Ethnobotanical review of traditional use of wild food plants in Japan

Abstract

Background

Japan, which has a diverse climate, is home to 8118 species of wild vascular plants, with more than 1000 of these species considered edible. However, there are fewer studies on the use of wild food plants in Japan than in other parts of the world. This research aims to provide an ethnobotanical review of the traditional food use of wild plants in Japan. It draws upon the largest database of traditional Japanese foodways, with a specific focus on the period approximately 1930. This occurred prior to Japan’s rapid economic growth, which resulted in significant changes in the use of wild plants.

Methods

The use of wild food plants in Japan was reviewed by studying the collection of Japanese foodways (Nihon no shokuseikatsu zenshu), which is the largest database on Japanese traditional foodways and contains records of approximately 52,000 dishes, including food uses of wild plants. The review extracted the local and common names, use locations, uses, processing and cooking methods, habitats and other relevant details pertaining to the reported use of wild food plants. This information was subsequently analyzed via Excel.

Results

A total of 268 taxa belonging to 87 families used in Japan approximately 1930 were documented. Asteraceae was the most frequently reported family as well as the most species-rich family. In terms of use, vegetables composed the largest group, followed by dessert fruits. The majority of species have been documented in only a limited number of reports. The review revealed local traditional uses of plants, including the use of plants as binders for making rice cake, the selection of plants according to their sex, and techniques for detoxifying toxic plants.

Conclusion

A comparison with those of previous studies on wild species used in other Asian regions revealed a similar preference for vegetables. However, notably, in Japan, ferns are also consumed in considerable quantities. Conversely, further elucidation is clearly needed with respect to certain matters, including the perception of plant sex and the relationships between diverse ash components and detoxification techniques. It is evident that further ethnobotanical research is needed, both in the form of an examination of ethnographic records and in the field, to gain a deeper understanding of the use of wild food plants in Japan.

Introduction

Among more than 50,000 edible plant species in the world, only nine account for more than 66% of all crop production [1], while there are diverse land- and culture-based food uses of wild plants in different parts of the world. Understanding the patterns of use and cultural significance and value of wild food plants worldwide has been an important challenge in terms of ecology, culture, nutrition, economics and agriculture, as well as of genetic resources and biocultural diversity [2,3,4,5]. Previous ethnobiological studies have investigated the use of wild food plants in different populations around the world. In Europe in particular, there is an accumulation of ethnobotanical studies and reviews in various regions and countries [6,7,8,9,10,11,12,13,14]. An international review noted that most studies on gatherings are from the Americas, Europe, Central Asia and Africa, and there are fewer literatures and studies available from Asia [3]. The studies on wild edible plants and traditional knowledge in Asia are mainly in China, Southeast Asia and Central Asia, covering various social populations, such as farmers, indigenous communities and ethnic minorities [15,16,17,18,19,20,21,22,23,24,25,26]. In South Korea in East Asia which flora and climate are similar to Japan, studies have been conducted on the gathering practices and knowledge of wild edible plants in specific geographical areas including islands [27,28,29], and on the presence of these plants in the marketplace [30].

Japan, the subject of this research, is located off the northeast seaboard of the Eurasian continent and has a surface area of nearly 378,000 km². The climate in Japan is diverse, with variations from subarctic in the northern regions to subtropical in the southern areas. A total of 8118 species of wild vascular plants are known to be grown in Japan [31], with more than 1000 of these species considered edible [32].

The use of wild food plants and mushrooms has been the subject of considerable interest in various academic disciplines in Japan. This has focused on a range of topics, including natural resources, nontimber forest products (NTFPs) and forest management in forestry [33,34,35]; the distribution of natural resources and territory in human geography [36, 37]; and the practice of gathering and understanding human–nature relations in folklore studies and anthropology [38,39,40,41].

Among these traditional interdisciplinary interests in wild food plants, for example, in the field of forestry, some studies have investigated the potential for the versatile use of wild plant resources, in the context of the difficult economic situation of private forest management and agroforestry in the late 1970s and 1980s. This was driven by the recognition that a combined agroforestry management approach, rather than one focused solely on timber production, could offer a more sustainable and resilient solution. The studies encompass an understanding of the state of multipurpose use of wild plants in Japan at the time, including food, folk art and craft, medicine and ritual use. Additionally, they address cultivation techniques for wild plants and urban consumers’ preferences for mushrooms and wild vegetables.

The use of wild food plants in Japan, as in other global contexts, was primarily driven by the need to source food to meet subsistence requirements and to provide a source of nutrition during periods of famine. In particular, during the Edo period (1603–1868), there was a history of nationwide famines due to a combination of various causes, including abnormal weather conditions such as cold damage and drought. In the context of these famines, several books on wild edible plants were published to guidance on how to choose, prepare and eat these plants. To illustrate, the Yonezawa clan, currently situated in Yamagata Prefecture, published Hanroshu (collection of famine foods) in 1783 and Katemono (emergency foods) in 1802, by the order of Youzan Uesugi (1751–1822), a daimyo, lord of the Yonezawa clan and they introduced a total of 144 plant species. Another famous book is Bikousomokuzu (famine preparation botanical drawings) published in 1833,¹ primarily authored by the physician Seian Takebe (1712–1782), which introduced 104 species with accompanying illustrations and disseminated throughout Japan.

Japanese folklore and anthropological studies have noted the cultural role of wild food plants, such as how they serve as intermediaries for communication and social interaction, particularly in the form of gift-giving practices. These studies have suggested that the foraging practices are not merely the acquisition of food in Japan; rather, it is a process through which perceptions and sense of nature, resources, and community are shaped [41]. These studies referred to the cultural significance of wild food plants including those used as special foods and offerings for rituals, ceremonies and special occasions, including the New Year and Bon festival [35]. Manyoshu, Japan's oldest anthology of waka poetry, assembled in after 759 CE, also contains poems describing scenes of people gathering wild food plants in the mountains and fields. These poems, in particular, offer insight into the practice of foraging plants during the spring season. Thus, previous studies demonstrate that wild food plants not only satisfy the nutritional requirements of the Japanese population, but also possess cultural uses and meanings that are deeply rooted in the diverse regions of Japan.

Folklore studies also indicate that foraging in Japan constituted one component of a multifaceted system of livelihoods [41]. Although rice cultivation, which produces the staple food rice, tends to be regarded as the primary source of livelihood in Japan, numerous mountain villages have sustained themselves by integrating a range of practices, including slash-and-burn farming, forestry, hunting, fishing, charcoal production, and also foraging. Foraging practices in Japan have been shown to vary depending on the region, village, household, and time period. These practices have ranged from gathering for subsistence to pursuing cash value.

On the other hand, the number of studies that have been conducted to determine the actual state of wild food plants uses at the national level is very limited; except a questionnaire survey conducted approximately 1980 which revealed that more than 250 species of wild vegetables were used in Japan excluding Okinawa [42]. Several previous studies in Japan have employed a variety of methods, including questionnaires, field surveys, and literature reviews, to ascertain the actual pattern of the use of wild food plans with focus on specific prefecture and area. For example, a study suggested that 178 species from 46 families of vascular plants and 10 species of ferns are consumed as wild plants in northern Japan [40]. The same study also revealed that 101 species of seeds, including nuts and fruits belonging to 34 families, are consumed for medicinal and food purposes. Another study conducted in Nagano Prefecture based on literature reviews revealed the use of 161 species of wild vegetables and 100 species of wild fruits in traditional foods between 1868 and 1955 [43]. A more recent study conducted in the Noto Peninsula, Ishikawa Prefecture, revealed the presence of 176 species belonging to 65 families of edible plants, however, the number of species actually consumed was limited [44]. In Fukushima Prefecture in the Tohoku Region, a total of 45 taxa of wild vegetables and 26 taxa of nuts were used; however, these species have been used less frequently in recent years [45]. It should be noted that most of these previous studies were published in Japanese and therefore limited accessibility to international audience.

It is suggested that the use of wild food plants is declining in Japan as a whole [35]. In particular, the postwar period of rapid economic growth from the late 1950s onward saw a shift in the use of wild food plants [35, 39, 45, 46]. During this period, the social and natural environment, including industrial patterns, lifestyles and land use, underwent substantial transformation [47]. The study in Fukushima mentioned earlier considered several specific factors that have contributed to the decline in the use of wild food plants [45]. These include social changes, such as changing lifestyles and the introduction of purchasable foods, and environmental changes, including land development, the use of pesticides, and the reduction in habitats.

Conversely, since the period of economic growth, the popularity of foraging and consuming wild food plants has increased [38]. This popularity is referred to as the sansai (mountain vegetable) boom and can be considered the period when the new term ‘sansai’ to describe mountain vegetables spread, especially among urban populations. This phenomenon has given rise to novel trends in recreational foraging [35] and the publication of introductory books and illustrated reference books on wild food plants. These developments have also facilitated the utilization of previously unused species in some region [45]. In more recent years, the practice of recreational foraging wild food plants has retained a notable degree of popularity. In particular, within the Tohoku and Hokuriku regions, the foraging and eating of wild food plants have been utilized as a means of promoting local tourism. At the same time, there have been concerns regarding the depletion and deterioration of resources due to unplanned collection by external parties, as well as incidents resulting from the inadvertent collection of poisonous species including mushrooms.

Given these backgrounds, this research aims to provide an ethnobotanical review of the traditional food use of wild plants in Japan via the largest database of traditional Japanese foodways, with a specific focus on approximately 1930, which was before rapid economic growth, when major changes in the use of wild plants occurred. The specific focuses of this study were: (1) to identify how many species of plants were used as food in Japan around 1930, (2) to analyze which plant families and species were commonly used in local food categories, and (3) to understand the cultural uses of wild species in the context of Japanese traditional food culture.

Methods

Materials

The use of wild food plants in Japan was reviewed by studying the collection of Japanese foodways (Nihon no shokuseikatsu zenshu) [48]. The collection aimed to archive Japanese traditional foodways on the basis of an oral history of dietary habits during the late 1920s and early 1930s. The data were collected from interviews with 5,000 speakers who were mostly women in their late 70s or older at the time of the survey and were involved in food preparation around the late 1920s to early 1930s. The collection was selected as it is the largest database on Japanese traditional foodways and contains records of approximately 52,000 dishes, including daily recipes as well as culinary uses of wild plants as well as on the basis of its uniformity of criteria and format, which were applied consistently throughout all prefectures in Japan during the survey. The collections consisted of 50 volumes covering all 47 prefectures from Hokkaido to Okinawa as well as one indigenous population, Ainu, in Hokkaido. This review examined 47 volumes, one for each prefecture (Fig. 1). The review extracted the local and common names, use locations, uses, processing and cooking methods, habitats and other relevant details pertaining to the reported use of wild food plants when available. This information was subsequently analyzed via Excel.

Fig. 1

Locations of regions and prefectures in Japan

Wild species

In this study, wild plants refer to noncultivated vascular plants, as suggested by a previous study [7]. Only species that could be identified as noncultivated plants were extracted on the basis of their description, including their habitats, such as mountains, fields, and river margins, as well as their growth conditions. In certain instances, both wild and cultivated forms, such as Eutrema japonicum, Diospyros kaki, Castanea crenata, and Phyllostachys edulis, can be found growing in the same study area. Only those species that are explicitly described as wild forms were included. Species that grow in areas with some degree of human intervention, such as the banks of rice paddies, or those that were cultivated but have escaped, such as Eleutherococcus sieboldianus, are also included if they are described as wild plants in the literature.

In the collections, the local and Japanese common names of the plants are provided, with the exception of those for which only one name is available. In cases where only the local name was known, the common name was identified by consulting the Collection of Plants Dialects of Japan [49] and the Folklore Research Card Collection Database, which was collected by Tama Saito, an independent folklore researcher who collected folklores that included uses of plants throughout Japan [50], and other literature specific to each study area [51,52,53,54,55,56]. A checklist of Japanese plant names [57] was used to check the distribution of the species as well as to determine the scientific name from the Japanese name. The scientific name follows Plants of the World Online [58], and synonyms have been corrected.

Categories

First, the study included plants that are consumed as food or beverages, while plants used only as famine food or medicines were excluded. In accordance with the Economic Botany Data Collection Standard [59], the uses of plants were first categorized into the following food categories: cereals, pseudocereals, pulses, nuts, dessert fruits, vegetables (including green and root/tuber vegetables), leaf protein concentrates, starches, oils/fats, gums/mucilages, sugars, and other food types. The vegetable category also included plants that are used in relatively small quantities and serve as flavor-adding seasonings. Among these categories, the categories of cereals, pseudocereals, pulses, leaf protein concentrates, gums/mucilages, and sugars were excluded, as there were no reports in these categories.

In addition, by referring to folk perceptions of food uses, snacks, beverages, and binders were added as categories. Plants eaten between or after meals, with the exception of dessert fruits, were classified as snacks. Beverages include both alcoholic beverages such as liquors and nonalcoholic beverages such as tea. Binders include plants that are used to combine food ingredients. This usage is called "tsunagi" in Japanese and is used to make various foods such as mochi (rice cakes), dango (rice dumplings), and soba (buckwheat noodles). In total, 9 types of food categories were established as follows: nuts, dessert fruits, vegetables, starches, oils/fats, snacks, beverages, binders, and other food types.

The plant parts used were classified into the following categories: entire plants, unspecified aerial parts, galls, stems, bark, leaves, inflorescences, infructescences, seeds, roots, exudates, shoots, and propagules. When parts used were not specified in the literature, they were classified as N/A (not available).

Data analysis

In this study, a report refers to a citation of the use of a wild food plant species (or taxa) in the literature at a single study site. For example, at one study site, if the fruit of species A was eaten as a dessert fruit and the shoot was eaten as a vegetable, the number of reports was counted as one. On the other hand, when the analysis was conducted in relation to the food categories and parts used, the calculation was based on the number of species in each category. In other words, if species A was eaten as a vegetable or fruit, it was counted as one species in each food category.

Some reports were able to be identified only at the genus or subfamily level. The reason for this was that a single folk name encompassed multiple species. For example, azami is a general term for Cirsium spp. (Asteraceae), similar to the English thistle, and there are more than 150 species of azami in Japan. Similarly, noichigo or kiichigo is a generic name for strawberry plants that grow wild. Most of them belong to Rubus spp. (Rosaceae), and there are more than 30 wild species of Rubus spp. in Japan. The diversity of folk taxa and their species are noteworthy [6]. However, to avoid confusion in calculations, these folk taxa identified to the genus or subfamily level were calculated as one taxon, only if no botanical species from the genus or subfamily were recorded at the study site.

Results and discussion

General data

Among the 310 study sites across Japan, 278 reported the food use of wild plants. The study sites where no use was reported were mostly urban and coastal areas. In total, 3699 reports were recorded, 36 of which could not be identified by scientific names. As a result, 251 species belonging to 86 families that were used as food and beverages approximately 1930 in Japan were recorded. In addition, some reports (456 reports) were able to be identified only at the genus or subfamily level. Among the 17 such folk taxa, 16 genera and 1 subfamily belonging to 13 families were identified. A total of 268 taxa belonging to 87 families were used in Japan, including those specified above.

All of the taxa documented in this study have been previously reported as edible for instance, in two encyclopedias which cover most of the wild edible plants in Asia [60, 61] except Maianthemum viridiflorum. This study identified one report of a young stem of M. viridiflorum being boiled and consumed as a vegetable in the vicinity of a mountain lodge in Tateyama, Toyama Prefecture, although the use has been reported previously in several local histories published in Japanese language. The wild food plants identified in this study, along with their Japanese common names, food types, parts used, common uses, and number of reports, are listed in Table 1.

Table 1 A list of wild food plants identified in the study

Overall, Asteraceae (643 reports) was the most frequently reported family, followed by Poaceae (320), Araliaceae (239), Apiaceae (227), and Dennstaedtiaceae (199). The most species-rich family was Asteraceae (29 species), followed by Rosaceae (28), Poaceae (17), Apiaceae (11), Ericaceae (10), and Fabaceae (10). Of the Asteraceae and Poaceae, which had the largest number of reports and species were observed, all 29 species of Asteraceae were used as either vegetables or binders. Of the 17 species of Poaceae, 14 were identified as various types of bamboo, with the shoots used as vegetables and other species were consumed as raw snacks mainly by children. The high number of reports of Araliaceae and Apiaceae is due to the presence of species with a high number of reports, such as Aralia cordata (121 reports), A. elata (93) of Araliaceae, and Oenanthe javanica (183) of Apiaceae. The 299 reports of Dennstaedtiaceae are due to frequent reports of the use of one species, Pteridium latiusculum (warabi bracken).

Table 2 lists the species with more than 100 use reports in all Japanese regions. Among the 278 study sites, Petasites japonicus was used in 78%, Artemisia princeps in 75%, Pteridium latiusculum in 72%, Osmunda japonica in 58%, Oenanthe javanica in 50%, Castanea crenata in 44%, and Aralia cordata in 44%. All of these plants were eaten as vegetables except A. princeps, which was used as a binder. All seven species are still commonly consumed at present and are also found in both cultivated and wild forms. These are available for purchase at supermarkets and other retail outlets, and products that have been processed to facilitate consumption are also on the market. Of particular note is the cultivation of Aralia cordata (udo) and Oenanthe javanica (seri), with numerous cultivated varieties now in existence. While wild udo is frequently consumed as a vegetable, primarily for its shoots and leaves, cultivated udo is cultivated in a manner that blanches the stems, making them the primary edible portion. It is noteworthy that these cultivated species are classified and designated as sansai (mountain vegetables). On the other hand, the majority of species were sparsely reported. Eighty-three species (31% of the total taxa) were reported only once, 38 (14%) were reported twice, and 33 (12%) were reported three times.

Table 2 List of wild species traditionally used as food in Japan with more than 100 reports

In comparison with the use of wild food plants in South Korea, where the flora and climate are similar to Japan, there is a commonality in the use of Asteraceae as vegetables and binders. Conversely, the larger number of reports and species of Poaceae can be regarded as distinctive to Japan. Previous researches conducted in South Korea indicate that Poaceae does not represent a significant proportion of species or reported uses [27, 29, 30] while a study conducted on Jeju Island in South Korea has revealed that the majority of reported Poaceae are wild millets and other seeds, a finding that differs from that observed in this study [28]. On the other hand, seven species with over 100 reported uses, as outlined in Table 2, are also commonly consumed in South Korea.

Figure 2 shows choropleth maps of Japan showing the numbers of wild food plant reports (a) and species (b) in each prefecture. Gifu Prefecture in the Chubu region had the greatest number of species (71 species), followed by Okayama (62), Niigata (61), Hiroshima (57), and Shizuoka (55) (Fig. 2a). Concerning the number of reports, Gifu also had the highest number of reports (134 reports), followed by Niigata (123), Akita (120), Nagano (116), and Aomori (106) (Fig. 2b). The areas with the lowest use of wild species in terms of numbers of both reports and species were urban and coastal regions. In coastal areas, the uses of geographically distinctive wild species, including Farfugium japonicum, Glehnia littoralis and Tetragonia tetragonoides, were reported. However, the overall number of reports and species identified was comparatively lower than in other regions.

Fig. 2

The number of reports and species of wild food plants used in each prefecture

In previous studies, regional differences in the use of wild food plants in Japan have been discussed according to different forest zones [62, 63]. Several studies have suggested that the gathering and consumption of wild food plants and mushrooms has been more active in deciduous broad-leaved forests (or beech (Fagus crenata) forest zones in Japanese terminology), which primarily cover eastern Japan, especially in the heavy snowfall area from the Tohoku to Chubu regions, than in evergreen broad-leaved forests (or lucidophyllous forest zones), which primarily cover western Japan [35, 38, 64, 65]. As the number of study sites in each prefecture varies, the frequency and diversity of wild food plant use among prefectures are not comparable comprehensively with those in this study alone. Nevertheless, the findings of this study do not contradict those of previous studies.

All of the species listed in Table 2 were widely used throughout the country, with no regional differences. On the other hand, some species were used only in limited areas. For example, all of the 33 reports of Castanopsis sieboldii or C. cuspidata which seeds were eaten, were from regions west from Chiba prefecture, and all 27 reports of Clerodendrum trichotomum, which is used as a vegetable for its shoots and leaves, were from Shizuoka to the west. Castanopsis sieboldii and C. cuspidata are representative component of the evergreen broad-leaved forests (or lucidophyllous forest zones), while Clerodendrum trichotomum grows throughout Japan, from Hokkaido to Okinawa. A previous study focusing on the differences in the use of wild plants in eastern and western Japan has indicated that, in addition to species commonly used throughout Japan, eastern Japan is characterized by the use of species that grow in the forest understory, such as Onoclea struthiopteris, while western Japan is characterized by the use of plants found in close proximity to human settlements, such as Equisetum arvense [35]. Thus, the comparison of the number of reports and types of species used in different regions may be due to cultural reasons such as regional history and interaction with other regions, in addition to the relationship with the forest zone as pointed out in previous studies. Further studies that consider species- and region-specific backgrounds will be required in order to gain a better understanding of these regional differences.

Food category

Among the 9 food categories that were considered, vegetables were the largest group with 146 species, followed by dessert fruits with 78, beverages with 23, and snacks with 19 (Fig. 3).

Fig. 3

The percentage of species in each food category (n = 268)

The uses of most species (219 species, 82% of the total species) were limited to only one category, while 42 species were used for two categories, and 6 species were used for 3 categories. Only one species (Vitis coignetiae) was used in four categories: binders, beverages, dessert fruits, and other food types. The young leaves were used as binders in the production of mochi cakes. The infructescences were eaten raw as dessert fruits and were also used to make various beverages, such as juice, homemade liqueurs, and wine. Young fruits and exudates from vines were used in the production of agar jelly called tokoroten, and fruits were used to make local fermented foods such as lactic fermented vegetables.

Vegetables

Wild vegetables are generally called sansai (mountain vegetables) in Japan. As mentioned, the term sansai is believed to have been used since approximately 1960 [40]. The folk nomenclature of wild vegetables varied across different regions. For example, they were referred to as aomono (green/blue things), yama no mono (mountain things), okazu no kusa (grasses for side-dishes) and so forth. Aomono, which can be directly translated as ‘blue things’, is a common name for vegetables in general and was used in the case of wild vegetables such as yama no aomono (blue things of mountains).

The most represented families for vegetables were Asteraceae (24 species), followed by Poaceae (15), Apiaceae (11), and Brassicaceae (8) (Fig. 4a). These plants were eaten in various ways, including aemono (boiled and dressed with seasonings) and nimono (simmered dishes). Some vegetables consumed raw included those used in small quantities for flavoring and seasoning, such as Allium schoenoprasum and Zanthoxylum piperitum. Some species of Dioscorea, including D. polystachya and D. japonica, were also consumed raw in the form of grated roots, which were used in the preparation of tororo. Pickling was also a common method of cooking and preservation, utilizing a variety of ingredients, including salt, miso, sake lees and rice bran. As the majority of the species were collected during the spring season, these pickles were consumed as preserved food and were valuable foodstuffs during the winter months when vegetables were scarce.

Fig. 4

Botanical families with the greatest number of species used for the four major food categories. Percentages of botanical families for a vegetables (n = 146), b dessert fruit (n = 78), c beverages (n = 23), and d snacks (n = 19)

Other methods of preservation were employed, such as sun drying, salting and simmering down with soy sauce and sugar, known as tsukudani. Some plants, such as Aster yomena and Cirsium spp., were incorporated into rice dishes, including porridge. These vegetables contribute to the overall texture and flavor while also increasing the volume of the dishes. The ingredients used to increase the volume of rice-based dishes are referred to as "kate" or “katemono”. Historically, these were regarded as famine foods [66]. The use of plants to increase the volume of rice dishes has been similarly reported in other parts of Asia, for example, the use of the roots of Dioscorea bulbifera in Thailand [19].

The most common parts used as vegetables were shoots (61 species), which represent nearly half of the species used as vegetables. This was followed by leaves, unspecified aerial parts (both 33 species), roots (19) and stems (18). Five species of inflorescences were used as vegetables, with Petasites japonicus being the most commonly consumed throughout the country. The young flower buds are called fukinoto and are consumed in a variety of ways, including as tempura and cooked with miso. The fukinoto was described as a plant that sprouts first in spring and heralds the arrival of spring at several study sites. Other species whose inflorescences were eaten as vegetables include Wisteria spp. and Erythronium japonicum. Propagules of 3 species were used as vegetables during autumn.

The propagules are called mukago in Japanese, and two species of mukago yams (Dioscorea japonica and D. polystachya) were commonly eaten. They were eaten by roasting, boiling or as the kate ingredients as mentioned previously. The propagules of Elatostema involucratum were also eaten, although this was limited to one report. The leaves of these plants were removed, and only the stems with propagules were marinated in miso paste. They continue to be consumed in modern times in the northern part of Japan, such as Akita Prefecture. Due to their rarity, they are also used as a premium ingredient in traditional high-end Japanese restaurants such as ryotei, and have been employed as an accent as part of innovative dishes in non-Japanese restaurants such as Italian and French due to their distinctive texture.

These results are consistent with previous studies from other parts of Asia, such as in Thailand, Laos, and China, which demonstrated a preference for shoots and leaves [15,16,17, 19], also known as herbophilia [6]. However, this study was characterized by the fact that ferns such as Pteridium latiusculum, Osmunda japonica, and Onoclea struthiopteris were also frequently consumed as vegetables in Japan. Studies from South Korea have indicated both similarities and differences between the two countries. The cooked shoots of species from the Asteraceae family have been frequently consumed as vegetables during the spring season in both Japan and South Korea [27, 28, 30]. The findings of the present study were consistent with those previously reported from South Korea in terms of the plant taxa and part used, the preparation status (i.e., cooked or uncooked), and the season of use (i.e., spring). As mentioned earlier, there was also a notable difference in the use of bamboo shoots, with Japan demonstrating a higher frequency and diversity of usage compared to South Korea.

Dessert fruits

In total, there were 78 species of wild plants eaten as dessert fruits, of which almost one-third of the dessert fruits belonged to the Rosaceae family, followed by Ericaceae (8), Elaeagnaceae (4), and Rhamnaceae (4) (Fig. 4b). The most popular wild fruit was Akebia spp. (A. squinata and A. trifoliata). Their arils were eaten raw sometime as children’s snacks. Other parts of Akebia were also consumed as vegetables and tea. The stems and buds were consumed as tea and vegetables, while the pericarps were eaten as vegetables in various ways, such as pickled and stir-fried. The second most popular wild fruit was Rubus spp. As mentioned in the Methods section, wild strawberries are called noichigo (wild strawberry) or kiichigo (tree strawberry), and there are more than 30 wild Rubus species in Japan, including R. crataegifolius, R. parvifolius and R. sieboldii. Their infructescences were eaten raw, in many cases as children’s snacks. Boiled or pickled fruits were also eaten in some cases. For example, fruits of Pyrus pyrifolia were eaten mostly raw, but in some areas, they were boiled for consumption. There was also a record of fruits of Vaccinium oxycoccos being pickled in salt and then sprinkled with sugar and eaten with green tea in the mountainous Oze area in Gunma Prefecture.

Beverages

There were 23 species used as beverages, including both alcoholic and nonalcoholic drinks (Fig. 4c). Alcoholic beverages were of two types: so-called wines, in which infructescences were naturally fermented, and so-called liqueurs, in which plants were soaked in spirits such as shochu. Nonalcoholic beverages included tea and juice.

Sixteen species were used as teas, including five species of Fabaceae, namely Vicia bungei and Wisteria spp. Most of them used their aerial parts, such as leaves, shoots and inflorescence, and were processed by steaming, drying or roasting. On the other hand, one study reported that roots were used as tea. The roots of Imperata cylindrica were sun-dried and drunk as tea, which was favored by elderly people because it improves the production of urine.

Following the tea, seven species were used to make liqueurs. Most of them use infructescences, except for the species Geranium thunbergii, whose aerial parts were used.² In contrast, only two species (Vitis coignetiae and V. ficifolia) were used for making wine. Although the berries were used, the method of making wine exhibited slight regional variations, including the collection of berries when they were ripe or after frost or fermentation with or without sugar.

Snacks

Snacks are plants eaten between meals, excluding dessert fruits and nuts. In total, 19 species were eaten as snacks, including 4 from Poaceae and three each from Ericaceae and Polygonaceae (Fig. 4d). Many of these snacks were eaten raw as children's snacks. Many were aerial parts, such as shoots, leaves, stems, and flowers, and there were many records of children foraging freely for snacks in the fields and mountains.

Among the snacks, many sour-tasting plants, such as Rumex japonicus and Japanese knotweed (Reynoutria japonica), were eaten raw. They were sometimes eaten with salt on the spot of foraging. Similarly, children eating these acidic-tasting species have been documented in various European countries, including Spain, Sweden, and Poland [8]. There were other snacks that have a sweet taste, such as common grass (Imperata cylindrica), whose young ears and other parts were eaten; nectar from some flowers, such as Azalea; and the roots of Cinnamomum sieboldii. Another interesting finding was that leaf galls of Rhododendron spp. (Azalea gall) were eaten raw as snacks, although this finding was limited to three reports. Azalea leaf galls are caused by fungi, including Exobasidium spp. [67], and locally called mochi (rice cake), the disease is called mochi disease. There have been reports of the use of plant galls in other parts of the world, including as folk medicine and for dyeing [68,69,70].

Starches

The 17 species used as starches were largely divided into those that use roots and those that use seeds. The most common family associated with the roots was Liliaceae (4 species), whereas the most common family associated with the seeds was Fagaceae (4 species), which included 3 Quercus spp. (Q. acuta, Q. gilva, and Q. glauca). Various techniques were used to extract starches, such as pounding, grating, soaking in water and strain. These extracted starches were used for making rice cakes, noodles, porridges and jelly type foods.

Two toxic plants (Lycoris radiata and Cycas revoluta) were included in this category. Although it was limited to only one report, bulbs of L. radiata were used for making starches. L. radiata contains lycorine, which is commonly found in the Amaryllidaceae [71]. People were aware of this toxicity; therefore, they took a long time to remove the poison by being exposed to water repeatedly over a long period of time. Another poisonous plant was Cycas revoluta. Their seeds and stems were used for extracting starches, particularly from the Ryukyu and Amami Islands of southern Japan. Like the use of L. radiata, to remove toxins, including cycasin, the plant parts used were exposed to water repeatedly over time. In some areas, people fermented them, and some reported the infestation of maggots as a sign of detoxification.

Binders

Plants used to combine food ingredients are categorized as binders or “tsunagi” in Japanese. They were mostly used for rice cakes (mochi and dango) and sometimes for soba (buckwheat noodles). Among the 13 species used in this category, there were 8 species of Asteraceae, including two Artemisia spp. (A. princeps and indica) and 3 Synurus spp. (S. pungens, deltoides and excelsus). Young leaves and shoots of these species were boiled and added to food, and their trichomes and fibers contribute to the binding of other ingredients. In addition, some binder plants, such as Artemisia spp. and Pseudognaphalium affine, also contribute to the aroma or color of the prepared food. Although it was limited to two reports, the bark and cortex of red pine (Pinus densiflora) were used to make rice cakes called matsukawa mochi (pine skin rice cakes). Compared with other parts of the world, A. spp. and other species have been used as ingredients for rice cakes in China and South Korea [72,73,74]. Some research has also indicated that the use of P. affine for mochi in Japan was originally introduced from China and was later replaced by the use of Arstemisiaspp. as an alternative to P. affine [75].

Nuts

Among the 13 species consumed as nuts, Fagaceae presented the greatest number of species (6 species). Although most species were tree plants, the seeds of 3 species of aquatic plants were also eaten as nuts (Trapa natans var. Bispinosa, Nelumbo nucifera, and Euryale feroxe). These nuts were eaten raw, roasted, or boiled and sometimes as snacks.

Oils/fats

There were only 3 species used for oils/fats (Terreya nucifera, Camellia japonica, and C. Sasanqua). Oils were extracted from seeds of these species. Among the three species, C. japonica was the most frequently reported, although its use was limited to only 6 reports in western Japan, particularly in the Kyushu region. The other two species were reported only once each. These oils were considered valuable and were sometimes sold and given as gifts.

Other food types

This category included the 13 species used for coloring, flavoring, fermented foods, or algae jelly making. For coloring and flavoring, for example, Gardenia jasminoides was used to add yellow color to food, including rice cakes and pickled vegetables. Another example is chick weeds (Stellaria media). In addition to their use as vegetables, they were also used for coloring and flavoring. In the Nasu area of Tochigi Prefecture, their aerial parts were used along with shiso leaves (Perilla frutescens) to provide sourness and better color when pickling plums (Prunus mume).

There were 8 species used for fermented foods, and their reports were all regionally specific. Some species (Humulus cordifolius and Equisetum arvense) were added when alcoholic beverages such as rice wine were made, since they were considered to accelerate fermentation in the Tohoku region. In Nagano Prefecture, juices made from infructescences of 3 species (Malus toringo, Pyrus pyrifolia, and Cycas revoluta) were used for unsalted lactic-fermented pickles called sunki. These compounds are called “sources” or “essences” of sunki pickles and are believed to contribute to pH control and the production of lactic acid, etc. [76]. As mentioned previously, the use of Cycas revoluta was limited to only southern islands. On Amami islands, seeds of C. revoluta were also used to make koji molds (fermentation starters) for making fermented soy bean paste, miso. The production of sunki pickles in Nagano and miso of C. revoluta in Amami islands persists to the present day, and each is acknowledged as a local delicacy, with both also available for purchase including online.

Two species (Oxalis corniculata and Vitis coignetiae) were used to make tokoroten, jelly noodles made from red algae, including Gelidium amansii. The use of O. corniculata was reported only once in Ishikawa Prefecture, while there were 3 reports of the use of V. coignatiae in the Tohoku and Hokkaido regions. The parts used and how to use them differed from each other. Aerial parts of O. corniculate or unripen fruits of V. coignetiae were used when boiling red algae instead of vinegar. These compounds are considered to help extract agarose from red algae [77]. Sour-tasting saps from vines of V. coignetiae were used after red algae were boiled, but they were used to curdle the agar jelly. Thus, these sour plants were used to extract or solidify the jelly.

Toxic plants

There were several reports of the use of toxic plants, although the type and degree of toxicity vary. For example, species containing carcinogens were eaten. As mentioned, bracken (Pteridium latiusculum) is commonly eaten throughout Japan, with shoots being eaten as vegetables and bracken starch extracted from the roots. Bracken contains a carcinogen called ptaquiloside [78]. Another plant that contains carcinogens is Cycas revoluta. Stems and seeds of C. revoluta were used to make starch and fermentation starters; however, C. revoluta contains a carcinogen called cycasin, which is found in other cycads [79].

Alkaloid-containing species were also consumed. For example, rhizomes of Dioscorea spp. (specifically D. tokoro) were boiled and consumed. Their rhizomes contain dioscin, a type of saponin that is commonly found in Dioscorea spp. [80]. For example, D. tokoro was initially reported to have a very bitter taste but became palatable once people became accustomed to it in Saga Prefecture. Interestingly, in two of the five use reports of D. tokoro, they were also used as an offering. The use as offerings to the gods has been reported in several places in Japan [41]. Another alkaloid-containing species consumed was Lycoris radiata for starch from its bulbs, as mentioned previously.

One of the most toxic plants eaten was the lacquer tree (Toxicodendron vernicifluum), which widely grows in China, South Korea and Japan. In Asia, sap is used as a lacquer, but it contains an allergen called urushiol [81]. In Miyagi and Ibaraki prefectures, their shoots were consumed as vegetables. In Miyagi, older individuals liked to consume shoots because of their soft texture, whereas in Ibaraki, they were regarded as tasty but potentially irritating food, with the decision to consume them dependent on the individual. It has been reported that individuals engaged in lacquer production, such as artisans, adhere to the custom of eating lacquer plants as a means of reducing their susceptibility to lacquer rash in Japan [82]. However, the two regions reported in this study were not lacquer-producing areas and therefore cannot be relevant to this case of lacquer eating for immunity. On the other hand, the consumption of leafy shoots of T. vernicifluum as vegetables has been reported among ethnic minority groups in China, such as Lemo and Dulong in Yunnan Province and Yi in Sichuan Province [22, 83, 84]. To understand the food use of lacquers in Japan, it is necessary to consider the food use of lacquers in the wider context of Asia.

Processing techniques

The majority of plants, particularly vegetables, were consumed primarily in cooked form. A range of other processing techniques were also employed. In particular, almost 300 reports of akunuki, a food processing technique used to remove aku, which are unpalatable and undesirable substances or tastes such as harshness and astringency, existed. The akunuki methods include the followings: (1) the use of various ingredients, such as ash, rice water (water used to wash rice), rice bran, baking soda, vinegar, and camellia leaves; (2) prolonged soaking in water; (3) prolonged burial in soil; (4) fermentation; and (5)a combination of these methods. Some of these techniques are capable of removing not only unpleasant tastes but also toxic substances from wild species.

The most common akunuki method was the use of ashes (179 reports). In many cases, the plant parts were soaked in water with ash for a long time or boiled. Among the species that were pretreated with ashes, warabi bracken (Pteridium latiusculum) was reported most frequently (80 reports), followed by Artemisia princeps (31), Osmunda japonica (28) and Aesculus turbinata (22). These reports included detailed descriptions of the specific types of ash to be used, for example, ash from stoves and hearths, rice straw ash and wood ash. There were several reports of the use of specific types of ash, particularly in the pretreatment of Aesculus turbinata seeds when they were mixed with glutinous rice to produce rice cakes (tochi mochi). Among the 22 reports, more than half described specific types of ashes to be used, including those of hardwoods, mainly Quercus spp. The use of ash, which is alkaline, for plant detoxification is a well-known traditional method involving pH control [85]. The reason for the use of hardwood ashes, such as those derived from Quercus spp., is likely due to the pronounced alkalinity of these ashes, which has a greater impact on detoxification [86].

The second most common method used for akunuki was the use of rice bran (58 reports). The plant parts were boiled in water with rice bran or, alternatively, left over water after rising rice was used. This method is commonly employed for the preparation of a variety of bamboo shoots. The use of rice bran is likely to facilitate the adsorption of undesired substances [85]. In other Asian countries where bamboo shoots are widely consumed, boiling in water or saltwater is the predominant pretreatment method [87]. A previous study suggested that the method of using rice bran is a relatively recent phenomenon that emerged after the late Meiji period (1868–1912) [88].

Medicinal plants

Previous studies have demonstrated a blurred boundary between food and medicine in the use of wild plants [89, 90]. This study also identified 28 plant species that were used for food, medicinal and health-promoting purposes (Table 3). These plants were consumed for the treatment of various health conditions, including detoxification, deworming, cough, fever, tinnitus, and dizziness. Some of them were consumed specifically by infants, children, pregnant women, postpartum women and elderly individuals. The most frequently occurring species were those belonging to the Asteraceae family (5 species), followed by those of Lamiaceae (3 species). The species that were consumed as medicines included those that were commonly eaten as food throughout the country. For example, there were three reports of juice extracted from buds or roots of Petasites japonicus being given to newborns to detoxify the embryotoxic (taidoku)[91, 92].³ Another example was Osmunda japonica. In the Tohoku region, they were believed to be beneficial for consumption after childbirth, with the aim of improving blood circulation or cleansing blood. Conversely, in Niigata Prefecture, eating them after birth was prohibited because they believed that they could cause blood to become “rough”. There were also six species, including Artemisia princeps, that were consumed as herbal teas, which are generally regarded as beneficial for the body.

Table 3 A list of species consumed as food as well as for medicinal and health-related purposes

Male and female plants

There were 6 reports on the uses of male and female plants of the 5 species. In Gifu Prefecture, stems of Reynoutria japonica were eaten raw as snacks with salt. The stems of the female plants were preferred because they were thicker, softer, and tasted sour, whereas the stems of the male plants were thinner and harder.

Additionally, some reports indicate that plant sex determines whether a plant is used. For example, in Amami Ōshima Island of Kagoshima Prefecture, stems of Cycas revoluta were processed and used as starches. Only male plants were selected for starch extraction, as male plants were considered to store more starch. Another example involves 2 species of Liliaceae (Cardiocrinum cordatum and Lilium auratum var. auratum), where the roots of the female plants were only selected for starch extraction. Reynoutria japonica and Cycas revoluta are dioecious plant species, whereas Lilium auratum var. auratum and Cardiocrinum cordatum are not.

Thus, preferences for texture and flavor and whether to use plants were determined according to the sex of the plants. However, how male and female plants were locally identified for some of these species was not described in the literature. As there are only a few studies on traditional knowledge of plant dioecy and the folk concepts of plant sex, further research is needed on the local perceptions of plant sex, as suggested by previous studies [93, 94].

Cultural significance of wild species

The results indicated that many of wild food plants hold cultural significance in Japan. These include their use as (1) essential foodstuffs for various special occasions, (2) cash plants for income generation, (3) their presence as ingredients for local cuisines and in relation to local identity, and (4) precious and valuable foods. There were 64 reports citing the use of wild food plants for special occasions such as New Year celebrations, Bon festivals, Shinto and Buddhist rituals, local rituals, Risshun, the first day of spring in the Chinese lunar calendar and Gosekku, the five seasonal festivals. The most commonly used species for special occasions was zenmai (Osmunda japonica), which was reported as an essential food ingredient for several dishes, including a simmered dish (nimono) served during special occasions as Buddhist memorial services throughout the country.

Secondly, there were reports of plants being collected for selling purposes. Of these, chestnuts (Castanea crenata) and zenmai (O. japonica) were each mentioned in six reports. In some areas, traders came to the area to buy wild species including chestnuts in Akita prefecture and zenmai fern in Tokushima prefecture. There was a report that people accumulated enough money to buy a mountain by selling warabi (Pteridium latiusculum) in Hyogo prefecture. The trade in wild food plants persists to the present day. In addition to being transported to markets, foraged wild food plants are also sold as souvenirs at local outlets, including roadside stations called michi-no-eki as well as in community-powered marketplaces on the Internet for smaller-scale trading.

Furthermore, there were reports indicating that wild food plants were associated with local identity. For instance, they were identified as a vital component of regional cuisine, or as a highly preferred food among the local population, with some species such as Hasteola robusta and Smilax riparia even featured in folk songs in Akita prefecture. In the present era, the dishes with wild food species represent a further aspect of the regional cuisine as they are based on the specific utilization, culinary techniques, and methods of preparation and processing of wild food plants that are distinctive to the region.

Some wild food plants were also described as being precious and valuable. In addition to the direct statement, for example, horse chestnuts (Aesculus turbinata) in Niigata were a luxury item and not regularly eaten, there were indirect descriptions which suggests that some of the wild food plants were perceived as precious foods. In Yamagata Prefecture, if you were given bracken fern (Pteridium latiusculum), you have to thank many times, and that in Niigata Prefecture, people were considered to be rude if they did not praise a long piece of zenmai (O. japonica) served at a celebration.

Taste and flavor

Taste and flavor and their appreciation have also been considered to be a part of cultural significance of wild food species [95]. There were a number of descriptions pertaining to the taste and flavor of wild species. These can be broadly classified into those pertaining to flavor, texture, and taste. Flavors were described as being of good quality, specific to wild species, in the spring, with all of them being perceived as positive. For example, in Akita, Hasteola robusta was carefully cooked as tempura to retain its distinctive aroma, which is considered important.

There were several reports about texture, including the sliminess of Elatostema involucratum, the crispness of Astilbe rubra, and the stickiness and gooeyness of Lilium auratum var. auratum. These attributes were all regarded as positive. In terms of taste, wild species were often described as having a distinctive and slightly bitter taste, which were also perceived as good. This was exemplified in the preparation of seeds of Aesculus turbinata and bulbs of L. auratum var. auratum, where some described taking care not to lose all of the bitterness. There were also nine reports that the taste of wild species was better than that of cultivated or purchased species or those grown in proximity to their residences. Examples of these include udo (Aralia cordata), butterbur (Petasites japonicus), chestnut (Castanea crenata) and yam (Dioscorea japonica). Thus, wild food plants were considered a source of enjoyment through their unique tastes and flavors in Japan.

Several previous studies have shown that wild vegetables were appreciated and preferred because of their tastes, for example, in southern Italy, Thailand, Himalaya and Japan [44, 96,97,98,99]. In the field of Japanese folklore, studies have examined the unique taste and cleansing properties of wild vegetables. For instance, there is a dialect word, 'kidoi', which is used to describe the nature of wild food plants, particularly in Tohoku region [41]. The term denotes a harsh, bitter, and astringent quality, including a distinctive olfactory sensation characterized by a potent and pungent flavor. In these areas, this quality of spring wild vegetables is perceived as a means of cleansing and detoxifying the body from the impurities and fatigue accumulated during the winter months.

While no expressions were identified as pertaining only to the taste of wild species such as kidoi in this study, the taste and flavor of wild species were observed to be linked to the arrival of spring. In many areas, these were regarded as spring tastes that people look forward to, particularly in regions where winter is long. It may be of interest to note that species mentioned as having a taste associated with spring include Adenophora triphylla var. japonica, Capsella bursa-pastoris and Oenanthe javanica, which were used as wild vegetables. All species have been previously reported for their antioxidant and phytochemical properties [73, 100, 101]. Given that previous studies have suggested how the specific tastes and flavors of wild species are associated with their health properties [96, 102], it seems plausible to suggest that these perceptions of the spring taste of wild species Japan are likely to be related to their health properties.

Use of rare species

There were few reports on the use of threatened species according to their current conservation status. Among the 2163 species of vascular plants listed on the 2020 Japanese Red List [103], the following four species were used approximately 1930: Platycodon grandifloras, prickly waterlily (Euryale ferox), and bird’s nest fern (Asplenium antiquum), which are listed as endangered, and Cinnamomum sieboldii, which is listed as near threatened. The roots of P. grandifloras were pickled in plum vinegar and were traditionally consumed in Hiroshima Prefecture. They are also used as a cough medicine, although their taste was not very tasty. There were 2 reports about the use of Euryale ferox. The cooked stems were eaten as vegetables, whereas the roasted or boiled seeds were eaten as snacks. Additionally, dried and ground seeds were used as starches to make dumplings (dango). Asplenium antiquum was reported once in Ishigaki city in Okinawa, where the shoots were used as vegetables in simmered or dressed dishes. Cinnamomum sieboldii was reported twice. The roots were eaten raw as snacks for the children.

Conclusions

This study examined Japan's largest food culture database and reviewed the food use of wild plants in the early Showa period (1926–1989). At least 268 taxa of plants belonging to 88 families were used to make food and beverages in Japan. Asteraceae was the most frequently reported and most species-rich family. The majority of species was documented in only a limited number of reports, and the number of species used at the national level was limited. In other words, each region and locality had its own distinctive culinary traditions involving wild food species. A comparison with those of previous studies on wild species used in other Asian regions revealed a similar preference for vegetables, namely shoots and leaves. However, notably, in Japan, ferns and bamboos were also consumed in considerable quantities. Furthermore, there were some other similarities with other Asian regions, including folk uses of plants such as binder plants and kate plants and the consumption of toxic plants (lacquers). Conversely, further elucidation is clearly needed with respect to certain matters, including the perception of plant sex, the relationship between the consumption of lacquer and immunity, and the relationships between diverse ash components and detoxification techniques.

At present, data on the use of wild food plants in Japan are largely confined to specific plant species and select regions. Consequently, there is a lack of comprehensive understandings of the current use of wild food plants over Japan. While there are reports indicating a decline in the use of wild food plants, there are also emerging trends such as the practice of wild vegetable gathering for recreational purposes and the formation of wild food plants gathering groups in urban areas. The situation surrounding wild food species in Japan is evolving rapidly, with an increase in the number of popular books, illustrated books and online resources, as well as reports of species that were previously only consumed in specific regions now being incorporated into the diet. This study provided insight into the use of wild food plants which once existed in Japan around 1930. To gain a comprehensive understanding of the changes that have occurred and the current status of wild food plant use in Japan, it is essential to conduct interdisciplinary research. The study also revealed that wild food plants are not only natural resource or source of nutrition, but that their use is also deeply rooted in culture. It is therefore evident that further ethnobotanical research is needed, both in the form of an examination of ethnographic records and in the field, to gain a deeper understanding of the cultural use of wild food plants in Japan.