A morphometric comparison of three closely related species of Gentiana (Gentianaceae), endemic to the region of the Qinghai–Tibet Plateau

Gentiana section Cruciata (Gentianaceae) is mainly found on alpine mountains across Eurasia, with the greatest species diversity occurring on the Qinghai–Tibet Plateau. Gentiana crassicaulis Duthie ex Burk. and the closely related species Gentiana robusta King ex Hook. f. and Gentiana tibetica King ex Hook. f. in sect. Cruciata show extremely high morphological similarity, which could be one of the main reasons for their misidentification. This study targets the authentication of the three closely related species in section Cruciata using morphometric analysis of flower shape. We collected 130 individuals in 14 populations of G. crassicaulis, 38 individuals in 12 populations of G. tibetica, and 45 individuals in 13 populations of G. robusta throughout the respective geographical ranges of the species. We used the parameters for bract length (l1), bract width (w1), inflorescence circumference (c), inflorescence width (w2), calyx length (l2), and corolla length (l3) to quantify the flower shape. The analyses showed that the parameters Rb (l1/w1), Ri (w1/w2), and l3 were significantly different between two of the species: G. crassicaulis and G. tibetica could be identified through corolla length, and although very similar to G. crassicaulis and G. tibetica, G. robusta is distinguishable using the parameters Rb and Ri.