Morphological Study On Floral Development Of Five Species In Leguminosae

Flowers are the reproductive organs of angiosperms, and they play a crucial role in the diversity of angiosperms. The origin and evolution issues of flowers have always been a hotspot for the systematic and evolutionary botanists. There is much more important evolutionary information during floral devlopment comparing with the mature structures. The floral development of 5 species from 5 genera, 3 subfamilies in Leguminosae are studied using scanning electron microscopy(SEM). The results are listed as follow:(1) The floral organ initiation of Albizia julibrissin was common in tribe Ingeae(Subfamily Mimosoideae) including the helical initiation of sepals, the simutaneous initiation of petals and the ring meristem in the position of stamens. As for Caesalpinia decapetala(subfamily Caesalpinioideae, tribe Caesalpinieae), all of its organ whorls were initiated unidirectional from the abaxial sides to the adaxial sides, similar to the most highly derived subfamily, Papilionoideae. However, from the aspect of floral development, it lacked specialization of petals and fused staminal tube, distinguished from papilinous flowers.Common primordia was initiated in Astragalus taiyuanensis and Hedysarum multijugum,which shortened time intervals between the initiations of different floral organs. Such characters were considered to be evolved.(2) The mature gynoecium were diverse in morphology. Crateriform stigma was found in Albizia julibrissin and Caesalpinia decapetala, while the papillate stigma appeared in the three Papilionoideae species: Caragana rosea, Astragalus taiyuanensis and Hedysarum multijugum, which had hooked style(medium length), in contrast, the style was erect in Albizia julibrissin(long) and Caesalpinia decapetala(short). Gynophore in Hedysarum multijugum was much longer than the other species in present study. Ovary was densely haired in Caesalpinia decapetala and Astragalus taiyuanensis.(3) All of ovules of the five species studied here had two integuments. The inner integument initiated before the outer integument, but the outer integument would grow faster and cover the inner integument to form the exostomial micropyle. The ovules were initiated before the carpel appressed in Caesalpinia decapetala, which was rarely happened in Leguminosae and angiosperms. All the species initiated ovule primordia in two rows but donot have the same ovule numbers. 21 ovules were found in Astragalus taiyuanensis and only3 ovules were found in Hedysarum multijugum.(4) Common primordia was found both in Astragalus taiyuanensis and Hedysarum multijugum but not in Caragana rosea. It provided evidence to the opinion that Caragana rosea was not belong to Galegeae or Hedysareae, but to Caraganeae, a newly resurrected tribe.