Cytological studies on the genus Holcoglossum (Orchidaceae)

Abstract

The karyotypes of ten species of Holcoglossum (Orchidaceae), a highly endangered and diversified genus from China, were investigated to study the infrageneric relationships, biogeography, and speciation patterns in the Hengduan Mountains. The karyotype formulae of the studied species are as follows: 2n = 38 = 20m + 18sm in H. subulifolium, 2n = 38 = 22m + 16sm in H. amesianum, 2n = 38 = 26m + 12sm (6 SAT) in H. lingulatum, 2n = 38 = 26m + 12sm in H. wangii, 2n = 38 = 10m + 28sm in H. kimballianum, 2n = 38 = 14m + 22sm + 2st in H. flavescens, 2n = 38 = 24m + 12sm + 2st in H. rupestre, 2n = 38 = 14m + 20sm + 4st in H. sinicum, 2n = 38 = 16m + 14sm + 8st in H. weixiense, and 2n = 76 in H. tsii. The karyotypes of two tropical species, H. amesianum and H. subulifolium, are the most primitive in the genus, whereas those of four temperate alpine species, H. sinicum, H. rupestre, H. weixiense, and H. flavescens, are more advanced. H. tsii is a tetraploid and H. rupestre may be one of its ancestors. The low frequency of polyploidy in Holcoglossum in the Hengduan Mountains region supports the conclusion that chromosome stasis during rapid speciation is common there. © 2007 The Linnean Society of London.