Developmental Morphology Of The Petal (Nectar) Of 5 Genera Of The Family Medispermaceae

Flowers of the angiosperm are highly specialized reproductive organs, which are adaptive to pollination. Petals are derived from other parts of the flower. Petal of core Ranunculales is called nectary leaves, and its origin and evolution has been studied by many systematic and evolutionary botanists. The nectary structure, developmental characteristics of nectary leaves are of great significance for further exploring the origin and evolution of petals.Menispermaceae is one of the core Ranunculales. Flower is unisexual. In Menispermaceae, petals(nectary leaves) are usually green, short and has two lobes at the top. In this study,5 species of 5 genera (2 tribes) in Menispermaceae were investigated, the petal structure, developmental features and nectary structure were described. The main results are as follows:(1) The shape of mature petals(nectary leaves) shows diversity:broadlyoval balde,with a claw at the base, an inner fold at the top edge (such as Tinospora sagittata (Oliv.) Gagnep.); with a claw at the base, kidney shaped like a heart (such as Menispermum dauricum DC); deep two-lobed obcordate and two inner folds at the base (such as Cocculus orbiculatus DC.); shell-shaped, the top two-lobed or entire, with two protuberances on both sides of the central (such as Stephania dielsiana Y.C. Wu); columnar or both sides reverse fold abaxially, the corolla is combined to form a disc or a cup (such as Cyclea racemosa Oliv.).(2) The petals(nectary leaves) are composed of epidermal cells, parenchyma tissue and vascular bundle. There are 10 epidermal cells according to cell shape, respectively as type 1:cylindrical cells, with sporadic secretion on the cell surface; type 2:the cell shape is nearly circular, with strong secretion on the surface; type 3:cell shape is polygon, with longitudinal striations and sporadic secretion on the surface; type 4:cell shape is rectangular, neatly arranged, with strong secretion on the surface; type 5: cylindrical cells, with no secretions on the rough surface; type 6:papillary cells with protuberance in the center, the cells showed equal diameter polygon, no secretions; type 7:papillary cells with protuberance in the center, cells were oval with no secretions on the rough surface; type 8:polygonal cells, with transverse striations and no secretions on the surface:type 9:short rectangular cells, with transverse striation s and no secretions on the surface, arranged neatly; type 10:long rectangular cells, with transverse striations and no secretions on the surface, arranged neatly.4 types of secretory epidermal cells can be recognized:cylindrical (such as T. sagittata), suborbicular (such as Cyclea racemosa), polygon (such as M. dauricum. Cocculus orbiculatus) and rectangle (such as Cocculus orbiculatus). Cocculus orbiculatus and T. sagittata have the most complex type,4 kinds of epidermal cells. The epidermis consists of one layer of cells, and there is usually no cuticle on petal epidermis (except Cocculus orbiculatus). There are 5-15 layers of parenchyma cells, which arranged loosely, stained lighter,1 vascular bundle (except Cyclea racemosa, which has no vascular bundle).(3) The developmental characteristics of petals(nectary leaves) in early developmental stages were similar in the family. After the initiation of the long-oval shaped petal primordia, gradually developed into oval-shaped, then egg-shaped. To the later stage of development, two lobes at the top, and convolution or protuberance at the different positions of petals cause the division.1.one infolding at the top raised adaxially, lobes are absent(such as T. sagittata); 2.two infoldings are raised adaxially at the base, lobes are absent at the top(such as M. dauricum); 3.two infoldings are raised adaxially at the base, two lobes are at the top (such as Cocculus orbiculatus); 4.two protuberances are raised adaxially on both sides of the central, two lobes are at the top or absent (such as S. dielsiana); 5. lobes are absent at the top, two reflexions are raised abaxially at the base or absent, detached or accrete (such as Cyclea racemosa).(4) The nectariferous tissue is differentiated at the later developmental stage of petals(nectary leaves), when convolutions or protuberance raised on the petal. Nectariferou tissue is usually located at the convolutions (such as T. sagittata?M. dauricum?Cocculus orbiculatus)?protuberance (such as S. dielsiana)?blade part (such as Cocculus orbiculatus?Cyclea racemosa)?or lobes of petal (such as Cocculus orbiculatus). The nectary is composed of secretory epidermis and 2-3 layers of parenchyma cells under it or secretory epidermis only. The secretory cells are small in size, tightly arranged, with dense cytoplasm and large nucleus.According to the early developmental features of petal (nectary leaves) in Menispermaceae, petal primordium is long-oval shaped, stamen primordium is hemispherical, short interval period between the petal and stamen, and retarded development,1 vascular bundles in the base. This study provides the basis for the further study on the origin and evolution of petals in Ranunculales.