Morphological Study On Floral Development Of Astragalus And Oxytropis

The morphological characteristics of flowers are always used to infer the evolutionary relationship.The ontogeny and development of floral organ may show the trace of evolutionary history.Therefore studies concerning flower ontogeny can reflect its taxonomic and evolutionary status.However there are very few studies on ontogeny of the genus Astragalus although China is a diversity distribution center of this genus.In this dissertation,four species of Astragalus and one species of Oxytropis were selected to make a comparison between these two genera using scanning electron microscope.This study tries to illustrate the relationships among species of Astragalus and that between Astragalus and Oxytropis based on floral organ ontogeny.This research provides a new idea for further study into the Astragalus.The detailed results were showed as follows:(1)The initiation of floral organ of the Astragalus is diversified,the most common way is unidirectional initiation,which appears from the abaxial side to the adaxial side.The overlapping of organs and appearance of common primordia can shorten the developing time and may be regarded as an evolutional character.These phenomena which also appear in other genera of Papilionoideae indicate that they have certain adaptability.Thus,the Astragalus may be evolved and specific in floral ontogeny.(2)The morphological characteristics of the floral organ development of the four Astragalus are similar in the early and middle stages.In the middle and late stages,there are some particular features such as rolled petals,adhering keels edge,diadelphous androecium.The semi-circular receptacular nectary is found in A.henryi.Based on the comparison of the inflorescence development between A.henryi and A.membranaceus,it was found that A.henryi formed one terminal inflorescence,finallyformed a raceme,while A.membranaceus formed many inflorescence terminal meristem several raceme,branched by racemes to form panicles.(3)The occurrence and development of O.ochrocephala was similar to the Astragalus.There was common primordia and organ overlap in the development process.The biggest difference was that the keel petals of O.ochrocephala formed a beak at the late development.