Abstract
Background The genus Taraxacum F.H. Wigg. (fam. Compositae, subfam. Liguliflorae) includes about 300 species globally. Seventy-nine are widely distributed throughout China, mostly in southwestern and northwestern regions. The genus has adopted different reproductive strategies, and there is weak reproductive isolation and differentiation between species. Unresolved species boundaries make classification and identification of Taraxacum species is difficult. Taraxacum germplasm resources in northeastern China are not current and therefore, do not accurately reflect actual distribution. The objective of this study was to investigate the morphological traits of Taraxacum species distributed in northeastern China and identify those that will facilitate classification of Taraxacum species in this region.Methods Leaf, flower, and achene characteristics of 18 species were used for morphological classification. Scanning electron microscopy was used to examine pollen morphology. Leaf extracts were analyzed by high performance liquid chromatography to measure the caffeic acid, chlorogenic acid, and luteolin content. Internal transcribed spacer (ITS) sequences were used to determine the sequence pairwise differences among the species and their utility in delimitation.Results The taxa were classified into groups based on morphology. Beak length to achene length ratio was a new taxonomically informative morphological trait for delimitation. The ITS sequence analysis supported the classification of the taxa, but genetic distances among the taxa did not reflect morphological differences. Phylogenetic analysis resolved the eighteen species into three groups. Group I: T. coreanum, (which has white flowers). Group Ⅱ: T. heterolepis, T. sinomongolicum, T. variegatum, T. asiaticum, T. lonchophyllum, T. falcilobum, T. brassicaefolium, and T. erythropodium. Group Ⅲ: T. formosanum, T. liaotungense, T. mongolicum, T. borealisinense, T. ohwianum, T. platypecidum, T. urbanum, T. antungense, T. asiaticum, and T. junpeianum. The chemical composition of the species is not suitable for their delimitation; T. antungense is a potential medicinal plant with therapeutic properties since it had the highest concentration of phytochemicals.Conclusions This study completes the classification and delimitation of the Taraxacum germplasm resources present in northeastern China and supplements the "Flora of China". The study thus provides information that will help to further develop Taraxacum medicinal resources and regulate Taraxacum medicinal use in traditional Chinese medicine.