Comparative study of floral developments and its systematic importance in the genus Astragalus L. and Oxytropis DC. (Fabaceae, Leguminosae: Papilionoideae)

Abstract

The initiation pattern of the floral organs of the Astragalus species displays uniqueness at the initial stages of ontogeny. However, its most common way is unidirectional initiation, which occurs from the abaxial to the adaxial sides. The overlapping of organs and the emergence of common primordia shortens the time of development and is of an evolutionary advantage to the genus. Astragalus species are constantly evolving, and they are bestowed with unique floral ontogeny that offers various advantages to these plants to survive and adapt to changing environmental conditions. The morphological features of the floral organ production of four Astragalus species were identical in the early and middle stages of development. During the middle and the late stages, some unique features such as rolled petals, sticky keel tips, diadelphous androecium were observed. Semi-circular receptacular nectaries were found in Astragalus henryi. Comparison of the inflorescence development between A. henryi and A. membranaceus revealed that A. membranaceus formed one terminal inflorescence, which developed into a raceme while A. henryi formed a variety of terminal inflorescences, branched by racemes to form panicles. Development of common primordia and organ overlap was also observed in both Oxytropis ochrocephala and Astragalus species. However, the most significant difference was observed in the keel petals of O. ochrocephala, which developed a beak at the later stages of development. The study unravels interesting relationships between four species of Astragalus and one species of Oxytropis. Study of floral ontogeny through series of sections using various microscopic techniques provided insights into the understudied floral traits of the genera. Such studies also need to be corroborated with other empirical evidence and analyses.