The diploid nature of the Chilean Epipetrum and a new base number in the Dioscoreaceae

Abstract

Chromosomal analyses were conducted for the first time in all three species of the Chilean endemic Epipetrum Phil. (Dioscoreaceae; the yam family). Mitotic chromosome counts showed that all studied individuals of the rare Epipetrum bilobum and E. polyanthes, and most studied individuals of the more widespread E. humile, had 2n = 14 chromosomes. However, two populations of E. humile had 2n = 28 chromosomes. The ideograms shared a similar karyotype constitution for the three species but with a duplicated chromosome number in some populations of E. humile. Our results suggest that the Epipetrum taxa are mainly diploids, with a base number of x = 7, and the tetraploid cytotypes have arisen only in few cases. After that of Borderea (x = 6), this chromosome base number is the second lowest one found in the Dioscoreaceae. Epipetrum and Borderea are two small, relict, satellite genera of the Dioscoreaceae, endemic to Chile (South America) and the Pyrenees (Southwestern Europe), respectively. The two taxa share several morphological attributes and are adapted to rocky and mountain habitats. However, whereas Borderea is an allotetra‐ploid genus of relatively recent hybrid origin, Epipetrum is diploid in common with the species found in the early branching clades of Dioscorea.