The Embryology Of Borthwickiaceae

Borthwickia trifoliata is a member of the GRFT clade of core Brassicales. Traditionally, it has been placed in Capparaceae. But the systematic positions and allies remain controversial.Embryological characters are potentially of systematic significance. In the present study, embryological characters of Borthwickiaceae were observed.Main results as follows:1. The embryological features of Borthwickiaceae. Stamens numerous, filaments slender, anthers dorsifixed. Carpel(4-)6, locule(4-)6, axial placenta, ovule anatropous, longitudinal lined up per locule. Seed kidney-shaped, endosperm absent, with two curved cotyledons. Ovule with thick nucellus and double bead, micropyle is zig-zag. Nucellus have a archesporial cell, linear tetrad. The development type of female gametophyte is Polygonum-type with seven-celled and eight-nucleate at maturity. Each stamen has four microsporangias in two thecae. The development type of the anther wall belongs to the dicotyledonous type, the tapetum is glandular,The microspore tetrads is tetrahedral. A microspore mother cell is accpmpanied by simultaneous cytokinesis. Pollen grains are2-celled.2. Borthwickia trifoliata should be removed from Capparaceae.By comparing the embryological features between Borthwickia and Capparaceae, many differences between them were found: the growth from of the ovule, nucellus spore cell number, the shape of the bead hole, and tetrad shapes. Therefore, Borthwickia should be removed from Capparaceae based on our results.3.Borthwickia trifoliata embed in the clade GRFT of core Brassicales. By comparing the embryological features between Borthwickia and Capparaceae, many similarrities could be found,the tapetum is glandular, pollen grains are 2-celled, the development type of female gametophyte is polygonum-type,the pollen grains are tricolporate. So our results support Borthwickia is a member of the GRFT clade.4.The present study provide new evidences for Borthwickia should be treated as a separate family. Embryological features among Borthwickiaceae, Resedaceae and Borthwickia shown that the development type of anther wall belongs to the dicotyledonous type, two middle layers, Ovule growth form, nucellus is always one-celled, inner and outer integument is two layers thick. The charaters are different from the sister clade of Resedaceae and Gyrostemonaceae. In the newly published APG IV, Borthwickia trifoliate was placed in Gyrostemonaceae, our results don't agree this opinion,but support Borthwickia trifoliata as a separate family.To sum up, the present study do not only investigated the first comprehensive embryological features of Borthwickia, but also provide new evidence for Borthwickia should be treated as a separate family.