作 者 ：Li Lin-Chu
期 刊 ：植物分类学报 1988年 5期
Keywords:Taxodium, Karyotype, Cytogeography,
Abstract:
The present paper deals with the karyotypic analysis of Taxodium ascendens Brongn.
The somatic chromosomes in root-tip cells of the plant are found to be 2n =22, all with median
and submedian constrictions. A character of the karyotype is that the chromosome 10 has
a long kinetochore region (Plate 1:1). According to the terminology defined by Levan et al.[18],
the karyotype formula is k(2n)=22=20m+2sm, which is different to Huang et Hsu’s[8]
K(2n)=24=22m+2B(m). The karyotype belongs to “lA” of Stebbins’[24] karyotypic symmetry
and is generally regarded as a relatively primitive one. The species’ chromosome complement
is 2n=22=2L+8M2+12M1 according to I.R.L.difined by Kuo et al.[15] based on relative length.
The lengths, arm ratios and types of chromosomes of the species are given in Table 1-I. The
morphology of the chromosomes and the karyotype, are given in Plate 1:1.
In the light of the works of Schlarbaum et al.[21] and Mehra et al.[17], K(2n)=22=20m
(2SAT)+2sm and 2n=22=2L+6M2+14M1 are for T. distichum (L.) Rich. (see Table 1-II),
K(2n)=20m+2sm and 2n=22=4L+4M2+12M1+2S for T. mucronatum Tenore (see Table
1-III, Plate 1:2), which belong to “lA” and “2A” respectively.
The differences between three species in the ratio of the longest to the shortest chromosome,
I.R.L. and the proportion of chromosomes with arm ratio >2 show that the karyotype of T.
mucronatum is the most advanced and that of T. distichum the most primitive. The present
author suggests that the sequence of evolutionary advance be T. distichum, T. ascendens, T. mu-
cronatum.
Based on the evidence from the karyotype analyses, ecology and geographical distribution
(including fossil), the secondary center of genetic diversity (Fig. 1) and the probable evolu-
tionary pattern (Fig. 2) of Taxodium are discussed.