作 者 ：Fang Zhen-Fu
期 刊 ：植物分类学报 1987年 4期
Keywords:Salix, Distribution, Origin,
Abstract:
1. The distribution of Salix species among the continents. There are about
526 species of Salix in the world, most of which are distributed in the Northern Hemisphere
with only a few species in the Southern Hemisphere. In Asia, there are about 375 species, mak-
ing up 71.29 percent of the total in the world, including 328 endemics; in Europe, about 114
species, 21.67 percent with 73 endemics; in North America, about 91 species, 17.3 percent with
71 endemics; in Africa, about 8 species, 1.5 percent, with 6 endemics. Only one species occurs
in South America. Asia, Europe and North America have 8 species in common (excluding 4
cultivated species). There are 34 common species between Asia and Europe, 14 both between
Europe and North America and between Asia and North America, 2 between Asia and Africa.
Acording to the Continental Drift Theory, the natural circumstances which promoted speciation
and protected newly originated and old species were created by the orogenic movement of the
Himalayas in the middle and late Tertiary. Besides, the air temperature was a little higher in
Asia than in Europe and North America (except its west part) and the dominant glaciers were
mountainous in Asia during the glacial epoch in the Quaternary Period. Then willows of Eu-
rope moved southwards to Asia. During the interglacial period they moved in opposite direc-
tion. Such a to-and-fro willow migration between Asia and Europe and between and North
America occurred so often that it resulted in the diversity of willow species in Asia. Those
species of willows common among the continents belong to the Arctic flora.
2. The multistaminal willows are of the primitive group in Salix. Asia has 28 species of
multistaminal willows, but Europe has only one which is also found in Asia. These 28 species
are divided into two groups, “northern type” and “southern type”, according to morphology of
the ovary. The boundary between the two forms in distribution is at 40°N. The multistami-
nal willows from south Asia, Africa and South America are very similar to each other and
may have mutually communicated between these continents in the Middle or Late Cretaceous
Period. The southern type willows in south Asia are similar to the North American multista-
minal willows but a few species. The Asian southern type willows spreaded all over the conti-
nents of Europe, Asia and North America through the communication between them before the
Quaternany Period. Nevertheless, it is possible that the willows growing in North America
immigranted through the middle America from South America. The Asian northern type mul-
tistaminal willows may have originated during the ice period.
The multistaminal willows are more closed to populars in features of sexual organs. They
are more primitive than the willows with 1-3 stamens and the most primitive ones in the ge-
nus.
3. The center of origin and development of willows Based on the above discussion it is re-
asonable to say that the region between 20°-40°N in East Asia is the center of the origin and
differentiation of multistaminal willows. It covers Southern and Southwestern China and nor-
thern Indo-China Pennisula.