Karyomorphology and evolution in some Hamamelidaceae and Platanaceae (Hamamelididae; Hamamelidales)

Abstract

Karyomorphology in 14 species of 12 genera representing a variation of Hamamelidaceae and in one species of Platanaceae (Platanus only) is investigated in an effort to contribute to an understanding of chromosome evolution and inter- and intrafamilial relationships. All genera investigated show similar chromosome features at resting stage and prophase, excepting that at resting stageRhodoleia shows the simple, rather than the simple-complex, chromocenter type as in other genera. At metaphase all the genera investigated of Hamamelidaceae, like other ‘lower’ Hamamelididae, have chromosomes with median centromeres (m-chromosomes), those with submedian centromeres (sm-chromosomes) and those with subterminal (or terminal) centromeres (st-t-chromosomes) at different frequencies, although frequencies ofst-t-chromosomes are always less than 33%. InPlatanus,m-chromosomes are lacking and insteadst-t-chromosomes are predominant (86%), a feature seemingly very specialized. We confirmedx=7 in Platanaceae,x=12 in Hamamelidoideae and Rhodoleioideae, andx=8 in Exbucklandioideae and Altingioideae (Hamamelidaceae). An analysis of chromosome morphology supports the hypothesis thatx=12 in the former two subfamilies is of tetraploid origin fromx=6, rather than of triploid origin fromx=8. We further give brief comments on the suprageneric classification of Hamamelidaceae that was recently proposed by Endress.