Natural Diversity of <i>Crataegus monogyna</i> Jacq. in Northeastern Türkiye Encompassing Morphological, Biochemical, and Molecular Features

Hawthorn (<i>Cratageus monogyna</i> Jacq.), one of the important wild fruit species in Turkey, is an important fruit species in many countries due to its use in traditional medicine, landscaping studies, and the food and beverage industry. In this study, morphological characterization revealed significant variation among genotypes, with fruit weight ranging from 0.55 g to 2.87 g, fruit width from 9.74 mm to 18.39 mm, and leaf width from 19.53 mm to 41.19 mm. Genotype-dependent variations were observed in the total phenolic content (151.34 mg–491.88 mg GAE 100 g⁻¹ flesh), the total flavonoid content (16.74–48.13 mg CAE 100 g⁻¹ flesh), the total anthocyanin content (26.34–79.79 mg cyn-3 gluc 100 g⁻¹ flesh), and the antioxidant activity (29.20% to 56.70%). HPLC-based phenolic profiling identified substantial variations in key bioactive compounds, with the highest levels of chlorogenic acid (16.16 mg 100 g⁻¹ fw), caffeic acid (10.21 mg 100 g⁻¹ fw), epicatechin (13.83 mg 100 g⁻¹ fw), rutin (74.05 mg 100 g⁻¹ fw), and protocatechuic acid (2.00 mg 100 g⁻¹ fw). ISSR marker-based molecular analysis revealed a high degree of genetic polymorphism (89.12%), with 55 out of 62 bands classified as polymorphic. The polymorphic information content values ranged from 0.34 to 0.44. The Jaccard similarity coefficient ranged from 0.04 (M9 and M16) to 0.63 (M17 and M3), indicating substantial genetic variability. The tanglegram analysis comparing genetic and morphological–biochemical dendrograms yielded an entanglement score of 0.714, indicating an alignment between molecular and phenotypic data. These findings show that hawthorn genotypes from the Kelkit Valley exhibit extensive genetic and biochemical diversity, which is critical for conservation efforts, breeding programs, and the development of high-value medicinal and functional food products.