White Flower Spikes Are The Floral Organs And Embryonic Research

Speirantha gardenii (Hook.) Baill., the only species of the genus Speirantha Baker in the tribe Convallarieae (family Convallariaceae), is a perennial herb endemic to eastern China. It is often utilized as ornamental plant and medicinal herb, so the related studies have important economic significance and local interests. The present research aims to provide important information for the species conservation and new evidence on the phylogenetic relationships of the Convallarieae.The floral organogenesis and the embryological characters of S.gardenii were observed. The results are summarized as follows:1. Floral organogenesisThe floral organogenesis of Speirantha gardenii was observed for the first time under scanning electron microscope (SEM). Floral primordia initiated in a whorled and centripetal pattern:the two whorls of three tepals initiated firstly, then the two whorls of three stamens and one whorl of three carpels rose up. During the developmental process, the next whorls of primordia initiated opposite to the former whorls of primordia. The shape of the floral apex is irregularly triangular. A contour shape of the floral apex possibly sets the basic condition of the primordia number initiated in a whorl. The morphological features of tepal primordia are distinct from stamen ones, so no common primordia of tepals and stamens can be observed in this species. Anthers differentiated prior to the filaments formation. The three carpels fused into a syncarpous gynoecium at the early stage. The pattern of carpel is semiascidiate. The stigma surface became papillate. Upon the comparison with the Reineckia cornea (Andr.) Kunth in Convallarieae, this research indicated that S. gardenii differs from R. carnea in the floral developmental pattern:the tepal, stamen and carpel primordia of R.carnea initiated in a reversed unidirection type, but in S.gardenii as a whorled and centripetal pattern. The tepals, partly fused with filaments, formed a short tube at the late stage in R.carnea, but kept free in S.gardenii.2. Embryological studiesThe embryological characters of Speirantha gardenii were observed. The anther had 4 sporangiates and glandular tapetum. The mature anther walls comprised an epidermis, a layer of endothecium,2 middle layers and a single-layered tapetum. During the development of anther, the anther walls cells underwent a series of changes. Meiosis of the microspore mother cells was accompanied by successive cytokinesis, resulted in the formation of mostly isobilateral tetrads, occasionly linear, T-shape and decussate microspore tetrads could be observed. The mature pollen grains were 2-celled type. The ovary was trilocular with axile placentation, carrying anatropous, biteguminous and crassinucellate ovules. The micropyle was formed by the inner integument. The megaspore mother cell went through meiosis resulting in a T-shaped tetrad. The chalazal megaspore was functional. The development of embryo sacs conformed to the Polygonum-type. The embryogeny was Onagrad-type, and endosperm development as the Nuclear-type. The embryological characters of Speirantha gardenii was similar to other species in Convallariaceae.Based on the observation mentioned above and the available studies, such as data from palynology, morphological characters of leaf epidermis, karyotype as well as molecular biology, the analyses indicated:1. In Convallarieae, S. gardenii displayed many primitive embryological characters. So this species may be closer to the ancestral type of the convallarieae.2. Speirantha and Aspidistra were extremely similar in karyotype and embryological characters, indicating that they may share a common ancestor.3. The tribe Convallarieae is monophyletic, and the Aspidistreae should be reduced to the Convallarieae.