Genome Size in South American Gentianella (Gentianaceae, Swertiinae), with a Special Emphasis on Species from the Bolivian and Ecuadorian Andes

The subcosmopolitan genus Gentianella Moench (Gentianaceae, Swertiinae), with more than 170 currently accepted species in South America alone, is one of the emblematic examples of major and rapid radiations in the Andes. However, the taxonomy of South American Gentianella is far from being resolved. Over a century has passed since the publication of the last comprehensive treatment by Ernst Gilg in 1916. Using flow cytometry, the genome size of 115 accessions of 39 species, of which 37 were from South America, was measured, with the objective to assess the taxonomic utility of that trait. Also, the relationships of genome size with environmental factors such as mean annual temperature and precipitation, as well as the life history traits, habit, reproduction, habitat, and elevational belt were examined. The genome size values of the investigated South American accessions fell into two size classes, ranging from 2C = 7.60 pg to 11.30 pg and from 2C = 16.54 pg to 18.34 pg. The latter size class contained only accessions of G. briquetiana (Gilg) T. N. Ho & S. W. Liu. These accessions, and a further one of G. limoselloides (Kunth) Fabris with an intermediate value of 2C = 14.71 pg, were inferred to be octoploid. Genome size was not correlated with temperature, precipitation, habit, or elevational belt. By contrast, significant differences in genome size between groups were found regarding habitat and reproduction. Furthermore, genome size of one of the informal taxonomic groups of Gilg (Barbatae) differed from that of the remaining groups. However, this finding is of doubtful taxonomic relevance because of inconsistencies in the application of Gilg’s defining criterion of Barbatae, i.e., the presence of trichomes inside the corolla tube. Based on the overall results, it is concluded that genome size is not a taxonomically useful trait in South American Gentianella. Still, the data offer a first view on genome size variation and evolution in this diverse but poorly studied group.