Cytological studies on some representative species of the tribe Orchideae (Orchidaceae) from China

Cytological studies were carried out on 14 taxa belonging to Amitostigma, Chusua, Galearis, Habenaria, Hemipilia, Hemipiliopsis, Herminium, Peristylus and Ponerochis, collected mostly from the south-eastern part of the Hengduan Mountain Region, south-west China. Cytological data on 11 of the taxa are reported for the first time. The interphase nuclei were either of the simple chromocentre type or intermediate between simple and complex chromocentre types. The nuclear morphology of Hemipiliopsis at interphase supports the conclusion that it is related more closely to Chusua and Ponerochis than to Habenaria. At the whole tribe level, however, the results did not indicate a clear correlation between morphological features of the interphase nuclei and phylogeny. The somatic chromosome numbers were 2n = 42 in ten species and 2n = 32, 38, 40, 64 and 72 in four species. The chromosome counts of 2n = 32 and 64 in Habenaria aitchsonii are rare in the genus. It is proposed that the repeated change of chromosome number from x = 7 to x = 8 has played an important role in the evolution of the tribe Orchideae. This change has occurred mainly in the European subtribe Orchidinae, but also in the Asian subtribe Habenariinae. (C) 2004 The Linnean Society of London.