Reticulate evolution in North American black-fruited hawthorns (Crataegus section Douglasia; Rosaceae): evidence from nuclear ITS2 and plastid sequences

摘要

Background and AimsThe taxonomic complexity of Crataegus (hawthorn; Rosaceae, Maleae), especially in North America, has been attributed by some to hybridization in combination with gametophytic apomixis and polyploidization, whereas others have considered the roles of hybridization and apomixis to be minimal. Study of the chemical composition and therapeutic value of hawthorn extracts requires reproducible differentiation of entities that may be difficult to distinguish by morphology alone. This study sought to address this by using the nuclear ribosomal spacer region ITS2 as a supplementary DNA barcode; however, a lack of success prompted an investigation to discover why this locus gave unsatisfactory results.