Ethnobotanical study on medicinal plants used by Mulam people in Guangxi, China

Background The Mulam are an ethnic group native to Guangxi, and nearly 80% of the Mulam population lives in Luocheng Mulam Autonomous County, northern Guangxi, southern China. They have accumulated rich medicinal folk knowledge through practice and experience in their long-term struggles with disease and the harsh natural environment. However, their traditional medicinal knowledge is threatened due to a lack of written records, conservative inheritance patterns, and rapid economic development. Therefore, the investigation and documentation of medicinal plants and their associated indigenous wisdom are necessary. Method Ethnobotanical data were collected from 12 villages and five communities in Luocheng County from January 2013 to April 2017. A total of 128 informants were interviewed through semistructured interviews, field observations, group discussions, and guided field walks. Quantitative indices such as use categories, preference ranking exercises, the informant consensus factor (ICF), and the fidelity level (FL) were used to evaluate the importance of medicinal plant species. Additionally, group discussions were conducted about the conservation of and threats to medicinal plants and traditional knowledge. Results A total of 456 medicinal plant species from 350 genera and 132 families were recorded and documented in our ethnobotanical investigation. Most of them (335 species, 73.47%) were obtained from wild habitats. Most of the documented species (246) were herbaceous (54%), followed by shrubs, with 76 species (17%), lianas, with 75 species (16%), and trees, with 59 species (13%). The most common method of administration was oral administration, which was used for 390 species (62.70%). The most common method of preparation was decoction (316 species, 54.11%). The plants were used to treat 312 human diseases in 12 disease categories, and most of the categories had a high ICF value. The highest ICF value was recorded for gynecological ailments (0.92), followed by nervous and psychosomatic problems (0.90) and digestive system diseases (0.89). Traditional medicinal knowledge and medicinal plants are under threat due to conservative inheritance processes and anthropogenic pressures for various reasons. Conclusion A rich diversity of medicinal plants is distributed in the Mulam area, and these plants play an important role in healthcare among the Mulam people. Mulam people are skilled in using the plants in their surroundings to treat diseases in their daily lives. However, their traditional medicinal knowledge and medicinal plants are greatly threatened by rapid economic development for various reasons. Thus, policies and practices for the conservation of medicinal plants and the associated traditional knowledge are necessary.


Background
Medicinal plants have been used for many centuries not only in rural areas but also increasingly by urban citizens in both developing and developed countries [1][2][3][4][5][6][7]. According to the World Health Organization (WHO), approximately 80% of populations worldwide depend on herbal medicine for their healthcare needs, especially in rural areas [8]. In developing countries, traditional medicines provide an inexpensive source of primary health care due to the lack of modern health facilities [9,10].
Herbal medicines have been widely accepted in China since ancient times. Shennong Bencao Jing (Shennong's Herbal Classic) was the first book that systematically introduced and described traditional medicinal plant knowledge in the Eastern Han Dynasty (25 AD-220 AD) [11]. Traditional medicinal plants currently play an important role in protecting people's lives and health in ethnic minority regions, especially in remote and lessdeveloped areas [12][13][14][15][16][17].
Guangxi is an autonomous region of ethnic minorities, with Zhuang as the main group, and of multiethnic groups living together. The herbal medicinal markets during the Dragon-Boat Festival are very famous in the Zhuang and Yao communities of Guangxi [18][19][20]. Most members of ethnic minorities live in mountainous or hilly areas, and they are very good at using and naming the medicinal plants in their surroundings [21][22][23][24][25].
The Mulam are an ethnic group native to Guangxi, with a population of more than 210,000 [26]. Nearly 80% of the Mulam people live in Luocheng Mulam Autonomous County, Guangxi [26,27]. Mulam people believe that human beings are an organic combination of "lingqi" (the energy that sustains living organisms), blood, tissue, bone, and muscle. They advocate "the unity of nature and man," that is, harmony among people and between people and nature, with attention paid to both physical and mental health. "The unity of nature and man" is expressed in daily life as, for example, family members of all ages poking fun each other and through collective activity, such as the lion dance, dragon dance, monkey jumping, "zoupo" (antiphonal folk song singing by young people), and so on; these activities are beneficial to mental and physical health [28]. In their long history, Mulam people have accumulated rich folk medicinal knowledge and described many unique experiences in treating common local diseases (e.g., traumatic injuries, cough, diarrhea). Mulam folk medicinal knowledge has been enriched and developed through the process of use; this knowledge plays an important role in local daily life but has not been scientifically reported or studied. In addition, traditional medicinal knowledge is greatly threatened due to the lack of a written record and to conservative inheritance patterns. Young people prefer to look for higher-income jobs in urban areas and are not interested in traditional medicinal knowledge. Therefore, the investigation and documentation of medicinal plants and the associated indigenous wisdom are necessary. This study investigated medicinal plants and related traditional knowledge of the Mulam people, analyzed their ethnic medicinal characteristics and current threats, and proposed conservation strategies.

Study area
The study area is Luocheng Mulam Autonomous County, where the Mulam people live. Luocheng Mulam Autonomous County is situated in the subtropical zone between 24°38′ and 25°12′ east longitude and between 108°29′ and 109°10′ north latitude, with an annual average temperature of 19°C and annual rainfall of 1566 mm. The vegetation category is the subtropical evergreen montane forest [26,28]. Most Mulam villages are located on small strips of flat land or slopes in the karst mountainous area of southern Luocheng Mulam Autonomous County (Fig. 1). Based on the characteristics of traditional Mulam settlements and suggestions from local government officials, 12 villages (Xinan, Maan, Lining, Shuangzhai, Dashan, Youdong, Pingluo, Dafu, Lee, Dashanjiao, Deyin, Sanjia) and five townships (Dongmen, Xiali, Siba, Xiaochangan, Qiaotou) were selected as the investigation sites (Fig. 2).
Mulam settled in Luocheng during the Pre-Qin Dynasty (twenty-first century BC-221 BC) [26,27]. The Mulam language is part of the Dong-Shui branch of the Zhuang-Dong language group in the Chinese-Tibetan language family. The Mulam language has its own independent and complete language system and preserves the language of the ancient Yue people [29]. Mulam people have multiple beliefs. They believe that every village or region is protected by a deity, so they have constructed temples around their villages, such as "Shewang," "Powang," "Tuzhu," "Zaowang," and "God of Mountain" [28]. They also believe in Taoism and Buddhism. They grow rice, corn, and potatoes as staple foods. Cats and snakes are their taboo foods. Most Mulam people engage in traditional agriculture and can identify common herbal medicines and treat common diseases. For example, they use Artemisia argyi for traumatic injuries, Lobelia chinensis for wound healing, Sarcandra glabra for the common cold, and so on [28].

Ethnobotanical data collection
A total of 128 informants (81 males and 47 females) were interviewed in the study area. Among them, 84 informants were selected using the snowball method from the herbal medicinal market and Mulam villages, and 44 key informants were selected purposively and systematically after visiting local officers, village leaders, agricultural technicians, and other people in the study area via a reconnaissance survey prior to data collection. Local healers were automatically qualified as key informants who are custodians of indigenous knowledge of medicinal plants [30]. The informants were local inhabitants aged between 32 and 86 years old. Before each interview, prior informed consent was requested, and throughout the study, international codes of ethics were respected. After obtaining consent, various strata of participants (traditional healers, farmers, village leaders, religious leaders, and health officials) were interviewed.
Ethnobotanical data were collected from January 2013 to April 2017. Information about the medicinal use of plants was collected through semistructured interviews, observations, field visits, and group discussions in the investigation area [22,[31][32][33]. Interviews and discussions were performed based on a checklist of questions prepared in Chinese and translated into the Mulam language. The local names of the plants, the ailments treated by the plants, the plant parts used, the condition of the plant material, the modes of preparation, and the routes of administration were carefully recorded during the interviews with the informants. Vegetation categorization information was also requested and recorded. Other information, including the name, age, occupation, and education level of the informants, was collected in detail. Furthermore, we also recorded the geographic locality and date of the interview. Group discussions were conducted about the conservation of and threats to medicinal plants and traditional knowledge. In addition, the key informants were asked to perform preference ranking exercises.

Specimen collection and identification
Field observations were performed with traditional healers to identify the morphological features and habitats of each medicinal plant species. Voucher specimens and photographs of the local medicinal plants were collected from the field and from home gardens, and the habits and habitats of these plants were recorded. For future reference, voucher specimens were made and deposited in the Herbarium of Guangxi Institute of Botany (IBK), Guangxi Zhuang Autonomous Region and Chinese Academy of Sciences, Guilin, Guangxi, China.
Voucher specimens and photographs were identified and confirmed according to Flora of China, Flora of Guangxi, and botanical websites (e.g., http://www.tropicos.org/, http://www.cvh.ac.cn/search, http://www.plant. csdb.cn/). Finally, the identified specimens were reaffirmed by taxonomic experts from IBK, and the inventory of medicinal plants was completed.

Data analysis
Data analysis was carried out by using ethnobotanical investigation and descriptive statistical methods, such as frequency and percentage, to evaluate the importance of the plant species mentioned in the study area.
Preference ranking exercises [32][33][34] were conducted by asking informants to rank the most important medicinal plants that were frequently used by the local people based on their preference and the importance of the plant in the community. The plants in this exercise were shortlisted by the key informants, and then their importance in managing diseases was discussed. The ranking was based on the efficacy of the medicinal plants. If a medicinal plant was believed to be the most effective for a disease, it was given the highest value of 10 for the selected disease. In contrast, the least-effective plant would be given a value of 1. Each plant species was given a ranking based on its total score. The total ranking for the preference exercise was obtained by summing the number of informants who participated [28]. The informant consensus factor (ICF) was calculated to determine the effectiveness of the medicinal plants in each ailment category according to Heinrich et al. [31]. The formula is provided below: nur is the number of individual reports of a plant use for a particular illness category and nt is the total number of species used by all informants for this illness category.
The fidelity level (FL) was calculated for each of the 15 preferred species for their popularity according to the key informants who cited them in the treatment of particular ailments [31,35,36]. The formula is provided below: I p is the number of informants who suggested the use of a species for the same major purpose (therapeutic use) and I u is the total number of informants who mentioned the plant species for any use.

Demographics of the informants
A total of 128 informants, 84 of whom were general informants and 44 of whom were key informants, from Luocheng County agreed to participate in this study. The distribution of informants by age, gender, and education level is shown in Table 1. The age of the informants ranged from 32 to 86 years old. Among them, 82.3% of informants were over 40 years old, 58.59% of informants had only a primary education, and 12.5% were illiterate. There were more male informants (81, 63.28%) than female informants.

Medicinal plants recorded
From the study sites, a total of 456 medicinal plant species belonging to 350 genera and 132 families were documented. Ethnomedicinal information for each species, including its scientific name, Chinese name, Mulam name, family name, habit, habitat, plant parts used, cited sources, preparation, and use, is listed in Table 2.

Preparation and application methods
There are numerous different ways to prepare medicinal plants to treat human ailments. In the study area, the most common methods of preparation of traditional medicines from plant material were decoction (54.11%), followed by pounding (20.48%), preparing a medicinal liquor (9.64%), raw (9.64%), stewing (2.75%), and others (Table 4). Table 5 shows that the traditional medicines are used in four main ways. The most common method is oral administration (390 plant species, 62.70%), followed by external application (143 species, 22.99%), a medicated bath or rinsing (87 species, 13.99%), and chewing (two species, 0.32%).

Diseases treated in the study area
Based on our investigation and records, medicinal plants were used to treat 312 human ailments in the study area. Based on the statistical analysis, rheumatism was the most common disease treated with 84 medicinal plant species, followed by traumatic injury (71 species), cough (68 species), diarrhea (54 species), jaundice (47 species), abscesses (42 species), furuncles (38 species), edema (36

Ranking and informant consensus factor of medicinal plants
Among all of the ailments in the study area, rheumatism was the most common disease and was treated by a high number of medicinal plants (82 species). Ten medicinal plant species were used effectively to treat rheumatism according to key informants. The results revealed that Semiliquidambar cathayensis was the most preferred medicinal plant for rheumatism, followed by Tetrastigma planicaule, Bauhinia championii, and Millettia lasiopetala (Table 6).
Twelve ailment categories were identified based on the eight systems of the human body and the medication characteristics of the Mulam people. The ICF was calculated for each ailment category, and the range was from 0.51 to 0.92 ( Table 7). The highest ICF (0.92) was reported for gynecological ailments, with 12 species and 138 use reports, followed by nerves and psychosomatic problems (0.90), digestive system diseases (0.89), urinary system diseases (0.88), skin diseases (0.88), and circulatory system diseases (0.88).

Fidelity levels of most commonly used plants by key informants
For each of the 15 most commonly used plant species as ranked by key informants, the fidelity level (FL) ( Table 8) was calculated to quantify their importance in treating a major ailment [31,35]. The results showed a high FL of greater than 50% for 12 plant species, which highlights the importance of these species in the treatment of the frequently mentioned diseases in the study area. Polygonum multiflorum, Semiliquidambar cathayensis, Zingiber officinale, and Striga asiatica had FLs of 100% for strengthening the body and treating rheumatism, infantile malnutrition and cough.

Threats to traditional medicinal knowledge and medicinal plants
According to our investigation (Table 1), more than 80% of key informants who showed mastery of rich traditional medicinal knowledge were over 50 years old, and more than 60% of key informants were illiterate or had only received a primary education. Currently, Mulam children spend most of their time in schools, where they receive mainstream culture and education and have no chance to study traditional medicinal knowledge. In addition, young people prefer to look for jobs in urban areas to earn higher incomes. Furthermore, Mulam healers are unwilling to pass on their traditional medicinal knowledge to young people under 30 years old.   During our surveys, we found that one-third of doctors did not have a successor. The inheritance process of traditional Mulam medicinal knowledge is experiencing a dilemma. In addition, due to the lack of a written language, basic information on the use of plants, the parts used, drug preparation methods, diseases treated, and other information may be lost or discarded in the transmission process. According to our field investigation and the group discussions, most of the medicinal plants were found to be under threat from anthropogenic pressure, such as agricultural activities, firewood collection, overgrazing, and logging. Most Mulam villages are located on small strips of flat land or slopes in karst mountainous areas, and most Mulam people engage in traditional agriculture (Fig. 1). Informants ranked agricultural activities as the most serious threat to medicinal plants, followed by firewood collection and overgrazing. The overharvesting of wild medicinal plants was also a key threat because Mulam people prefer to collect whole plants, roots, stems, and rhizomes. This collection method damages or totally destroys the plant and diminishes the sustainability of medicinal plant use.

Characteristics of informants and their traditional knowledge
Our study included a similar number of men and women as general informants, who have less traditional medicinal knowledge than key informants. Most informants only knew a small number of medicinal plants for treating some common ailments, such as traumatic injuries, abdominal pain, and diarrhea. Every key informant knew more than 60 species and more therapeutic methods for different diseases than the general informants. Most of the key informants were male because Mulam women mainly perform housework and farm work. According to the customary inheritance practice, local traditional medicinal knowledge is typically passed on from an older herbalist to a male successor, rather than a female successor. The number and use methods of medicinal plants reported increased with informant age. Older informants possess more traditional knowledge of medicinal plants than younger people. Local herbalists are unwilling to pass on traditional medicinal knowledge to people who are under 30 years old because they believe that young people are too immature to seriously learn the traditional knowledge. Differences in knowledge of medicinal plants among age and gender groups were also reported in other studies from China and other countries [10,14,37,38].
Most informants in our study have attained low levels of education. Only 33 informants received secondary education, and four informants received tertiary education. Currently, highly educated people tend to prefer modern medicinal technology to traditional knowledge. They are not interested in studying or practicing ethnomedicinal knowledge, especially younger generations. Similar results from other studies also reported that most traditional medicinal herbalists and inheritors worldwide have low formal education levels [10,15,17,22].

Methods of medicinal plant collection and patient diagnosis and treatment
According to our investigation, local herbalists believe that it is much better to collect medicinal plants from noon to evening in autumn or winter because many medicinal plants may enter dormancy and have relatively dry bodies with the highest efficacy. The herbalists also said that if they met a pregnant woman or someone combing their hair on their way to pick medicinal plants, the collected medicinal plants would have a negative impact on the medication made from the plant. Therefore, the herbalist would not go to collect medicinal plants on that day. They reported that if the first herb were obtained very easily, all of the medicinal plants collected on the same day would have good efficacy. In addition, when Mulam healers collect medicinal plants, there is a tradition of "keeping a line," that is, they will put money and rice under the roots of the collected plant and leave a few organs rather than collecting the whole plant.
The Mulam herbalists would let their patients rest for 10-20 min to allow their heart rhythm to normalize before feeling their pulse and inquiring about their condition. Many herbalists would diagnose the disease in combination with the hospital's inspection report. They would ask patients to go to the hospital for a recheck to ensure that the disease would be cured by the end of their therapy. The key informants believed that when  [22,25,37,39]. The herbalists grew a few plants in their home gardens that have multiple uses, are critically endangered in the field, or are urgently needed, such as Paris polyphylla var. chinensis and Cynanchum atratum.
The medicinal plants most widely used by Mulam people were obtained from herbs, which constituted the largest habit category with 246 species (54%). This finding is consistent with other results [37,[39][40][41]. To explain this phenomenon, Moa et al. suggested that herbs are more widely distributed (roadsides, home gardens, farmlands, and wild habitats) than plants with other habits, such as trees, shrubs, and lianas [30]. In addition, herbs are more easily gathered than tree species [41].
Mulam people like to use whole plants (182 species, 33.46%) in the preparation of traditional drugs, and similar results were found in the neighboring Maonan, Yao, and Zhuang communities [24,38,[40][41][42]. The use of roots (73 species, 13.42%), stems (46 species, 8.46%), and rhizomes (30 species, 5.51%) was also common in the study area. However, a clear relationship exists between plant parts collected or the collection method and the impact on the harvested plant [42]. The collection of whole plants, roots, stems, and rhizomes damages or totally destroys the plant and negatively affects the sustainable use of the species. Mulam healers believe that different parts of the same plant may have different medicinal efficacy. The root and stem of Kadsura longipedunculata, for example, are decocted and taken orally for gastritis, and a medicinal liquor made from the fruit is taken orally to treat rheumatism and stomachache. The herbalists also reported that different parts of different plants may have the same medicinal purpose. For instance, the stem of Sargentodoxa cuneata, the root of Semiliquidambar cathayensis, the stem of Tetrastigma planicaule, and the whole plant of Zanthoxylum nitidum could be used to treat rheumatism.
Mulam healers are skilled at using the principle of "lingqi" and have a tradition of "treating diseases using medicine with a similar shape or color." The herbalists reported using medicines from hollow-stem plants such as Equisetum hyemale, Siegesbeckia orientalis, Leonurus japonicus, and Coix lacryma-jobi var. ma-yuen to treat edema based on the aeration of the hollow stems. The branch joints of Achyranthes bidentata, Polygonum capsicum, and Taxillus chinensis are similar to human joints and are often used to treat arthritis. Black soya bean, black sesame seed, mulberry, black ants, and black fungus have black "lingqi" and can be used for treating prematurely white hair.

Methods of medicinal plant preparation and application
In the study area, various methods used by the local Mulam people for the preparation and administration of medicinal plants were investigated and documented. Decoction (316 species involved, 54.11%) is the most common application method for Mulam people. Mulam people and herbalists believe that decoction accelerates the absorption of medicinal ingredients and improves the taste of medicinal plants. Decoction is cited as the most common method of preparation of herbal remedies and is used widely by other ethnic groups [10,22,[43][44][45][46][47]. Pounding also had a high frequency (119) and percentage (20.48%).
Mulam people and herbalists prefer to prepare fresh materials directly through decoction or pounding. They believe that the raw medicinal plants possess better efficacy than cooked plants. In addition, the rich plant diversity around Mulam villages provides a material basis for the use of raw medicinal plants. Additionally, the raw material may maintain its volatile oils and other ingredients [22]. However, the utilization of fresh plant parts may threaten the plants due to frequent collection, including in dry seasons [30]. Certain measures and methods should be taken immediately to guide and encourage local people to grow medicinal herbs and to store commonly consumed medicinal materials.
Oral administration (390 species involved, 62.7%) is the most common method of administration of traditional medicine by Mulam people. Oral use was considered popular because it is a simple administration method. It has also been found to be widely applied in other studies [10,22,[43][44][45][46][47]. Different additives, such as alcohol, honey, salt, and sugar, are widely used by Mulam healers to improve the flavor, taste, and general acceptability of certain orally administered remedies. In addition, Mulam people often stew animal bones, innards, or meat with medicinal plants. Mulam healers believe that animal organs can nourish the corresponding parts of the human body. For example, chicken liver and Buddleja officinalis, Senecio scandens, and Centipeda minima cooked together can be used to treat hepatitis. Pork kidney and Eucommia ulmoides and Allium tuberosum cooked together are used to improve renal function. They also believe that improving patient nutrition can improve the efficacy of medicinal plants for patients.
Medicinal baths were frequently mentioned during our investigations. Mulam people reported that medicinal baths are safe, simple to perform, and did not result in side effects as an external treatment method. A medicinal bath is usually used for sweating, fever reduction, activating blood circulation to dissipate blood stasis, expelling wind to relieve excess gas, and providing itching relief [18]. Medicinal baths can treat diseases and can also prevent diseases. When taking a medicinal bath, the skin is fully exposed to the medicinal bath water so that the bath constituents with medicinal value can be absorbed [48,49]. Hot water can also stimulate blood capillaries and metabolism. Medicinal baths are commonly used by the Yao and Zhuang people who live in humid mountainous areas of southern and southwestern China [18,37,[49][50][51].

Diseases, ranking, and informant consensus factor of medicinal plants
Based on our investigations, 312 human ailments are treated with medicinal plants by Mulam people. According to our statistical analysis, rheumatism had the highest number (84 species) of medicinal plants used for its treatment. Mulam people living in humid and mountainous areas engage in heavy manual labor to survive. Thus, rheumatism is the most common disease in the study area. Because of the complexity of rheumatism, its pathogenesis has not been fully clarified [52]. Rheumatism is common all over the world and has been studied by different research institutions and organizations [52][53][54][55]. Numerous medicinal plants are used by Mulam herbalists to treat rheumatism. Ten medicinal plant species are widely used to treat rheumatism according to the key informants. In the preference ranking exercise, Semiliquidambar cathayensis was the most preferred medicinal plant. S. cathayensis is mainly used to treat rheumatism, lumbar muscle injury, hemiplegia, traumatic injury, and other conditions [56]. It is a very popular and effective traditional local medicine for rheumatism in Yao communities [37]. Mulam healers prefer to use the roots and bark of S. cathayensis collected from the wild to treat rheumatism. The largescale collection of roots and bark threatens the sustainable development of S. cathayensis. Alternative plant parts or species for treating rheumatism urgently need to be discovered and studied.
Most of the ailment categories had a high ICF value (greater than 0.7), such as gynecological ailments (0.92), nerves and psychosomatic problems (0.90), digestive system ailments (0.89), and urinary system ailments (0.88). The higher the ICF value is, the higher the diversity of plant species used by herbalists to treat the disease. The lower the ICF value is, the lower the number of plant species used by herbalists to treat the disease [31]. The high ICF for gynecological ailments can probably be attributed to the local people preferring to obtain medicinal plants from wild habitats nearby, inheriting traditional medicinal knowledge from their parents or grandparents, and having little communication with other people to prevent others from stealing relevant prescriptions. The category of plants used to strengthen the body and release pain had the lowest degree of consensus (0.51) because most of these medicinal plants are easily obtained and used for multiple purposes, such as foods, vegetables, and tea substitutes.

Fidelity levels of the most commonly used plants by key informants
Polygonum multiflorum, Semiliquidambar cathayensis, Zingiber officinale, and Striga asiatica have the highest fidelity level (FL) values (100.00%). Eriobotrya japonica (94.74%) and Sophora tonkinensis (92.00%) also have high FL values. The remedies for frequently reported ailments have the highest FL values, and those with a low number of reports have the lowest FL values [36]. Obviously, these medicinal plants were very effective in the treatment of premature hair graying, rheumatism, infantile malnutrition, cough, and stomachache, which are frequently reported in the Mulam district and widely used by Mulam healers. Additionally, E. japonica (38), Gynostemma pentaphyllum (42)

Comparison with traditional Chinese medicine and previous ethnobotanical studies
To assess the novelty of the ethnomedicinal use of the encountered species, we chose 33 frequently or uniquely used medicinal plant species and compared their use with traditional Chinese medicine (TCM) and previously published reports from neighboring areas of southern China (Table 9) [18-20, 22, 25, 37, 39, 50, 51, 57-66].
The comparison showed that the diseases treated with the most frequently used plants by Mulam people were similar to those found in previous ethnobotanical studies and TCM. For example, Acorus tatarinowii was the most frequently used plant for epilepsy, phlegm heat, abdominal distension, abdominal pain, and traumatic injury in the study area. Similarly, it is used to treat epilepsy and phlegm heat in TCM [57]. In addition, this plant is used for rheumatism and beautification in the Yao communities of Longsheng County, Northern Guangxi [25], and it is used to treat stomachache, stomach flu, limb numbness, hemorrhoids, diarrhea, gall, injuries from falls, and dysmenorrhea and as an invigorant by Yao people in Jinping County, southeastern Yunnan [50]. In Guangdong, this plant is used to treat flu, detumescence, and pain by Hakka people [59]. There are some similarities and differences in the diseases treated with A. tatarinowii, and it is used in different places and by different groups of people. However, some unique medicinal plant species (e.g., Achyranthes longifolia, Cupressus funebris, Euphorbia esula, Flemingia macrophylla, Laportea violacea, Pinus massoniana, Toxicodendron vernicifluum, Viburnum taitoense) had completely novel medicinal functions reported in our study area that had never been reported in other investigations or recorded in TCM. For example, A. longifolia was reported in the present study as only being used for calculosis, whereas it is used for traumatic injury, rheumatism, dysentery, diphtheria, sore throat, sore carbuncle, stranguria, and edema in TCM [57]. In southern and southwestern China, this plant was used to treat blood stasis, empty-kidney lumbago, sore throat, dysmenorrhea, hypertension, and traumatic injury by Yao and Miao people [20,58]. Euphorbia esula is another species mentioned for the first time. It was reportedly used as a disinfectant and to treat chills and fever in a medicinal bath or by placing it on the patient's bed. Previous studies conducted in other areas mentioned the use of Euphorbia spp. to treat rheumatism, promote blood circulation, cure furuncles, and treat inflammations of unknown origin [22,61]. V. taitoense is a Viburnum medicinal species mentioned for the first time. It was reported as being used to treat hyperosteogeny, protrusion of the lumbar intervertebral disc, pain, and traumatic injury in the current study. Previous studies conducted in other areas mentioned treatment with Viburnum spp. for toxicoderma, rheumatism, traumatic injury, and to stop bleeding [25,61]. The pharmacological activity of these plants is a novel finding that has only been reported for such medicinal purposes in this area. Our investigation found that traumatic injury, bacterial infection, calculosis, hyperosteogeny, cough, and fever were the most common diseases in Mulam villages. Mulam people are skilled in using plants from their surroundings to treat diseases in their daily lives. They not only make full use of the surrounding plant resources but also continuously communicate and learn from other ethnic groups in their long-term struggle with the natural environment and diseases.

Threats to traditional medicinal knowledge and medicinal plants
Our investigation and group discussions revealed that traditional medicinal knowledge is greatly threatened due to the lack of a written record, conservative inheritance patterns, and low interest in traditional medicinal knowledge from young people. In addition, agricultural activities, firewood collection, overgrazing, logging, and overharvesting of medicinal plants resulted in a decrease in medicinal plant resources and associated traditional knowledge. Additionally, the superstition and the mystery surrounding the Mulam healers' traditional medicinal knowledge are also regarded as obstacles to dissemination and promotion. Thus, policies to improve the conservation, development, and sustainable use of Mulam medicinal plants and associated traditional knowledge are essential. First, further investigation and documentation of traditional Mulam medicinal knowledge is imperative. Books and databases of medicinal plants, animals, and minerals should be published, with free access provided to local healers and those (especially young people) who are interested in Mulam ethnomedicine. Second, advanced theories and methods of pharmacology, chemistry, and molecular biology should be applied to study the traditional Mulam medicinal knowledge and enhance Mulam people's understanding and confidence. Third, it is also necessary to encourage the Mulam people to conserve medicinal plants in situ and ex situ, such as by planting endangered and preferred medicinal species in their home gardens or farmlands.

Conclusions
A total of 456 medicinal plant species used by Mulam people to treat 312 human ailments were investigated and recorded. This result reflects the rich diversity of medicinal plants in the Mulam area. These medicinal plants play an important role in the Mulam healthcare system. Most of the plants (335 species, 73.47%) were obtained from wild habitats, and the herbaceous habit was the most common growth habit (246 species, 54%). The most common method of administration was oral administration, which was used for 390 species (62.70%), and the most common method of