Ethnobotanical study on medicinal dietary plants used by the Yi people in southeastern Yunnan, China

Background With a population of more than 5 million, Yi is the largest of the 25 ethnic groups in Yunnan Province, China. Yi people tend to live in mountainous areas, and their culture includes a unique dietary system for treating illnesses and protecting people against them. Medicinal plants occupy an essential place in the Yi diet because they play a key role in health and the prevention and treatment of diseases. The objectives of this paper were to document the medicinal dietary plants and the traditional knowledge associated with them and describes this paper adequately. Field investigations were carried out in six villages in Mile County, Honghe Hani and Yi Autonomous Prefecture, Yunnan, from July 2017 to May 2018. Information was collected using participatory rural appraisal (PRA), direct observation, semi-structured interviews, key informant interviews, individual discussions, focus group discussions, and questionnaires.

the conservation and sustainable use of these plant resources and can contribute to the protection of the Yi food culture and traditional medicine in Mile. In addition, this information provides a basis for the development and utilization of Yi ethnic medicine and health products.

Background
There are many overlaps between medicine and food, and dietary products can simultaneously be food and medicine [1]. The concept of "medicinal dietary" is based on ancient lore about food, and medicine discovery in ancient times, which reflected the edibility and medicinal function of certain plants. In fact, many plants in local food cultures have therapeutic value. The idea of "food as medicine" has existed in China since ancient times. In recent years, with the general improvement in people's living standards, knowledge about dietary hygiene and nutrition has become more widespread. In the world, People are paying more attention to health care, health preservation, and are advocating natural cures. In western countries, some people propose "kitchen instead of pharmacy" and "food instead of medicine" [2].
In the 1930s, there was a saying in China that "food and medicine have the same origin". The first mainstream herbology monograph in China, the Holy Husbandman's Classic on Roots and Herbs recorded many medicinal dietary plants. Since 1985, more than 10 food therapy books a year have been published in China [3]. However, the study of medicinal diets used by indigenous communities in China has been largely neglected. Yi, one of the most ancient ethnic groups in Southwest China [4], is the sixth largest ethnic minority [5], and is mainly distributed in Yunnan, Guizhou, Sichuan, and Guangxi provinces in southwest China, with a population of approximately 8.71 million. Around 61% of the Yi people live in Yunnan Province [6]. Two autonomous prefectures, Chuxiong and Honghe, and another 15 autonomous counties, including Nanjian, Luquan, and Shilin, are the primary locations for the Yi people in Yunnan Province. The rise in Yi medicine in the southwest can be traced to the Eastern Han Dynasty, 1800 years ago [4]. In the long struggle against disease and harsh environments, a specific system of diet and medicine was developed by the Yi [7]. For instance, many medicinal plants are used not only for essential components of the daily diet but also play an important role in health care and disease prevention under conditions of limited medical resources [8][9][10][11][12][13]. Xian Yao Ching of Yi ethnicity wrote during the Qing Dynasty (AC 1636) that all vegetables and plants could be used as medicinal materials. Plants such as Amomum tsaoko, Zingiber officinale, and Piper nigrum L. were reported to show therapeutic efficacy. Furthermore all plants, animals, livestock materials, and grains used as medicines could be administered in combination with each other to improve curative effects [14]. Previously, some records about the medicinal plants of the Yi have been documented in publications such as Yi medicines [14], Yi herb medicines [15], Theory and application of Yi medicine [16] and Yi medicines of Chinese [17].

Study area
Honghe Hani and Yi autonomous prefecture is located in the southeastern Yunnan Province, China, with Wenshan to the east, Kunming to the north, Yuxi to the west, and Vietnam to south [21]. Mile Field studies were carried out during three visits from July 2017 to May 2018. This study was carried out following the guidelines of the International Society of Ethnobiology Code of Ethics (http: //www.ethnobiology.net) [23] and the American Anthropological Association Code of Ethics (https://www.americananthro.org) [24]. Thirty-six key informants, who had considerable knowledge and experience regarding the use of medicinal dietary plants were selected for interviews, including eight healers. Most of them had acquired medical treatment skills and knowledge from their parents.
Ethnobotanical data were collected through participatory rural appraisal (PRA) [25], direct observation, semi-structured interviews, key informant interviews, individual discussions, focus group discussions, and questionnaires [26][27][28]. In the present study, the Yi names, local names, Latin names, edible parts, medicinal parts, preparation methods, and efficacy of the plants were recorded. Some information on Yi ethnic medicine and food culture was also recorded. The research focused exclusively on medicinal dietary plant use and knowledge. All interviews were conducted with the interviewee's consent. Generally, they were required to answer the following questions:  [33][34][35]. The formula for UV is Ui is the number of times cited by each informant for a certain medicinal dietary plant, while N is the total number of informants [35]. The frequency of utilization index (FUI) of medicinal dietary plant species was graded according to the frequency of consumption by local people. FUI can also reflect the degree of closeness between the medicinal dietary plant species and the local community [35].
The FUI scores range from 0 to 5 and vary according to the consumption frequency (Table 1) [35].  (2), lichens (1), and fungi (1) ( Table 2 and Table 3). Detailed information about these plants is displayed in   In the Mile area, 124 plant species were used as food and medicine, whereas the results of previous studies show that in Xishuangbanna and Jinfo, the number was lower [18,21]. The overlap between these areas is illustrated using a Venn diagram (Fig. 2).
Locally Important Plants Analyses to determine local importance

Uses of locally important plants
A. konjac is a popular food in the daily life of the Yi people. It contains a pharmacologically active heteropolysaccharide, konjac glucomannan (KGM), extracted from konjac tubers. KGM has the characteristics of water absorption, gelatinization, adhesiveness and low heat edible, so it is widely used in food processing, pharmaceuticals, and health-care products [36].
C. moschata is a daily food for local people and is made into all kinds of dishes like pumpkin pie, pumpkin soup, pumpkin porridge, and fried pumpkin (Fig. 3). Pumpkin seeds are believed to kill parasites and are eaten after peeling and frying. Children enjoy the crispy texture and find it much more acceptable to eat fried pumpkin seeds than to take medicine.

Preparation Of Medicinal Dietary Plants Medicinal preparation
The primary medicinal preparation method for plants recorded in the study was decoction, followed by stir-frying and eating fresh. However, 28 species required specific preparation methods (Table 2). The main cooking method for the plants documented in this survey was boiling, followed by stirfrying, and eating fresh. The study noted that three species, Pisum sativum, Pinus yunnanensis, and Esholtzia rugulosa, required specific cooking methods. These three plants are converted into konjac tofu, cakes, and tea, respectively. Another plant requiring special preparation is Linum usitatissimum.
Local Yi people like to eat the seed of L. usitatissimum as oil and seasoning, so the seed must be prepared through powdering and pressing.

Preparation For Toxic Plants
Generally, traditional preparation methods of medicinal plants are similar to those normally used in cooking; however, some poisonous plants need special preparation. Aconitum hemsleyanum is a highly toxic plant because it contains aconitine. The preparation process is strictly controlled to protect against the toxic effects. The specific cooking process is as follows: the water must be boiled completely, and then put into fresh aconitum root and lard, constantly boiled for at least 24 h. Keep adding boiling water to prevent the water evaporate, ensure food safety and prevent food poisoning.
Besides, people should stay in a warm room for one night after eating the concoction. This processing method is different from Kang's and Zhang's reported [37,38].

Plant Parts Used
The most frequently used edible parts are fruits, leaves, roots, flowers, tender shoots, seeds, and the whole plant (Fig. 4).

Medicinal Parts And Edible Parts Compared
Among the 124 plants documented in the study, 40 species had edible parts that were used for both food and medicine. In 82 species, however, the parts used for medicine and the parts used for food were different. For example, the tender shoot of Aralia chinensis can be eaten after frying or boiling, while a decoction of the bark and roots can tonify the liver and treat rheumatism. In Z. mays, the grain is eaten, while the corn silk has medicinal properties. It was observed that, through the longterm use of these plants, the Yi people had a very thorough understanding of the characteristics and effects of the various plant parts, and so made the best use of these resources. The preference for wild-collected leafy vegetables and fruits over underground plant parts for food seems to be common among diverse ethnic groups in Mile and might be due to the ease of collecting above-ground parts; see Fig. 4 and Table 2. The most frequently used medicinal parts of these plants are roots, and this may be due to the relatively high medicinal content.

Conditions Treated By Yi Medicinal Plants
The medicinal dietary plants used by the Yi people are diverse and contribute to the treatment of a number of disorders, such as cough, catarrh, rheumatism, swelling, kidney deficiency, spleen deficiency, gastric disease, and parasites (Table 5). These diseases are widespread among ethnic groups living in the mountains. Yi people are prone to rheumatism and respiratory diseases due to the humid air, and are often injured during hunting. Urinary tract and digestive system diseases are also frequent among the Yi. Modern Yi medicine developed from years of experience of environmental hazards and disease.

Medicinal And Edible Plants Worldwide
Currently, more than 80% of the world's population relies on traditional medicine for primary health care [26]. can protect the gastric mucosa and is a good treatment for dry skin. Thus P. utilis has great potential for development as a raw material for natural skin-care and health-care products [42].
Another medicinal dietary plant with economic potential is A. konjac. This is one of the materials used to make konjac tofu, which can be stir-fried with Chinese sauerkraut, or chicken, or used in a cold dish. The stem of A. konjac is used for detoxification and can treat detumescence, phlegm, bronchitis, and cough [43].
A popular local Mile plant with commercial potential is P. emblica. The flavor of the fruit is unique, with an initial sour taste and then a sweet taste. Yi people like to eat the bark. They remove the bark from the fresh trunk and scrape the endothelium with a ceramic implement or knife to obtain ribbonthin slices, which can be used in a cold dish or stir-fried with meat [33].
Apart from their use in food and medicine, many of the species in the study were put to multiple other uses. For example, many of them are used as ornamental plants or made into teas. Wild food plant species are abundant and diverse in Mile city, they provide food for the local people, and is also a source of income. People are paying more attention to food safety and preservation of health.
Medicinal dietary plants, because of their excellent beneficial effects in disease prevention and treatment, should be developed as health products or drugs [44].

Pharmacological Properties
Drugs derived from plants or their extracts have certain therapeutic properties. If antibiotics are replaced by suitable therapeutic agents, plants can play an important role in combating bacterial pathogens. In this section, we will analyze the pharmacological properties of the most utilized medicinal plant species to check their therapeutic efficacy. This is important because antibiotic resistance is an emerging global concern and research hotspot with respect to veterinary and human medicine.
The bulb of A. konjac is used to remove toxicity, to treat detumescence, to invigorate the stomach and to stop pain; in addition, it can treat bronchitis and persistent cough [45]. Pharmacological studies have shown that it has anti-microbial and anti-oxidation effects and lowers blood lipids and blood glucose. The fruits are rich in vitamin C and carotene, and the seeds are rich in fatty acids, phospholipids, and essential oils. The fruit, bark, and leaves contain tannins and can be used for treating diarrhea. Six polyphenolic compounds are obtained from P. emblica fruit juice.
The flowers of Camellia japonica can be used as medicine and have an astringent action, and the leaves can be used as a substitute for tea. The oil from the seeds contains 5 kinds of fatty acids and has an unsaturated fatty acid content of more than 80%. It also contains 8 kinds of mineral elements, such as iron, sodium, and magnesium, and can be used as a tonic. In addition, the plant contains flavonoids, polyphenols, and tea glycosides. Another plant with multiple medicinal uses is Pinus armandii. Local people use the shoots of P. armandii to treat rheumatic joint pain and traumatic injury. The seed kernels are used to treat the cough caused by lung heat (a syndrome in Chinese medicine) and habitual constipation, while the pollen is used to treat stomach and duodenalulcers. P.
armandii seeds have an oil content of 56.5%, which includes linoleic acid, oleic acid, palmitic acid, and arachidonic acid. In one study, the unsaturated fatty acids of P. armandii seeds had a significant inhibitory effect on hyperlipidemia and arteriosclerosis in mice [46].

Conservation Issues
With the rapid development of the economy and an accelerating loss of biological and cultural diversity, a large amount of traditional knowledge in minority nationalities is in danger of disappearing. Therefore, the documentation and evaluation of traditional knowledge related to plant diversity and the use and effects of medicinal food plants are crucial [47,48]. For example, plants such as D. delavayi, S. henryi, Adenophora stricta, and Codonopsis foetens are scarce wild resources.
Many precious plant resources that have the potential for future sustainable development are vanishing before they have even been discovered. The development of plant resources is necessary to maintain biological diversity and for the potential development of drugs and health-care products.
Meanwhile, the loss of traditional knowledge has been recognized as a development that has important negative effects on biological diversity conservation [49]. A reduction in plant diversity also leads to the extinction of the associated indigenous knowledge.  [50].
With the rapid development of the economy and the increased adoption of mainstream culture, the transfer of traditional knowledge between generations is disrupted. In addition, due to the excessive exploitation of wild plants, some of these resources have been exhausted. For example, it was very difficult to find A. hemsleyanum in the wild. Admittedly, over-exploitation of these resources has led to some degree of protection through cultivation. Artificial cultivation of Acanthopanax senticosus and Yunnan or in the country as a whole. In the future, we will conduct the relevant studies needed to obtain more comprehensive information. In future work, we will carry out relevant researches in order to obtain more comprehensive information. We will do more similar studies some years apart.

Acknowledgements
We are thankful to the local people for their assistance in the field investigations and for sharing their valuable knowledge.

Authors' contributions
XZH and SGL designed and conceived the study. XZH, JXS, YX, QSY, YJC, MYJ, YHL, YKL, HRL, ZZB and SGL performed the field survey. JXS and YX prepared the manuscript. XZH revised and finalized the manuscript. All authors read and approved the final manuscript.

Funding
This work was financially supported by the National Natural Science Foundation of China (NSFC No.

Availability of data and materials
All data generated or analyzed during this study are included in this published article (and its supplementary information files).

Ethics approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Competing interests
All the authors declare that there is no conflict of interest.