Sampling
In 2011–­2015, we sampled 27 populations throughout the distribution range of the seven Scutellaria species in Taiwan. Four of these populations exhibited sympatry: two where both S. indica andS. barbata were present, one where both S. austrotaiwanensis and S. taiwanensis were present, and one where both S. playfairii and S. tashiroi were present (Fig. 1; Table S1). Species identification of the collected samples was based on Hsieh (2013), Hsieh and Huang (1995), Hsieh and Huang (1997), and Chao et al. (2020). Fresh leaves from 4–46 individuals per population were collected and dried in silica gel. The latitude, longitude, and altitude of each sampling site were recorded (Table S1). A total of 504 individuals from 27 populations were sequenced in this study, making this the most comprehensive sampling of Scutellaria on Taiwan Island.