中国独活属的核型研究

本文首次报道了我国独活属10种(含1变种)的核型，其中8种的染色体数目亦为首次报道。研究表明它们的染色体数目均为2n＝2x＝22，为二倍体，其核型为中部着丝点和亚中部着丝点染色体组成，仅具1A和2A两种类型。有4种具随体染色体，在部分H．vicinum植株中发现有1条B染色体，在H．millefolium var．longilobum中同时存在2n＝22和2n＝24的非整倍体．不同种的染色体形态不同，为分类研究提供了细胞学依据。 本文在核型分析基础上讨论了该属分类群的划分、种间亲缘关系及演化，并结合我国毗邻地区该属细胞学资料和地理分布规律，提出我国西南部的横断山区是独活属的频度中心和多样性中心。

STUDIES ON KARYOTYPES OF THE GENUS HERACLEUM FROM CHINA

The present paper reports the chromosome numbers and karyotypes of nine species and one variety of Heracleum in the Hengduan Mountains of South-western China. Among them the somatic chromosome number and karyotypes of seven species and one variety are reported for the first time. Their chromosome parameters and karyotypes formulae are shown in Tables 1, 2, and their karyotypes and idiograms are shown in Plates 1, 2 and Fig. 1. The chromosome number of all the species is 2n=2x = 22 except H. millefolium var. langilobum, which has both 2n=22 and 2n=24 (see Plate 2: T-W). The karyotypes of the nine species and one variety of Heracleum consist of metacentric and submetacentric chromosomes. The karyotypes of two species, H. wolongense and H. stenopterum, belong to "1A, type, while the karytypes of the rest belong to "2A" type in Stebbins' classification. Four species have two chromosomes with satellites. And one B - chromosome is discovered in somatic cells of some H. vicinum individuals (see Plate 1: G). Classification is discussed based on the analysis of the chromosome number and kary-otype of Heracleum. The cytotypes are found different between H. millefolium var. millefolium and H . mille folium var . langilobum . The karyotypic formula of the former one is K(2n) =22=18m 4sm, whereas that of the latter is K (2n) = 22 = 16m 6sm and K (2n) = 24=18m 6sm. They also differ from one another in order number of the sub-metacentric chromosomes. Although they are small low-growing plants and have 3-4 pin-natipartite leaves and seem closely related, they differ greatly in length and density of arrangement of the ultimate lobelets and in indumentum of ovaries. Under SEM, the sculpture pollen exine is shown differentiated between the two varieties. Hence it is suggested that H. millefolium var. longilobum be treated as an independent species. Furthermore, based on the interspecific relationship and variation in chromosome number and karyotypic symmetry, the hypothesis is proposed that the genus Heracleum has been evolving in two directions, from diploid to polyploid and from symmetrical to asymmetrical in karyotype. Finally, according to the data available the correlation is found between the change of chromosome number and karyotypic symmetry on one side and the latitudinal distribution of the genus on the other, as 26 species and one variety of Heracleum occur in the Hengduan Mountains, and their external morphological characters and cytotypes have differentiated distinctly, it is considered that the Hengduan Mountains is both the center of frequency and the center of diversity of Heracleum. Moreover, we speculate that the Hengduan Mountains or the Caucasus is the original center of this genus.