2.1 Sample sites and materials
The sample sites are located at the Hualongshan Mountains National Nature Reserve in Shaanxi Province, with the geographic coordinates 109°16′41″ - 109°30′29″ E, 31°54′39″ - 32°08′13″ N. The highest peak of the Hualongshan Mountains is 2917 m above sea level, which is the second highest peak of the Dabashan Mountains in China. Based on the vegetation regionalization of China, the Hualongshan Mountains belong to the subtropical evergreen broadleaved forest, north subtropical evergreen forest, and deciduous broadleaved mixed forest areas.
In the Hualongshan Mountains, the diploid grows within the long and narrow areas on the shady slopes of gullies, from west to east, whereas the tetraploid grows under the arbor forests at 40° areas of the northern slopes. Ten 1 m × 1 m plots were set in the diploid and tetraploid sample areas, respectively. Within ten samples, a total of 93 and 107 diploid and tetraploid individuals were collected from all the visible individuals in the sample areas. And, the specific spatial positions of each sampled individual of the two ploidies were marked and recorded.