Abstract:A morphological and cytological study of a population of Ophioglossum petiolatum Hook. from the vicinity of Kunming, Yunnan Province was carried out. The fronds of this species are very variabte in. either size or figure. The outlines of laminae of different plants vary from narrowly lanceolate to ovate or broadly ovate (length: breadth can be from 6:1 to 1:1). The apices of laminae range from taper-pointed to acute or blunt, and the bases of laminae from attenuate to cuneate or nearly truncate. In most cases, the spore mother cells of the species have 480 bivalents at pro-meta- phase I of meiosis. The spores produced after normal meiosis are seemingly available. It shows that the species is an octoploid and probably sexual In few plants, many univalents at metaphase I of meiosis have also been seen, but we have failed to count their exact chromosome numbers. However, it reveals that there is a second cytotype in the population. From the fact that O. petiolatum has the great morphological variability and approximately constant chromosome number in a single population, the ecological conditions may not be the main reason of morphological variations of the Species. The high level of polyploidy and probable inbreeding system, the subterranean gametophytes must be hard to outcross, may give it a great ability of genetic lead which increases the genetic heterogeneity. and morphological varibility of populations. The voucher specimens are deposited inthe Herbarium of our Institute (PE). I am grateful to Prof. W. M. Chu of Yunnan University for his helpful suggestion and discuss.