thompson et al. (2012) Emerging Fruit Crops. In:  Badenes,  M.L. and  D.H.  Byrne (eds.) Fruit Breeding, Handbook of Plant Breeding 8, Springer, Berlin, pp. 97–147.
•  Iketani,  H.,  N.  Mase and  Y.  Sato (2005) Exploration and collection of Pyrus ussuriensis var. hondoensis in Yamanashi and Nagano Prefectures. Annu. Rep. Explor. Introd. Plant Genet. Res. 21: 37–43.
•  Iketani,  H.,  N.  Mase and  Y.  Sato (2006) Exploration and collection of Pyrus and Malus genetic resources in Northern Tohoku region. Annu. Rep. Explor. Introd. Plant Genet. Res. 22: 13–21.
•  Iketani,  H.,  N.  Mase and  Y.  Sato (2007) Exploration and collection of Malus genetic resources in Nagano and Yamanashi Prefectures. Annu. Rep. Explor. Introd. Plant Genet. Res. 23: 55–61.
•  Iketani,  H.,  N.  Mase and  Y.  Sato (2008) Exploration and collection of rosaceous fruit tree genetic resources in Toyama and Ishikawa Prefectures. Annu. Rep. Explor. Introd. Plant Genet. Res. 24: 55–61.
•  Iketani,  H. and  N.  Mase (2009) Exploration and collection of Malus and Pyrus genetic resources in Tochigi Prefecture. Annu. Rep. Explor. Introd. Plant Genet. Res. 25: 61–69.
•  Iketani,  H.,  T.  Yamamoto,  H.  Katayama,  C.  Uematsu,  N.  Mase and  Y.  Sato (2010a) Introgression between native and prehistorically naturalized (archaeophytic) wild pear (Pyrus spp.) populations in northern Tohoku, northeast Japan. Conserv. Genet. 11: 115–126.
•  Iketani,  H.,  K.E.  Hummer,  J.D.  Postman,  H.  Imanishi and  N.  Mase (2010b) Collaborative exploration between NIAS Genebank and USDA ARS (U.S. Department of Agriculture, Agricultural Research Service) for the collection of genetic resources of fruit and nut species in Hokkaidō and the northern Tōhoku Region. Annu. Rep. Explor. Introd. Plant Genet. Res. 26: 13–26.
•  Iketani,  H.,  H.  Katayama,  C.  Uematsu,  N.  Mase,  Y.  Sato and  T.  Yamamoto (2012) Genetic structure of East Asian cultivated pears (Pyrus spp.) and their reclassification in accordance with the nomenclature of cultivated plants. Plant Syst. Evol. 298: 1689–1700.
•  Iketani,  H. and  N.  Mase (2013) Exploration and collection of two crabapple species, Malus spontanea Makino and “Takanabe kaidō,” in Southern Kyūshū, Japan. Annu. Rep. Explor. Introd. Plant Genet. Res. 29: 119–125.
•  Iketani,  H.,  A.  Kono,  Y.  Ban,  S.  Yamamoto and  N.  Mase (2014) Collection of a rare and endangered wild grapevine species, Vitis kiusiana Momiyama, in Southern Kyūshū, Japan. Annu. Rep. Explor. Introd. Plant Genet. Res. 30: 101–107.
•  Iketani,  H. and  N.  Mase (2016) Collection of wild and cultivated rare Malus genetic resources in Northern Kyūshū, Japan. Annu. Rep. Explor. Introd. Plant Genet. Res. 31 (in press).
•  Ito,  Y. and  Y.  Sugawara (2006) Exploration and collection of akushibamodoki (Vaccinium yakushimense Makino) in Yakushima. Annu. Rep. Explor. Introd. Plant. Genet. Res. 22: 33–35.
•  Ito,  Y. and  Y.  Sugawara (2007) Exploration and collection of nagabonatsuhaze (Vaccinium sieboldii Miq.) in Aichi Prefecture and aragenatsuhaze (Vaccinium ciliatum Thunb.) in Hiroshima Prefecture. Annu. Rep. Explor. Introd. Plant Genet. Res. 23: 63–67.
•  Ito,  Y. and  Y.  Sugawara (2008) Exploration and collection of tsurukokemomo (Vaccinium oxycoccus L.) and kuromamenoki (Vaccinium uliginosum L.) in Nemuro City in Hokkaido. Annu. Rep. Explor. Introd. Plant Genet. Res. 24: 79–83.
•  Ito,  Y. and  Y.  Sugawara (2009) Exploration and collection of muninshashanbo (Vaccinium boninense Nakai) in Chichijima Island, the Ogasawara Islands in Tokyo Metropolitan Prefecture. Annu. Rep. Explor. Introd. Plant Genet. Res. 25: 53–59.
•  Ito,  Y. and  Y.  Sugawara (2010) Exploration and collection of keyonomi (Lonicera caerulea L. subsp. edulis (Regal) Hultén) and kurominouguisukagura (Lonicera caerulea L. subsp. edulis (Regal) Hultén var. emphyllocalyx (Maxim.) Nakai) in the Yufutsu Wilderness in Hokkaido. Annu. Rep. Explor. Introd. Plant Genet. Res. 26: 7–12.
•  Ito,  Y. (2011) Exploration and collection of kurominouguisukagura (Lonicera caerulea L. subsp. edulis (Regel) Hultén var. emphyllocalyx (Maxim.) Nakai) in three wetlands in eastern Hokkaido. Annu. Rep. Explor. Introd. Plant Genet. Res. 27: 35–39.
•  Ito,  Y. (2012) Exploration and collection of shashanbo (Vaccinium bracteatum Thunb.) on Yakushima island, Kagoshima prefecture. Annu. Rep. Explor. Introd. Plant Genet. Res. 28: 105–111.
• Iwatsuki, K., T. Yamazaki, D.E. Boufford and H. Ohba (eds.). (1993–2016). Flora of Japan Vol. 1–4, Kodansha Scientific, Tokyo.
• Janick, J. and J.N. Moore (eds.) (1996) Fruit Breeding Vol. I–III, Wiley, New York.
•  Kajita,  T. (2003) Cycadophyta, Ginkgophyta, Coniferophyta and Magnoliophyta. In: Union of Japanese Societies for Systematic Biology (ed.) Japanese Biota Species Number Survey, 1st Edition. (http://ujssb.org/biospnum/search.php).
•  Katayama,  H. and  C.  Uematsu (2006) Pear (Pyrus species) genetic resources in Iwate, Japan. Genet. Resour. Crop Evol. 53: 483–498.
•  Katayama,  H.,  H.  Amo,  T.  Wuyun,  C.  Uematsu and  H.  Iketani (2016) Genetic structure and diversity of the wild Ussurian pear in East Asia. Breed. Sci. 66: 90–99.
•  Keally,  C.T. (2009) Japanese Archaeology. (http://www.t-net.ne.jp/~keally/index.htm).
•  Kikuchi,  A. (1948) Kaju Engeigaku Jōkan (Horticulture of Fruit Trees, Vol. 1,). Yokendo, Tokyo, 528 pp.
•  Kitamura,  S. (1979) Rosaceae. In:  Kitamura,  S. and  G.  Murata (eds.) Coloured Illustration of Woody Plants of Japan 2, Hoikusha, Osaka, pp. 1–97.
•  Kobayashi,  A. (1990) Bunka to Kudamono (Culture and Fruits). Yokendo, Tokyo, 198 pp.
•  Koike,  H. and  K.  Miyagawa (1974) Studies on the blueberries, 1: On characteristics and propagations of the wild blueberry (Vaccinium uliginosum) in Japan. Nagano Hort. Exp. Sta. 11: 1–10.
• Library of Congress and American Library Association (2012) The ALA-LA Romanization Tables. (http://www.loc.gov/catdir/cpso/roman.html).
•  Liu,  M.-J. (1998) Zhong guo ye sheng guo shu (Wild fruit trees of China), Agricultural Press of China, Beijing, 418 pp.
•  Matsushima,  K.,  K.  Nemoto,  A.  Tsurukawa,  Y.  Kato,  S.  Ohsaki,  Y.  Nishida and  M.  Minami (2013) Investigation on wild edible plants in Ohshika, Simo Ina, Nagano, Japan. J. Fac. Agric. Shinshu Univ. 49: 43–50.
•  Matsuyama,  T. (1982) Ki no Mi (Ethnology of Tree Nuts). Hosei University Press, Tokyo, 371 pp.
• Maxted, N., M.E. Dulloo, B.V. Ford-Lloyd, L. Frese, J. Iriondo and M.A.A.P. de Carvalho (eds.) (2011) Agrobiodiversity Conservation Securing the Diversity of Crop Wild Relatives and Landraces. CABI, Wallingford, 392 pp.
• Minamoto, S. (930s) Wamyō Ruijushō (Japanese Names, Classified and Annotated). (Digital images of a later publication (Nawa, D. (ed.) 1617) are available at http://dl.ndl.go.jp/info:ndljp/pid/2606770).
• Ministry of the Environment of Japan (2012) The Fourth Red List, Plant I, II. (http://www.biodic.go.jp/rdb/rdb_f.html).
• Mittermeier, R.A., P.R. Gil, M. Hoffman, J. Pilgrim, T. Brooks, C.G. Mittermeier, J. Lamoreux and G.A.B. da Fonseca (eds.) (2004) Hotspots Revisited: Earth’s Biologically Richest and Most Threatened Terrestrial Ecoregions, University of Chicago, Chicago, 390 pp.
• Moore, J.N. and J.R. Ballington, Jr. (eds.) (1990) Genetic Resources of Temperate Fruit and Crops Vol. 1–2. International Society for Horticultural Science, Wageningen, 975 pp.
• Nishikawa, Y. (ed.) (2012) Seibutsu Tayōsei wo hagukumu Shoku to Nō (Food and Agriculture nurturing the Biodiversity). Commons, 240 pp.
•  Ohwi,  J. (1965) Flora of Japan, Smithsonian Institution, Washington DC. 1067 pp.
•  Omatsu,  S. and  S.  Tsuji (2001) Early Jomon plant macroremains from the Ireibaru C Site in south Okinawa, southwestern Japan. Jpn. J. Histor. Bot. 10: 17–32.
•  Sarashina,  G. and  K.  Sarashina (1976) Kotan Seibutsuki I, Jumoku Zassō hen (Biota of Ainu Settlements I, Woody and Herbaceous Plants). Hosei University Press, Tokyo, 265 pp.
• Satake, Y., H. Hara, S. Watari and T. Tominari (eds.) (1989) Wild Flowers of Japan, Woody Plants Vol. 1–2, Heibonsha, Tokyo.
•  Sato,  H. and  T.  Nohara (1997) Nansei shotō ni okeru kyūkōshoku to shiteno yasei dōshokubutsu shigen no riyō (Use of wild plant and animal resources during famine in Nansei Islands). Okinawa Minzoku Kenkyū 17: 41–59.
•  Takhtajan,  A. (1986) Floristic Regions of the World (Transl. by T.J. Crovello). Univ. Calif. Press, Berkeley, 522 pp.
•  Taneishi,  Y. (2014) Kodai Shokuryō Kakutoku no Kōkogaku (The Archaeology of Food Acquisition in the Ancient Japan). Dōseisha, Tokyo, 325 pp.
•  Tawada,  S. (1982) Shushoku no Hensen (History of Staple Diets) Shin-okinawabungaku 54: 40–48.
•  Terasawa,  K. and  T.  Terasawa (1981) Yayoi Jidai Shokubutsushitsu Shokuryō no Kisoteki Kenkyū (Basic Research on Plant-Based Diets in the Yayoi Period). Studies in Archaeology: Proc. Kashiwara Archaeol. Inst. 5: 1–129.
•  Thompson,  M.M. and  A.  Chaovanalikit (2002) Preliminary observations on adaptation and nutraceutical values of blue honeysuckle (Lonicera caerulea) in Oregon, USA. Acta Hortic. 626: 65–72.
•  Uchiyama,  Y. (1996) Kaju Seisan Chiiki no Kōsei (Structure of Fruit Production Area). Taimeido, Tokyo, 229 pp.
•  von Verschuer,  C. (2006) Across the Perilous Sea. Japanese Trade with China and Korea from the Seventh to the Sixteenth Centuries. Cornell Univ., N.Y., 226 pp.
•  Wada,  H. (2000) Yamamomo (Bayberry) In: Rural Culture Association Japan (ed.) Kaju Engei Dai Hyakka 15, Jōryoku Tokusan Kaju (Encyclopedia of Fruit Trees 15, Evergreen Local Fruits), Rural Culture Association Japan, Tokyo. pp. 335–345.
•  Watanabe,  M. (1975) Jōmon Jidai no Shokubutsushoku (Plant-Based Diets of the Jōmon Period). Yuzankaku, Tokyo, 187 pp.
•  Yonekura,  K. (2012) An Enumeration of the Vascular Plants of Japan. Hokuryukan, Tokyo, 379 pp.
•  Yonekura,  K. and  T.  Kajita (2003–) YList, Index of Common Names and Scientific Names of Japanese Plants. (http://ylist.info/index.html).