Hsu Ping-sheng, Weng Ruo-feng, Siro Kurita
1994, 32 (5): 411–418
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) Platycarya 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 appears to be fundamentally paleotetraploid, with an original basic number of x = 6 in Platycarya 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 aneuploid 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 occurred and brought forth polyploids of relic nature today, whereas their diploid progenitors
apparently have become extinct. (2) Nanocnide pilosa Migo (Urticaceae). The chromosome number of this Chinese endemic is 2n-24, with a basic number of x=12. An aneuploid 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 evolution 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 remarkably 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 present 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 irregularity in meiosis (Uhl et al. 1972). Uhl (pets. comm. ) suspected strongly that it is a highly sterile hybrid. R. T. Clausen (pets. comm.) found that plants of S. sarmentosum naturalized 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 franguloides (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) suggested that x= 12 in Rhamnaceae may be derived from descending aneuploidy of a paleotetraploid 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 number x=8 in the Styracaceae may be derived from the original basic number x=7 by ascending 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 number 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 evident 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. Amsinskia 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 favorof the latter.