The Studies on the Karyotypes and Cytogeography of Taxodium Rich.(Taxodiaceae)

Abstract

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.

Key words: Taxodium, Karyotype, Cytogeography

Li Lin-Chu. The Studies on the Karyotypes and Cytogeography of Taxodium Rich.(Taxodiaceae)[J]. .

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The Studies on the Karyotypes and Cytogeography of Taxodium Rich.(Taxodiaceae)

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