杜鹃属的系统发育与进化

本文以形态学为基础,结合一些新的有关资料,如解剖学、细胞学、化学等方面的证据讨论了杜鹃属的系统发育与进化问题,认为常绿杜鹃亚属在本属系统发育中处于原始地位,其中的云锦杜鹃亚组、耳叶杜鹃亚组、大叶杜鹃亚组和杯毛杜鹃亚组等4个亚组是原始类群,也即是其祖先的直接后裔。本属的原始祖先是具常绿习性,各部无毛(也无鳞片),花部不定数,具复合三叶隙构造的乔木,即类似现存原始类群的植物,它们生长于白垩纪至早第三纪古北大陆南缘,大约在我国西南部的热带山区森林环境中。随着地史的变迁,杜鹃属在漫长的进化过程中平行进化和发展为两个进化枝,一枝分化成各部被鳞片的热带附生类群或高山类群(包括4个亚属),另一枝演变为多少被毛的温带林下的半常绿至落叶类群(3个亚属),有鳞的髯花杜鹃组及落叶的日本马银组和落叶杜鹃组是两个进化枝演化上的高级类群。

THE PHYLOGENY AND EVOLUTION OF GENUS RHODODENDRON

In order to study the phylogeny and evolution of genus Rhododendron, we detail six problems as follows: 1. The problems of classification and system of Rhododendron are discussed and the recent articles by H. F. Copeland (1943) , H. A. Seithe (1960, 1980) , M. N. Philipson and W. R. Philipson (1986) are also reviewed. We believe that the system proposed by H. Sleumer (1949) is a natural system. 2. The systematic position of Rhododendron is recognized as a representative original genus in phylogenetic process of the family Ericaceae. 3. From the habit and the characters of leaf anatomy, indumentum, vascularization of nodes (or leaf trace) , and the positon of the flower buds on a stem, inflorescence types, corolla forms, the numbers of corolla lobs and stamens as well as ovary locales, seed types, the numbers of chromosome etc., the evolutional tendencies of those morphology and anatomy are discussed. 4. The evolutionary relationships among subgenera of Rhododendron are showed in this paper. Based on the morphological characters and some recent studies such as anatomy, cytology, chemistry etc. have demonstrated that the phylogeny of this genus are evidential. It can be regarded that the Rhododendron with evergreen tree, glabrous and elepidote, the numbers of flower parts indefinite and with comples trilacunar node are the ancestral group. The subgenus Hymenanthes apparently represents a primitive state in this genus. Among those subsect. of subgenus Hymenanthes, the subsect. Fortunea, Auriculata, Grandia, Falconera are the primitive groups or can be regarded as the descendents of ancestor of this genus. Closely associated with the change of historical geological periods two large branches nearly parallelly evolved from this genus. The one has been developed into the lepidote tropical epiphytes and alpine taxa, including the 4 subgen.: Rhododendron, Pseudazalea,Pseudorhodorastrum and Rhodorastrum, the another one into the taxa which are more or less haired, semi-evergreen or deciduous under temperate forest, including the 3 subgen... Azaleastrum, Tsutsusi, Pentanthera. 5. Two problems are discussed on three phylogenetic stage of development and evolutionary directions in each taxa of this genus. All of these phenomena closely associated with the great changes of environmental conditions. 6. Phylogeny of Rhododendron reflects the vicissitudes of paleogenic geology and climate, namely, closely related to the evolution of palleogcographical environment. The plants of Rhododendron were originated from south margin of Laurasia in late Cretaceous time, probably under forest environment in the tropical mountains of southwestern China.