Climatic and Topographic Drivers of Flavonoid and Scutellarin Accumulation in Yunnan’s High-quality Erigeron breviscapus

Erigeron breviscapus (EB), a renowned Chinese medicinal plant in Yunnan's Luxi and Shizong Counties, is rich in total flavonoids and scutellarin, but systematic studies in Luxi are limited. This study analyzed 260 cultivated EB samples, examining spatiotemporal variations of these components and their relations with climate and terrain factors. Yongning Town was identified as the core production area because concentrations of scutellarin and total flavonoids in EB were highest in this region, and optimal levels of flavonoids and scutellarin were observed in August. Although the growth duration did not affect the total flavonoid content, it significantly reduced scutellarin levels, and the optimal harvest window was 30–50 days. Scutellarin concentrations increased with average temperatures, whereas total flavonoids remained stable at 6.17 ± 0.64%; however, day–night temperature differences over 10 °C inhibited scutellarin accumulation. The concentrations of compounds were highest at altitudes of 1,400–1,600 m when the UV radiation was less than 100 J/cm ² . Redundancy analysis revealed that growth duration was positively correlated with total flavonoids but negatively correlated with scutellarin, and the opposite pattern was observed for average temperature; both compounds were negatively associated with UV, temperature variation, and altitude. Principal component analysis revealed that UV flux and temperature differences were the key environmental factors; cluster analysis revealed that low-altitude regions (<1,600 m) and shorter growth cycles (30–50 days) promoted scutellarin accumulation, while extreme cold, long growth durations (>70 days), and large day–night temperature differences (>10 °C) suppressed scutellarin biosynthesis. Overall, UV radiation and day–night temperature difference were the critical factors affecting scutellarin accumulation, and optimal EB growth was observed under the following conditions: altitudes of 1,400–1,600 m, temperatures of 7–9 °C, UV radiation below 100 J/cm², and a harvest cycle of 30–50 days.