Abstract
Introduction
Hypericum perforatum L. is one of the most important species of the genus Hypericum. This plant is a perennial herbaceous plant with great adaptation ability. Therefore, St John's Wort can be found widespread throughout the country from sea side levels to 2000m altitude. It is also one of the most important medicinal plants in the world due to its various positive and well-known medicinal properties, especially in the treatment of depression. Hypericin and Hyperforin are known as the main bioactive compounds of this medicinal plant. Due to the high dispersion of Hypericum plants in Iran, this experiment was conducted to evaluate 15 populations of Hypericum plants at flowering stage using morphological and biochemical properties in order to indicate the best metabolite producing population.
 
Materials and Methods
Plant materials were selected randomly at full flowering stage from 15 different populations at full bloom in different provinces during summer 2017. Morphological features such as height of plant, number of flower stalk, length of flower stalk, number of non-flower bearing stems, number of flowers, height of the lowest and the highest leaf were evaluated. Plant materials were then dried at room temperature and kept in dark for analysis. Leaf and petals were ground and extraction was conducted by methanol. Hypericin and Hyperforin content of leaves and flowers were evaluated by HPLC equipped with DAD detector. Antioxidant activity of leaves and flowers of Hypericum samples were evaluated by DPPH scavenging assay. Phenol content was evaluated by Folin–Ciocalteu (F‐C) reaction. Total flavonoid content determination was also conducted by a spectrophotometric assay based on aluminium complex formation.
 
Results and Discussion
The results showed that there was a significant difference between different populations in terms of morphological traits. The highest aerial part height was seen in ‘Khoramabad’ population with a value of 92.44 cm. ‘Nahavand’ population had the shortest height with a value of 49.55 cm. The largest number of flower stalk was seen in ‘Sarpol Zahab’ population with 16.48 flower stalks. This was while ‘Firoozkouh’ population had the least number of flower stalks. ‘Sijan’ population had the most non-flower bearing stems, while ‘Shazand’ had the least number of non-flower bearing stems. There was a significant difference between antioxidant activity in leaf and flowers of the studied populations. The highest antioxidant activity was observed in ‘Borojerd’ population. Total Phenol content and flavonoids also differed not only among populations, but also between leaf and flower. ‘Sarpol Zahab’ had the highest total Phenol content in between the studied populations. This was while ‘Nahavand’ population had the highest flavonoid content. The results also revealed that the flowers had the highest levels of Hypericin and Hyperforin compared to leaves. The levels of Hyperforin in both organs were significantly higher than Hypericin in all studied populations.
 
Conclusion
In general, it can be concluded that there is a high variation among different populations and this variation can be used to identify populations with high yields and high levels of effective substances in breeding programs.