Genome size and pollen viability as taxonomic criteria: Application to thegenus Hosta

Genome size (C values) and pollen viability staining were applied as new cr iteria to investigate the taxonomy of the genus Hosta Tratt. (Hostaceae). N early all species of the genus Hosta have the same basic chromosome number (2n = 2x = 60). However, the nuclear DNA contents, as measured by flow cyto metry with propidium iodide, could be demonstrated to range between 17.2 to 26.6 pg. This implies that the largest genome contains roughly 10(10) more base pairs than the smallest. Therefore, nuclear DNA content is a very rel evant taxonomic trait that can be measured simply by flow cytometry. In add ition, differences in overall DNA composition were demonstrated by comparin g to DAPI fluorescence. In general, genome size data confirmed the division into three subgenera. The geographical distribution of genome sizes indica tes the migration pattern of Hosta throughout East Asia. The species belong ing to the mainly Korean subgenus Bryocles, with a low nuclear DNA content (17.2-19.3 pg), can now largely be distinguished from the mainly Japanese s pecies of the subgenus Giboshi (21.3-26.5 pg). The exception is H. longissi ma, that with only 19.6 pg provides a nice example of a decrease in DNA con tent. On the mainland, as well as on Honshu, species with increased and dec reased DNA content have evolved independently. The usefulness of pollen via bility to detect hybrids in Hosta was demonstrated in a large series of art ificial crosses between bona fide species. Consequently, pollen viability w as measured in all available Hosta described as species. Several had low po llen viability and were concluded to be hybrids. Morphology and DNA content confirmed this in most cases. The resulting 23 species approximate the num ber of Hosta species that follows from the combined studies by Fujita (1976 ([18])) on the Japanese species and Chung (1991 a([11])) on the Korean spec ies.