Flower Development And Its Systematic Significance Of Two Curious Groups In The GRFT Of The Core Brassicales Borthwickiaceae And Stixis

The “GRFT” clade is an important clade of the core Brassicales,which including Forchhammeria,Tirania and Stixis,Resedaceae,Gyrostemonaceae,and Borthwickiaceae.The taxonomic status of Borthwickiaceae and Stixis is controversial.In order to resolve this issue,we studied flower development in these two groups by scanning electron microscopy.summarizes as follows:(1)It is supported that Borthwickiaceae and Stixis are segregated from Capparaceae.By observating the flower development,we found obvious difference between Capparaceae and these two groups.Capparaceae has 4 speals,4 petals,and polymerous androecium.Its centrifugal stamen primordium is in 4-5 whorls,and each whorl is 12-14;Borthwickiaceae has 6 symsepalous calyx,6 petals,and syncarpous pistil 4-5 fused carpels.Its stamen primordium has 3 centripetal whorls,each whorl is 19-23;Stixis has 6 sepals,no petal,and tricarpic gynecium.Its centrifugal stamen primordium has about 7-8 whorls,each whorl is3.Thus,It is supported that Borthwickiaceae and Stixis are segregated from Capparaceae(2)It is supported that Borthwickiaceae is a monotypic family.Although the Borthwickiaceae is sister to Resedaceae and Stixis,there are many differences in their flower development.Borthwickiaceae has centripetally ring-shaped stamen primordium and 4 or 5united carpels.Resedaceae has centrifugally bunched or annular stamen primordium and syncarpous pistil.Stixis has centrifugally spherical stamen primordium and 3 united carpels.It suggests that Borthwickia should not be placed in the Resedaceae.but in a monotypic family.(3)The taxonomic status of stixeae remains uncertain.The flower development of Stixis differes form the Resedaceae.Stixis is actinomorphic flower,no petals and nectary,spherical stamen primordium,syncarpous pistil with three carpels;Resedaceae has petals,disclike nectary,fascicled or ring androecia primordium,and polymerous androecium.Although there are many differences between Stixis and Resedaceae,but lack of data about other members of stixeae makes the taxonomic status of stixeae remains uncertain.