Systematic Study Of Two Enigmatic Taxa(Borthwickiaceae And Stixis) In Brassicales Based On The Anatomical Characters Of Stem

The two enigmatic taxas, Borthwickiaceae and Stixis,traditionally placed in Capparaceae, are embedded in the GRFT clade of the core Brassicales, and their systematic position and classification status has been kept controversial. The characters of stem often play important role in phylogeny studies. In order to clarify the systematic positions and classification status, the anatomical characters of both Borthwickiaceae and three species of Stixis were studied by using paraffin section and maceration method. The results are as follows:1.The exclusion of both Borthwickiaceae and Stixis from Capparaceae are supported. Because the two difficult groups and Capparaceae exist great differences, such as there is a continuous cambium in Borthwickiaceae stem, and Capparaceae most is not;Two difficult groups pith ray, which consists mainly of parenchyma cells without apparent starch grains, and Capparaceae in the pith ray tracheid, parenchyma cells contain a lot of starch grains;Did not see a single ray, two difficult groups and capers division has a large number of single ray.2.Support Borthwickiaceae and Stixis for core Brassicalesmembers of the GRFT branch. Based on Borthwickiaceae, Stixis,Forchhammeria and Gyrostemonaceae and Resedaceae on the morphological characteristics of similarities: cortex parenchyma cells are starch grains, xylem was wide and more columns of the rays,etc, all these support GRFT branch was established.3.This study found that Borthwickiaceae related taxa stems with great differences in anatomical structure, such as Borthwickiaceae cortex in corner collenchyma, whereas Stixis flake collenchyma; Borthwickiaceae xylem for complex pipe hole,and Resedaceae and Stixis besides complex pipe hole and single pipe hole; Borthwickiaceae not continuous cambium, pith and pith ray end no stone cells, while Stixis and Forchhammeria continuous cambium, pith and pith ray end have stone cells.4.Support the establishment of Stixaceae. As there is no continuous cambium Resedaceae in stem, pith ray tail and pith of stone cells. And, according to the results of our research has the obvious difference Stixis Resedaceae stem anatomical characteristics, its have continuous cambium in stem, pith and rays,end with a stone cells, etc., and these characteristics in the other groups such as Forchhammeria stem Stixideae also exist. Given Stixideae members form a lot, so this study supports the establishment of the Stixaceae.5.The stem anatomy can serve as a Stixis interspecies identification of important basis. Through the stem anatomical structure of Stixis three kind of observation, we find that there are some significant differences between three, such as Stixis suaveolens epidermis lignification degree is high, no table fur,catheter for the inside of a complex pipe hole and with rich contents,and Stixis ovata subsp. And Stixis scandens table fur, catheter for single pipehole, vessel elements inside without inclusions, these differences can be used as the important basis of species identification.