Ploidal levels in the arctic-alpine polyploid Draba lactea (Brassicaceae) and its low-ploid relatives

Ploidal level information is of particular importance in intricate polyploid complexes such as in arctic-alpine Draba. Relative DNA content is reported for the tetra- and hexaploid D. lactea and seven of its low-ploid relatives. Flow cytometry was used to study 200 plants from 93 populations, the screening based on relative fluorescence. Absolute DNA content was determined by Feulgen densitometry for 13 plants from seven species, and reference chromosome numbers were determined in 12 plants (1-3 per species) representing six species. The plants grouped into diploids (2n = 16), tetraploids (2n = 32), hexaploids (2n = 48), and two triploids. Each ploidal level showed a linear increase in relative DNA content, pointing to a relatively recent polyploid origin. The diploid level was confirmed in D. nivalis, D. subcapitata, D. fladnizensis, and D. lonchocarpa. Draba palanderiana, reported previously as di-, tetra- and octoploid, was diploid in all investigated accessions. Hexa- and tetraploids were observed in D. lactea, in approximately the same ratio (8: 1) as reported previously. The ploidal levels of the Central Asian D. altaica and D. turczaninovii are reported here for the first time as diploid and tetraploid, respectively. (c) 2005 The Linnean Society of London.