柳树起源与进化的探讨

On the Origin and Evolution of the Willows

柳树(杨柳科柳亚科)具有3个属、约450个天然种(以及大量的天然杂种),自然分布于大约从南纬52度至北纬82度从海平面附近至海拔5 000 m左右从南温带到北寒带的非洲、南美洲、亚洲、欧洲和北美洲(大洋洲和南极洲无自然分布的柳树),即原柳属(约50种,大致产于北极圈以南的地区)、钻天柳属(约3种,产于鄂霍次克海和日本海的四周地区)和柳属(约400种,大致产于北回归线以北的地区)。从原始被子植物到当代柳树,显然是经历了一个漫长而曲折的演化历程。古柳群可能大约在白垩纪中期起源于西冈瓦纳古陆,并在广为扩散至各地的过程中沿着不同方向进一步演化发展,而前面提及的3个属则为其现存的后裔。原柳属可能大约在白垩纪晚期发生于西冈瓦纳古陆的非洲;先放射分布于古陆本土(后来又因古陆的分裂而分别存在于非洲大陆、马达加斯加岛和南美洲),后逐步扩散至劳亚古陆;统一的劳亚原柳属植物区系又因欧亚陆块与北美陆块的完全分离而被分割为各自独立发展的两个部分。钻天柳属很可能是在第三纪晚期发生于欧亚陆块的东北部。柳属可能大约在第三纪中、晚期发生于古地中海东部地区,后逐步散播于欧亚陆块,并经过白令地区迁移至北美。文中提供了有关植物的属、种一览,包括它们的正确名称、文献引注、地理分布等。

The willows （Salicaceae subfam. Salicoideae） are composed of three genera with about four hundred and fifty natural species （as well as a great number of natural hybrids） and distribute naturally in Africa,South America,Asia, Europe et North America （not in Oceania and Antarctica） from about 52 degrees south latitude to 82 degrees north latitude et from near sea level to altitude more than 5 000 m et from the south temperate zone to the north frigid zone . i. e. Pleiarina of about fifty species and approxi- mately on the south of the Arctic Circle, Chosenia of about three species and in the neighbouring areas of both the Sea of Ochotsk et the Sea of Japan, and Salix of about four hundred species and roughly on the north of Tropic of Cancer. It is quite evident that there is a long and tortuous evolutionary process from primitive angiosperm to the contemporary willows. Archaic willow group probably originated from the West Gondwanaland during the Middle Cretaceous and then evolved further along the various direction in the course of its spreading everywhere; and the three genera before-mentioned are its extant descendants. The genus Pleiarina possibly occurred in Africa of the West Gondwanaland during the Late Cretaceous ; it first radially scattered over this locality （and it existed in Africa, Madagascar and South America respectively owing to the breakup of the archaic land afterward） and then spread to the Laurasia; subsequently ,the unitary Laurasia＇s Pleiarina flora was divided into two parts developing alone because of wholly separating each other of the Eurasia land mass and the North America land mass. The genus Chosenia most likely a- rose in the northeastern Eurasia land during the Late Tertiary. The genus Salix might emerge from eastern Tethys regions during the Middle and Upper Tertiary,and then widely spread in Eurasia land et progres- sively migrated to North America land via Bering regions. Besides, a conspectus of all the genera and spe- cies of the plants concerned is provided in this paper, including their correct names, bibliographic refer- ences, geographic distributions etc.