New Chromosome Counts of Some Dicots in the Sino-Japanese Region and Their Systematics and Evolutionary Significance

Abstract

Abstract:

New somatic chromosome numbers for nine species eight families and eight gen

era in the Sino-Japanese Region are reported here as shown in Table 1. Data of six genera

are previously unknown cytologically. The bearings of these new data on the systematics

and evolution of the related species, genera or families are discussed as follows: (1) Platy-

carya strobilacea Sieb. et Zucc. (Juglandaceae). The chromosome number of this species is

2n=24, with a basic number of x=12, which deviates from 2n=32 occurred in Juglans,

Carya, Pterocarya and Engelhardtia with the basic number x= 16. The Juglandaceae ap-

pears to be fundamentally paleotetraploid, with an original basic number of x = 6 in Platy-

carya and x-8 in the other four genera, although secondary polyploidy occurs in Carya.

Based on the remarkable morphological differences between Platycarya and the rest seven

genera of the family, Manning (1978) established two subfamilies: Platycaryoideae for

Platycarya and Juglandoideae for the other genera. Iljinskaya (1990), however, recently

established a new subfamily: Engelhardioideae for Engelhardtia. Lu (1982) points out that

because of a great number of primitive characters occurring in Platycarya, the genus could

not be derived from any other extant juglandaceous taxa but probably originated with the

other groups from a common extinct ancestor. The present cytological data gives support to

Manning′s treatment. We are also in favor of Lu′s supposition and suggest that basic aneu-

ploid changes, both ascending and descending, from a common ancestor with the original

basic number x=7, took place during the course of early evolution of the Juglandaceae and

led to the origin of taxa with x=6 and 8. Subsequent polyploidy based on these diploids oc-

curred and brought forth polyploids of relic nature today, whereas their diploid progenitors

apparently have become extinct. (2) Nanocnide pilosa Migo (Urticaceae). The chromo-

some number of this Chinese endemic is 2n-24, with a basic number of x=12. An aneu-

ploid series occurs in the Urticaceae, with x--13, 12, I1, 10, 9, 8, 7, etc. According to

Ehrendorfer (1976), x = 14, itself being of tetraploid origin, is the original basic number of

the whole Urticales, and descending aneuploid changes took place in the early stage of evolu-

tion of the Urticaceae and Cannabinaceae. In addition to Nanocnide, x= 12 also occurs in

Australina, Hesperonide and Lecanthus, and partly in Chamabainia, Elatostema, Girardinia,

Pouzolzia and Urtica. (3--4) Sedum sarmentosum Bunge and S. angustifolium Z. B. Hu

et X. L. Huang (Crassulaceae). The former is a member of the Sino-Japanese Region,

while the latter is only confined to eastern China. The chromosome number of Sedum is re-

markably complex with n=4-12, 14-16…74, etc. S. angustifolium with 2n=72 of the

present report is evidently a polyploid with a basic number of x =18 (9^?) Previous and pre-

sent counts of S. sarmentosum show infraspecific aneupolyploidy: n = c. 36 (Uhl at al.

1972) and 2n=58 (the present report). These two species are sympatric in eastern China

and are morphologically very similar, yet distinguishable from each other (Hsu et al. 1983)

S. sarmentosum escaped from cultivation in the United States gardens exhibited high irregu-

larity in meiosis (Uhl et al. 1972). Uhl (pets. comm. ) suspected strongly that it is a high-

ly sterile hybrid. R. T. Clausen (pets. comm.) found that plants of S. sarmentosum natu-

ralized in the American Gardens propagated by means of their long stolons and broken stem

tips, and could not yield viable seeds. Hsu et al. (1983) found that some of the plants of S.

sarmentosum and S. angustifolium did yield a few seeds, but other did not. These species

are, therefore, by the large vegetatively apomictic. (5) Glochidion puberum (L. ) Hutch.

(Euphorbiaceae). The genus Glochidion includes about 300 species, but only eigth species

from the Himalayas have been studied cytologically, with n= 36 and 2n= 52, having a basic

number of x= 13. The present count for the Chinese endemic G. puberum establishes the

tetraploid chromosome number 2n= 64, and adds a new basic number x= 16 to the genus.

(6) Orixa japonica Thunb. (Rutaceae). Orixa is a disjunct Sino-Japanese monotypic

genus. Out of the 158 genera of the Rutaceae, chromosome numbers of 65 genera have

hitherto been investigated, of which 42 genera are with x=9 (66.61%), some with x=7,

8 and 10, and rarely with x=13, 15, 17 and 19. The present count of 2n=34 for O.

japonica may have resulted from a dibasic tetraploidy of n=8+9. (7) Rhamnella frangu-

loides (Maxim.) Weberb. (Rhamnaceae). The chromosome number of this member of the

Sino-Japanese Region is 2n= 24. with a basic number of x= 12. The basic number x= 12

also occurs in Hovenia, Paliurus, Sageretia, Ceanothus and Berchemia. Hong (1990) sug-

gested that x= 12 in Rhamnaceae may be derived from descending aneuploidy of a paleote-

traploid ancestor. (8) Sinojackia xylocarpa Hu (Styracaceae). The chromosome number of

this rare Chinese endemic is 2n= 24, with a basic number of x =12, which is identical with

that in Halesia and Pterostyrax, but deviates from that in Styrax (x=8). The basic num-

ber x=8 in the Styracaceae may be derived from the original basic number x=7 by ascend-

ing aneuploidy in the early stage of evolution of the family, and x=12 may be derived from

polyploidy. (9) Thyrocarpus glochidiatus Maxim. (Boraginaceae). The chromosome num-

ber of this Chinese endemic species is 2n=24, with a basic number of x=12. An extensive

aneuploid sequence of x = 4-12 occurs in the Boraginaceae, of which x = 8, 7 and 6 are the

most common. The basic number x=12 also occurs in Cynoglossum and Mertensia. It is evi-

dent that aneuploid changes, both descending and ascending, from an ancestor with x = 7,

have taken place in the primary phase of evolutionary diversification of the Boraginaceae,

and subsequent polyploidy has given rise to x=15, 17 and 19 in a few genera (e. g. Amsin-

skia and Heliotropium). The origin of x=12 is not certain. Either it be a result of ascending

aneuploidy, or a product of polyploidy on the basis of x = 6. The present authors are in favor

of the latter.

Key words: New chromosome counts, Dicotyls, Sino-Japanese Region

Hsu Ping-sheng, Weng Ruo-feng, Siro Kurita. New Chromosome Counts of Some Dicots in the Sino-Japanese Region and Their Systematics and Evolutionary Significance[J]. .

New Chromosome Counts of Some Dicots in the Sino-Japanese Region and Their Systematics and Evolutionary Significance

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