Hylomecon japonica (Thunb.) Prantl et Kundig, a medicinal plant of the Papaveraceae family, is widely distributed in Shaanxi, Liaoning, Chongqing, Shanxi, Sichuan, Heilongjiang, and Henan in China, along with Japan and Korea[1]. It is a kind of perennial herb with irregular serrated leaves, and characterized by bright yellow flowers[2]. Meanwhile, its roots have medicinal potential, so it is commonly used in folk to treat diseases such as arthritis, neuralgia, and eczema[3]. Various alkaloids, phenols, flavonoids, saponins and other active compounds isolated from H. japonica have been reported. And a new species of endophytic bacteria belonging to sphingomonas was isolated from the rhizome of H. japonica[4–6]. Although many pharmacological studies, including anti-inflammatory, anticancer and antibacterial activities, have been reported[7–9], the investigation of the medicinal value and mechanism of H. japonica is far from enough. Due to the important medicinal value of the species, the wild resources of H. japonica have been greatly destroyed, and in combination with the climate change, the natural habitat of these plants have been gradually reduced. And most of the previous studies focused on the chemical composition of H. japonica, while other studies focused on the mechanism of its pharmacological action. However, up to now, little information is available on the guidance to protect, develop and utilize the H. japonica resources.
The studies for regionalization of Traditional Chinese medicine (TCM), have been performed to analyze the relationship between the distribution of TCM resources and their surrounding environmental variables. Relevant factors such as ecological environment, geographical distribution, regional characteristics and quality of the TCM were classified. The research on regionalization of TCM began in 1990s. And with the rapid development of science and technology, the research methods of TCM regionalization are gradually improved[10]. The Species Distribution Model (SDM) is the main model used to predict suitable habitats for species in the regionalization of TCM. At present, there are a large number of SDMs and related software that can draw suitable habitat distribution maps of species based on the observed distribution data. The potential distribution of Nelumbo nucifera Gaertn. was assessed in China by the GARP and Maxent[11]; Based on CLIMEX ecological software, the data were compiled and processed to predict the adaptive area of V. taliense Loes. F.[12]; And the BIOCLIM niche model have been used to predict the potential adaptability of Yulania Liliflora (Desr.) D. L, Fu[13]. Among these models, the Maxent model has shown many advantages over other models when applied to "existence-only" species occurrence data, and is widely used for species distribution prediction and habitat suitability assessment.
Combined with some other software such as ArcGIS, Maxent can extract factor variables according to the geographic information of sample collection points to analyze the habitat suitability of species. Furthermore, potentially suitable habitats can be divided into a specified number of levels as needed. Many reports have showed that the Maxent model has been used to analyze the habitat suitability of medicinal plants and ecologically important species in the study of regionalization of TCM. Based on Maxent model and GIS technology, the production regionalization of Angelica in China was studied[14]. By constructing Maxent model, Wang Dan predicted that the high adaptability areas of Bupleurum marginatum were mainly distributed in the border of provinces in the southern region[15]. The spatial analysis function of ArcGIS and Maxent model were used to predict the ecological and quality suitable areas of Gentianae Macrophyllae Radix in China[16]. And the Maxent and ArcGIS were also used to predict the production regionalization and its suitability level of Paris polyphylla Smith var. chinensis (Franch.) Hara. in China[17]. The Maxent model only needs a set of known data (such as longitude and latitude information of sampling points) and variable factors, such as topography, precipitation, soil, temperature, vegetation type. These continuous or classified data are used to predict the habitat suitability distribution by combining the interactions between variables. The model has the characteristics of good performance with incomplete datasets, high efficiency, easy operation, high accuracy, small sample size requirements and high guiding significance[18].
To seek suitable habitats and evaluate the great practical significance for the development of H. japonica production, rational development and utilization and protection of H. japonica resources. In the present study, the occurrence records of H. japonica were collected for habitat suitability assessment. We used Maxent to simulate the suitability of H. japonica habitats on the occurrence records, based on variable factors (including soil, topography, precipitation, bioclimatic variables, temperature, and vegetation type), and analyzed the potential suitable habitats of H. japonica by means of ArcGIS. Maxent model evaluates the accuracy of model calculation results according to receiver-operating characteristic (ROC) curve (AUC), and the key environmental variables related to the geographical distribution of H. japonica were mapped by Jackknife test.