Traditional medicinal bath plants along the Beibu Gulf coast of Guangxi, China

Medicinal baths are a widely practiced traditional health maintenance method in southern China, yet systematic ethnobotanical studies from coastal regions remain limited. The Beibu Gulf coastal area of Guangxi is a biologically and culturally diverse region where such practices are actively maintained. This study aims to document the plant species used in traditional medicinal baths and to characterize their composition, usage patterns, and regional variation.

Ethnobotanical interviews were conducted at 20 sites across Beihai, Qinzhou, and Fangchenggang City, which comprise the Beibu Gulf. A total of 135 informants (62 males and 73 females) were interviewed in medicinal markets and traditional villages. Data on plant species, plant parts used, and medicinal applications were recorded. Quantitative analyses, including Jaccard Index (JI), cumulative contribution analysis, and Gini coefficient, were applied to assess species similarity and usage patterns.

A total of 286 plant species used for medicinal baths were recorded. These plants belong to 92 families and 218 genera. Fabaceae, Lamiaceae, Rubiaceae, and Asteraceae were the dominant families, with monotypic genera prevalent. Herbs were the most common life form (99 species, 34.62%). Branches, leaves, and whole plants accounted for 71.66% of use. The main applications of these plants in medicinal bath practices were for traumatic injuries, rheumatic diseases, and skin conditions (58.50%). Species richness was highest in Fangchenggang (249 species), followed by Qinzhou (238) and Beihai (144), with 133 shared species. Higher similarity was observed between Fangchenggang and Qinzhou (JI = 0.72). The top 10, 20, 30, 50, and 100 species contributed 10.24%, 18.16%, 25.10%, 37.47%, and 62.25% of total usage frequency, respectively, with a Gini coefficient of 0.383.

The medicinal bath plant system in the Beibu Gulf coastal region is characterized by high species richness and a balanced structure of commonly used and supplementary species. While a shared core flora exists, local differences among cities in the Beibu Gulf are also evident. This study provides comprehensive ethnobotanical data from southern coastal China and offers a regional case for understanding plant selection and functional convergence in medicinal bath practices.