Floral Development In Nyssaceae

There is dispute that Camptotheca,Davida and Nyssa should be put into which families.They were put in the Nyssaceae or Cornaceae.Davidia sometimes was placed in Davidiaceae.Inflorescence and flower as the reporductive floral organs in angiosperm are valuable in plant systematics.Morphogenesis of inflorescence and flower is important because it contains abundant information of plant systematics.However,there are limited data of floral morphology and some are ambiguous.Moreover,floral developmental data in Nyssaceae are nearly abscent.Although the molecular systematics researches have presented the relationship amongst the nine families in Cornales,necessary supplemant of floral morphology in Nyssaceae is needed.We used Scaning Electron Microscope to research the morphogenesis of inflorescence and flower in Camptotheca and Davidia.Because of limited materials of Nyssa sinensis Oliv.,structure of mature flowers and morphogenesis of female flowers have been studied.Primiary results are as following:1.Camptotheca has botryoids composed of 5-7 capitate floral units(FUs)that are initiated acropetally.On each FU,flowers are grouped in dyads that are initiated fast and acropetally.All floral organs are initiated centripetally.Five calyx lobes are initiated in a helical(2/5 sequence)pattern.Five petals are initiated unidirectionally and in a valve aestivation.Ten stamens are in two whorls and appear in a quincuncial(2/5)sequence.Three carpels are initiated independently but the ovary is syncarpous and unilocular.The ovule is unitegmic and heterotropous.Style is cylindrical with three stigma lobes.Camptotheca has perfect flowers,but shows transition from hermaphroditic flowers to male flowers in an inflorescence.Flowers on the upper floral units(UFUs)often have robust styles and fully developed ovules;Flowers on the lower floral units(LFUs)have undeveloped styles and aborted ovules.Flowers on the middle floral units(MFUs)are transitional.2.There are two kinds of floral units in Davidia: homogeneous male floral units(HMFUs)and heterogeneous polygamous floral units(HPFUs).At an early stage,primordia of two kinds of floral units are smooth,naked and irregular semisphere-shaped.In HMFUs,secondary male floral units and male floral primordia are nearly simultaneously appear,while in a HPFU,a hermaphroditic flower primordium appears firstly,and then around which,secondary male flower primordia or male flower primordia appear.Finally,all male secondary floral units or flowers suddenly appear.Floral organs of hermaphroditic flower are initiated centripetally.Irregular crescent-shaped petal primordia appear at early stages and can be distinguished from stamen primordia with semisphere shape.Stamens on the hemaphroditic flowers approximately arranged in two whorls with development.Six to nine carpels are initiated independently and unite with the floral central regions to be axile placentation.Ovule is unitegmic,hemitropous and naked initially.Tepals of male flowers appear in the development.In a commen floral unit,stamens on the hermaphroditic flower and male flowers develop nearly synchronously.3.Nyssa sinensis Oliv.possesses male flowers,female flowers and female flowers with staminode.Male inflorescence is umbellate without bracts while famale inflorescence is cyme consisting of about four flowers with bracts.Number of floral organs in male flowers is unstable,and ususlly tetramerou,pentamerous or their variant.Sepals are unobvious at anthesis.Petals are triangular.Stamens are arranged in 2 whorls with ovate anthes and 3-colporate pollen.Female flowers are ususlly pentamerous.Crescent-shaped sepals appear in a quincuncial(2/5)sequence and develop slowly.Petals,semiellips-shaped,appear in a quincuncial(2/5)sequence and are imbrate aestivation.Staminodes are inserted in the inner whorl of the patels with obcordate anthers.There are 2(1)stigma lobes and 2(1)locule.The ovary is inferior with axile placentation and hemitropous ovules.4.The common feature of Camptotheca,Davidia and Nyssa are:(1)head floral units or head inflorescence;(2)complex sex breeding system and transform from hermaphroditic flowers to unisexual flowers;(3)hemitropous ovule with elongate bottom;(4)valvular dehiscence or longitudinal dehiscence resmble to valvular dehiscence.The common feature of the three genera,Diplopanax and Mastixia reflects on the arrangement of stamens and floral merism.Three kinds of floral units in Camptotheca,bared ovules in an early stage in Davidia and various inflorescences in Nyssa are their characters.The data from comparison of the inflorescence and flower development supports the results of the molecular systematics.