Traditional culture and preparation process of Laji-He

The origin of Laji-He is closely linked to the rich folklore and traditional culture of the Beibu Gulf region in Guangxi. Every year, on the eighth day of the fourth lunar month, a traditional festival is celebrated, and consuming Laji-He on this day has become a custom passed down through generations. The name Laji-He is thought to come from the belief that this dish, made from a blend of medicinal herbs and rice, helps cleanse the body of harmful substances, often referred to as "garbage," symbolizing illness—hence the name "garbage rice cakes."

According to local folklore, the eighth day of the fourth lunar month is also considered the day when deities bring medicinal herbs to the human world. According to the locals, on this day, the toxicity of herbs is believed to be extremely low, and even normally toxic plants can be consumed without causing harm. This day is thus referred to as the "Herb Festival." As a result, locals enjoy consuming various herbs on this day to promote health and ward off illness. This belief encourages people to experiment with a wide range of herbs, and many households add over 20 different herbs to Laji-He on this day, believing that the more herbs included, the stronger their medicinal effects. In addition to eating Laji-He, locals also boil herbs to bathe their children, believing this ritual wards off evil and prevents illness. Thus, Laji-He is more than just a traditional food; it is a cultural symbol of health and blessings.

Our interviews revealed that Laji-He is also consumed on the third day of the third lunar month and the fifth day of the fifth lunar month (Dragon Boat Festival), which are also important traditional festivals locally, but the scale and frequency of consuming the Laji-He are much smaller compared to the eighth day of the fourth lunar month. In Beihai, for instance, Laji-He is mainly made with Paederia foetida and a few other plants, with limited use of additional species.

We also conducted a detailed investigation of the Laji-He preparation process (Fig. 3). The first step involves soaking the rice (or glutinous rice) either the day before or on the day of preparation, followed by draining and cleaning the soaked rice. The rice is then mixed with finely chopped herbal leaves and ground into a fine powder using a machine. To ensure a better texture, the ground rice flour is sifted, resulting in a finer and smoother consistency. Next, the mixture is then shaped into various forms, such as strips, rectangular blocks, or round cakes, depending on individual preference, and placed in an oiled steamer tray. The steamer water is brought to a boil, and the Laji-He is steamed for approximately 15 min. Once fully steamed, the Laji-He emits a pleasant fragrance of plants and rice. It can be eaten directly or cut into strips and boiled with sugar syrup to make sweet soup of Laji-He, offering a richer flavor.

Fig. 3

Preparation process of Laji-He. A Herbal medicine selling stand, B Pairing medicinal herbs, C Medicinal herb combinations, D Medicinal herbs mixed with glutinous rice, E Herb and glutinous rice mixture ground into powder, F Herb and glutinous rice mixed powder, G Molding Laji-He, H Steamed Laji-He, I Laji-He sweet soup

Analysis of the diversity of medicinal plants in Laji-He

We recorded a total of 63 medicinal plants belonging to 53 genera within 36 families used in the preparation of Laji-He in the Beibu Gulf region (Table 2). The majority of the species are used in detoxification in TCM.

Table 2 Inventory of plant materials used in Laji-He

In terms of family distribution, Rubiaceae is the most represented, with six species, followed by Fabaceae with five species, and Lamiaceae with four species. As shown in Table 3, families with five or more species account for only 5.56% of the total number of families, but represent 17.46% of the total species. Families with 2–4 species make up 36.11% of the total families and nearly half (49.21%) of the total species, indicating the significant role of these moderately sized families in the formulation. Single-species families, which make up 58.33% of the total families, contribute 33.33% of the total species.

Table 3 Analysis of families and genera of medicinal plants in Laji-He

The distribution of genera is relatively dispersed, with Paederia and Persicaria being the most represented, each containing three species. This pattern suggests that the overall distribution of genera is balanced, with no single genus dominating the formulation of making Laji-He. The genera with 2–4 species account for 12.96% of the total genera, contributing 25.40% of the species, while single-species genera make up 87.04% of the total genera, representing 74.60% of the species (Table 3). This distribution indicates that most genera in Laji-He contain only one species, reflecting a broad utilization of plant species.

Analysis of life forms and resource types

The life forms of the plants used in Laji-He show a clear distribution pattern, with herbaceous plants making up 49.21% of the total, indicating their important role in the formulation. Shrubs account for 22.22% and trees for 19.05%, reflecting the common use of both in the plant composition. Vines represent 9.52%, and while fewer in number, they add to the diversity of life forms. This distribution highlights the diverse utilization of plants in Laji-He, with various life forms being widely applied, demonstrating the close connection between this traditional food and local natural resources.

The use of plant resources in Laji-He primarily relies on wild plants. According to the data, 51 wild species account for 80.95% of the total, indicating a strong dependence on natural plant resources by the local people. Cultivated plants and those that can be both cultivated and found in the wild each account for 9.52%, showing that cultivated plants are not the primary source in the formulation of Laji-He, but rather serve as a supplement to wild resources. This reliance on wild resources reflects the richness of the local natural ecosystem. As a traditional food, most of the plants used in Laji-He are not artificially cultivated but are directly gathered from the wild. Due to their infrequent use, this practice does not place significant pressure on the resources. This approach may be closely linked to the local people's long-standing traditions of foraging and ecological knowledge, ensuring the sustainable use of natural resources for the production of Laji-He.

The small proportion of cultivated plants, as well as those that can grow both in the wild and through cultivation, indicates that these species are commonly used in daily life, where cultivation is more convenient and resource-efficient than wild collections. For example, Piper sarmentosum is highly valued for its distinctive aroma and is widely used as both a medicinal and edible plant in local communities. In addition to its role in Laji-He, it is also consumed as a wild vegetable or seasoning.

Notably, none of the plants used in Laji-He are protected or endangered species, which suggests that the production of this traditional food does not burden rare plant resources, allowing for the preservation of cultural traditions while demonstrating a high degree of environmental sustainability. This feature provides a solid foundation for the continued production and cultural transmission of Laji-He.

Medicinal properties of plants used in Laji-He

The analysis of the medicinal properties of the raw plant materials used in Laji-He reveals that the predominant therapeutic categories include heat-clearing and detoxification, expelling wind-dampness, treating traumatic injuries, and hemostasis (Table 4). These therapeutic properties are closely associated with the hot and humid climatic conditions of the Beibu Gulf region, reflecting the local inhabitants' traditional strategies for using plants to regulate bodily conditions, as well as prevent and treat common ailments.

Table 4 Medicinal properties of the plant ingredients used in Laji-He

Among the medicinal properties identified, heat-clearing and detoxifying plants are the most prevalent, accounting for approximately 70% of the total medicinal uses. The Beibu Gulf region is characterized by a hot and humid climate, making the human body prone to damp-heat invasion, which can lead to the accumulation of internal heat toxins, resulting in symptoms such as fever and skin disorders. The use of heat-clearing and detoxifying plants effectively helps the locals eliminate internal heat and maintain health. These plants play an essential role in the daily diets of local communities, helping to regulate the internal environment and alleviate discomfort caused by the damp-heat climate. In the Lingnan region, traditional herbal teas and soups are common components of daily health practices, with heat-clearing and detoxification serving as their primary therapeutic functions [5, 11].

According to the inventory we recorded, the use of plants with wind-dampness-dispelling properties (treating Rheumatic diseases) is similarly widespread, representing nearly half of the total medicinal uses. The prolonged exposure to humid conditions in this region has contributed to the high prevalence of rheumatism and related conditions, particularly among coastal residents engaged in activities such as fishing and shrimp harvesting, which increase the risk of joint pain and muscle stiffness. Plants with wind-dampness-dispelling properties are thus crucial for their ability to dispel cold and dampness, alleviating joint issues caused by the accumulation of moisture in the body. Their therapeutic role extends beyond rheumatism management to the broader prevention of climate-induced chronic ailments.

Plants used to treat traumatic injuries are also widely represented, comprising approximately 40% of the total medicinal uses. This trend is strongly linked to the local labor-intensive lifestyle. Residents of the Beibu Gulf, especially those in rural areas, are frequently engaged in physically demanding activities, which increase the incidence of sprains and other minor injuries. Plants with properties such as promoting blood circulation, reducing swelling, and alleviating pain are, therefore, essential components of external injury management. These plants not only provide effective pain relief but also facilitate the rapid recovery of damaged tissues, making them indispensable in local healthcare practices.

Hemostatic plants also account for a considerable proportion, representing approximately 37% of the total medicinal uses. Although this therapeutic function appears to be unrelated to the direct preparation of Laji-He, it carries significant supplementary value in the daily lives of residents in the Beibu Gulf region. The hot and humid environment often leads to skin injuries and hemorrhagic wounds, especially for individuals engaged in outdoor labor or rural activities. Plants with hemostatic properties are frequently employed to treat minor wounds, facilitating rapid blood coagulation and reducing the risk of infection.

However, it is noteworthy that some of these medicinal plants contain potentially toxic compounds. While traditionally used for routine health maintenance and treatment, modern studies have indicated that certain plants may pose health risks when consumed in excess or over extended periods. Some of these plant constituents have been found to exhibit hepatotoxic or nephrotoxic effects, which necessitates caution in their use. Therefore, in addition to evaluating their therapeutic efficacy, it is critical to assess their safety profile. Although these plants have long been incorporated into local dietary and medicinal practices, further toxicological research is warranted in a contemporary context to ensure their safe application in modern society. The analysis of these medicinal properties demonstrates how residents in the Beibu Gulf region have skillfully utilized local natural resources to address health challenges associated with the damp-heat climate. These plants not only aid in regulating internal moisture and heat, but also play an irreplaceable role in managing traumatic injuries, stopping bleeding, and alleviating rheumatic conditions. Their use reflects the deep interaction between humans and their natural environment and embodies the concept of "food and medicine homology" in traditional wisdom.

Key medicinal plants with high RFC values in Laji-He preparation

The relative frequency of citation (RFC) is an effective measure to evaluate the popularity and frequency of use of specific plants within local communities [7]. A higher RFC value indicates a closer association of the plant with the daily lives of local residents and a higher utilization frequency [7]. In the preparation of Laji-He, certain plants are widely favored due to their medicinal properties, cultural significance, and ease of access. The top five most commonly used plants in Laji-He preparation (Fig. 4), along with their respective RFC values, are as follows: Paederia scandens (RFC = 0.8817), Piper sarmentosum (RFC = 0.7742), Houttuynia cordata (RFC = 0.7312), Centella asiatica (RFC = 0.7204), and Morus alba (RFC = 0.7097). These high RFC values suggest that these plants hold a prominent role in the daily lives of the local residents and are indispensable in the preparation of Laji-He.

Fig. 4

Key medicinal plants with high RFC values in Laji-He preparation. A Paederia scandens, B Piper sarmentosum, C Houttuynia cordata, D Centella asiatica, E Morus alba

Paederia foetida is one of the most widely used plants in the preparation of Laji-He, with the highest RFC value (0.8817) among all documented plant species, indicating its high utilization frequency and widespread application within the local community. As a wild climbing vine of the Rubiaceae family, P. foetida is primarily utilized for its leaves, which are traditionally employed to treat various ailments, including rheumatism, indigestion, heat clearance, detoxification, and abdominal pain relief. The plant is extensively used during the traditional Lunar April 8th festival for the preparation of Laji-He and is also commonly found in the production of medicinal glutinous rice cakes in daily life. This dual role, combining cultural significance and medicinal value, highlights the importance of P. foetida in the daily lives of local residents. Not only does it serve as a symbolic component in festival cuisine, but its consistent medicinal efficacy also makes it a popular ingredient for daily food therapy and healthcare.

In recent years, research on P. foetida has expanded significantly, and its phytochemical composition and pharmacological properties have been systematically documented and received increasing attention [12, 13]. According to the latest reviews, P. foetida is rich in a variety of bioactive phytochemicals, including iridoid glycosides, flavonoid glycosides, anthraquinones, and various terpenoids [12, 13]. These compounds have been shown to possess a range of pharmacological activities, such as anti-inflammatory, antioxidant, antidiabetic, and anticancer effects, in both in vitro and in vivo studies [12, 13]. Among these components, iridoid glycosides are considered the primary bioactive constituents, with paederoside and paederosidic acid being the most notable [12, 13]. These compounds have demonstrated significant analgesic, anti-inflammatory, and antimicrobial effects in various disease models, making them of particular interest for further pharmacological research [12, 13].

Although other species of the same genus, such as Paederia lanuginosa and Paederia pertomentosa, contain similar chemical constituents and exhibit comparable medicinal properties, their RFC values are relatively low due to limited availability and scattered distribution in the region. In contrast, P. foetida, owing to its widespread distribution and easy accessibility in natural habitats, has become the preferred plant material for the preparation of Laji-He and other traditional foods, as well as an essential ingredient in daily dietary therapy within the local community.

In comparison with Paederia foetida, Piper sarmentosum also plays a crucial role in the preparation of Laji-He. As a herbaceous plant belonging to the Piperaceae family, P. sarmentosum, can be cultivated or grown wild, and its leaves are primarily used for medicinal purposes. It is widely distributed in Southeast Asia and the southeastern coastal regions of China, including Fujian, Guangdong, and Guizhou [14]. With a long-standing history in traditional medicine, P. sarmentosum has been utilized for the treatment of wind-cold cough, fever, rheumatism, arthralgia, diarrhea, dysentery, postpartum foot swelling, stomachache, toothache, diabetes, and traumatic injuries [14]. Therefore, in the preparation of Laji-He, P. sarmentosum not only enhances the dish's unique aroma but also contributes to its medicinal efficacy by clearing heat, detoxifying, and dispelling dampness, thus helping to prevent heat-dampness-related disorders. In recent years, the chemical composition and pharmacological activities of P. sarmentosum have been extensively studied. The literature indicates that P. sarmentosum is rich in essential oils, alkaloids, flavonoids, lignans, and steroids, which have been demonstrated to exhibit various pharmacological properties, such as anti-inflammatory, antitumor, antipyretic, anti-osteoporosis, antibacterial, antidepressant, anti-atherosclerotic, and hypoglycemic activities [14].

The use of P. sarmentosum in Laji-He not only reflects its unique flavor and medicinal properties but also extends to its presence in other traditional local dishes, such as stir-fried P. sarmentosum with field snails, P. sarmentosum cakes, and stir-fried dog meat with P. sarmentosum. Additionally, local residents often crush the leaves for external application to treat traumatic injuries, showing significant therapeutic effects. The versatile applications of P. sarmentosum demonstrate its multi-purpose utility and cultural value within the local community, while its medicinal properties lay a solid foundation for further research into its bioactive components and potential drug development.

In addition to Paederia foetida and Piper sarmentosum, three other plants play equally significant roles in the preparation of Laji-He: Houttuynia cordata, Centella asiatica, and Morus alba. These plants are not only considered integral components of traditional medicinal food due to their respective pharmacological properties but have also gradually gained recognition through modern pharmacological research.

Houttuynia cordata, commonly known as fish mint, is a wild herbaceous plant belonging to the Saururaceae family. Its leaves possess multiple therapeutic properties, such as clearing heat and detoxification, promoting diuresis, relieving dysentery, and treating abscesses and ulcers. It has long been used in traditional medicine to alleviate heat-induced dysentery, rhinitis, and constipation [15]. In the preparation of Laji-He, the incorporation of H. cordata not only enhances the flavor of the dish but also contributes to the balance of internal damp-heat conditions, a particularly vital function in the local hot and humid climate [15]. Recent studies have shown that chemical constituents in H. cordata, such as essential oils, flavonoids, and chlorogenic acid, exhibit anti-inflammatory, antiviral, and immunomodulatory activities, thereby providing scientific evidence supporting its traditional usage [16].

Centella asiatica, a wild herbaceous plant of the Apiaceae family, is traditionally used for its medicinal properties, such as clearing heat and detoxification, alleviating toothache and dysmenorrhea, and promoting scar healing [17]. It holds an important position in Laji-He, mainly due to its strong heat-clearing effect, which is particularly beneficial during the hot season. Furthermore, its triterpenoid components have been extensively studied in recent years, demonstrating significant antioxidant, anti-inflammatory, and wound-healing properties, which extend its potential applications beyond traditional medicinal food use [18, 19].

Morus alba, a cultivated tree species in the Moraceae family, is predominantly used for its leaves in the preparation of Laji-He, due to its properties of clearing heat and detoxification, dispelling wind-dampness, and relieving cough and phlegm [20]. The leaves are rich in various alkaloids and flavonoids, which have been reported to possess antidiabetic, lipid-lowering, and anti-obesity effects, making them valuable in the development of modern functional foods and pharmaceuticals [20, 21]. Although the fruits of M. alba are also widely consumed in the daily diet of local residents, the leaves are more extensively utilized in Laji-He preparation, playing a crucial role in balancing internal damp-heat conditions, especially during the hot summer months.

The analysis of the RFC values for these plants indicates that Paederia foetida, Piper sarmentosum, Houttuynia cordata, Centella asiatica, and Morus alba all occupy significant roles in the preparation of Laji-He. In particular, Paederia foetida, with its high RFC value, not only features prominently during traditional festivals but also finds application in daily life. The usage frequency and popularity of these plants not only reflect the local community's strong reliance on their medicinal value but also demonstrate their deep connection with the local natural environment and climate. The incorporation of these plants in Laji-He is more than just a culinary tradition; it serves as an essential tool for local residents to cope with the hot and humid climate and to maintain overall health.