中生代银杏类植物系统发育、分类和演化趋向

Mesozoic Ginkgoaleans:Phylogeny,Classification and Evolutionary Trends

长期以来银杏类植物化石分类都依据营养叶形态为基础。由于叶形态的多型性和异源性 ,导致分类和系统发育解释的紊乱。根据对保存完好的繁殖器官 (胚珠器官 )系统发育分析结果所作的银杏目分类表明中生代除了银杏和银杏科以外 ,至少还存在着 3～ 5个已灭绝的科级单元。此方案把已知其繁殖器官的成员和仅仅根据营养器官建立起来的分类位置不明的属严格地区分开来 ,并注明各科的限定性特征和已知成员的地质地理分布。银杏目植物自古生代起源 ,至早中生代以后朝着不同的方向辐射 ,呈现出丰富的多样性并经历了错综复杂的演化过程 ,其总的演化趋向是退缩 :叶片扁化、蹼化和融合 ;胚珠器官简化 ,胚珠增大、数目减少 ,珠柄趋于消失。

In this article,the recent progress made in studies of Mesozoic ginkgoaleans,especially those of the Chinese material,is summarized with a brief review of the origin and distribution of ginkgoaleans in the geological history.For a long time,our knowledge of ginkgoaleans has been obtained mainly from fossil leaves that are of little taxonomic and phylogenetic significance.The proposed classification was based on phylogenetic analyses of well-preserved taxa of which not only vegetative organs,but ovulate organs were known.It is supplemented here with the defining features,and geological and geographical distribution of the extinct families.The taxonomic positions of taxa for vegetative organs are left undetermined unless they are found related to reproductive organs.The general evolutionary trends of ginkgoaleans since Permian was reduction of both vegetative and reproductive organs in spite of being greatly diversified in morphology in the Jurassic and Early Cretaceous time.