中国第三纪植被和植物区系历史及分区

被子植物的发展(或称辐射)是与古气候、古地理环境密切相关的，诸因素的变化相互影响及制 约，形成植物发展的阶段性。这种阶段变革及划分与传统的地质时代划分——断带，不尽一致，因而讨论 植物地理分区问题应以发展的不同阶段为基础，致使分区更为合理。     在晚白垩纪中晚期，被子植物已成为植物区系中的优势成分，从它出现以来的发展演化大致可划分 为四个阶段：(1)初始期  被子植物初次出现，具有叶形小、叶边全缘、叶脉缺乏规律性、脉级分化程度低 等原始性特点，同时在区系中的种数及个体数量均为极少数，此时大约在早白垩纪的中晚期；(2)极盛时 期被子植物发展具有一定规模至占绝对优势，此时叶形增大，叶脉有了规律性，脉级分化逐渐完善，在 植物区系中所占比例达40％一60％，以致占绝对优势，主要科属出现了，时间在晚白垩至老第三纪；(3) 草本植物繁盛阶段  由于在新第三纪时气候逐渐转凉，早期的一些木本植物消灭了，以草本植物渐增多 至大量扩散为特点，时间约在中新世至上新世；(4)第四纪阶段  此时我国由于山岳冰川随全球性气候 冷暖变化而进退，影响植物的分布及发展，植物区系的总面貌与现代接近或略有差别。   本文亦重点讨论了植物发展的第二、第三阶段的植物地理分区。

The Tertiary Vegetation and Flora and Floristic Regions in China

The development or adaptation radiation of angiosperms has been closely related to the paleoclimate and paleoenvironment. Several environmental factors, influencing each other, have affected the evolution or development of angiosperms, which falls into different stages. The lines between these stages are not consistent with the traditional geological ages. Floristic regionalization might be better based on the stages of the development.      Angiosperms have become important or dominant elements in the flora since the middle and late period of the Late Cretaceous. The development of angiosperms may be divided into four stages: (1) Initial stage: The angiosperms were not yet well established during the Early Cretaceous. The number of species and individuals was limited, the leaf small, mostly with en- tire margine, irregular venation and poor differentiation of venation; (2) Flourished stage: The angiosperms increased dramatically and became abundant. The leaf was larger with more regular venation and the differentiation of venation was remarkable. The percentage of angiosperms was from 40%-60% in the flora, and eventually arose, becoming predominant, with important families well presented. This was probably from the Late Cretaceous to the Early Tertiary; (3) Herbs-Flourished stage: Some of woody plants were extinct, while herbs greatly increased, because of the changes in climate, sea level and mountain uplift during the Neogene period; (4)Quaternary stage: The mountain glacier in China, influenced by global glacial-interglacial alternation due to the climatic fluctuation, advanced and regressed during the Quaternary. The climatic fluctuation apparently affected the distribution of plants. But the components of the flora were similar to or slightly different from the features of the pres- ent one.      The aim of the present paper is to discuss the floristic regions at the second and third stages.      The Late Cretaceous-Early Tertiary stage:      A. The Late Cretaceous-Paleogene flora of northern China      1. Warm-temperate to subtropical deciduous broad-leaved and conifer forests in North and Northeastern China      2. Dry subtropical flora of Northwestern and Central China      B. Southern China Late Cretaceous-Paleogene flora      3. Deciduous and evergreen forests with coniferous elements in the subtropical coastal region of east China      4. Evergreen forests of South China      5. Evergreen forests of lower mountains in the Tethys      The Neogene stage-Herbs-flourished stage:      1. Temperate forests and grasslands to semidesert-desert floras of northwestern China;      2. Warm temperate deciduous forests of north and northeastern China;      3. Warm temperate to subtropical deciduous and evergreen forests of central and east China;      4. Evergreen forests of the subtropical and tropics mangrove vegetation of south China;     5. Subtropical evergreen and deciduous forests on the Yunnan and Xizang plateau.