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.Footnote 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].Footnote 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 purposesMale 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 rit