Development of macrospore and microspore, male and female gametophytes of Fraxinus mandshurica Rupr. and its phylogenetic significance

The meiosis of megaspore and microspore mother cells and the developmental processes of male and female gametophytes in Fraxinus mandshurica Rupr.were observed by the paraffin sectioning method.Their embryological characteristics were revealed and its phylogenetic significance was discussed by comparison with the relative genera.The results indicate that F.mandshurica is a dioecious tree species;its anthers have 4 microsporangiates,and the development of anther wall is of dicotyledonous type and the tapetum belongs to glandular type.In the meiosis of microsporocyte,cytokinesis is simultaneous.Mature pollen grains are 2-celled.The ovary has 2 locules and there are 2 anatropous ovules in each locule.The ovule is unitegmic and tenuinucellatae.The meiosis of megaspore mother cell forms a linear tetrad,and the chalazal megaspore is the functional one.The development of embryo sac is of polygonum type.Flowers are protandrous.When pollen grains shed,female gametophytes have not matured yet and still in the meiosis stage of megasporocyte.The embroyological comparison suggests that the embryological characteristics of Oleaceae are more similar to Scrophulariales than to Gentianales.