| The Sect.Trachycercis Bunge belonged to Astraglus genus was considered to be represented with 77 species in the world,while 43 species that mainly distributed in arid and semiarid regins in the north and northwest of China.Plants of this section are acaulescent or caulescent,mostly caespitose,with bifurcate hairs,racemes subsessile.The majority of them lacked systematic study on population and morphology,which caused trouble in some species identification.Therefore,33 taxa of this section and A.koburensis were selected in this paper to study the micro-morphology of leaf epidermis and pollen by using stereo microscope and scanning electron microscope.Meanwhile,the evolutionary trend of extine ornamentation of pollen as well as ornamentation on the hair surface was analyzed.Geographical research was also studied to reveal theirs geographical distribution and morphological adaptation characteristics,which could provide some details for the classification and phylogeny of the group.The main outcomes were presented as follows:(1)All species had white bifurcate hairy with long pubescent and short pubescent.Only A.galactites had white hairs on the single side(back side),the other species are covered with hairs on both sides.There existed a marked difference in condition and quantity of hairs.The hair surface was smooth or striated,and the presence of papillae was common characteristic of all members of this group.The stomatal apparatus of 34 plants were amphistomatic and the stomata type was anomocytic.The shape of epidermal cells of most species was radiation,only a minority was polygonal.Anticlinal walls varied from straight-arched to sinuate.The cuticular layer was varied,but the ones of both sides of leaf epidermis were different in the same species.(2)Pollen grains are tri-zonocolporate,single,isopolar.There was no obvious difference in mesh size and convex in the mesh,while the pollen size was significant.The ratio of polar length and equatorial length was greater than 1.The shape of pollen grains were devided into three types,respectively: subprolate,prolate,prolate spheroidal in equatorial view.There were two kinds of pollen aperture that extended to the poles,one was narrow and the other was wide in middle and narrow in bipolar.The pore membrane was prominent or not prominent.Although the exine ornamentation existed difference among these species,it showed certain stability.The reticulate was the main type,whereas some had small perforations.The muri was smooth or wrinked.In polar view,the ornamentation of most species was nearly smooth and a few owed brain striated streak or reticulate,which could be applied as a better basis for classification.(3)Plants of Sect.Trachycercis were mainly composed of xerophytes that widely distributed in 15 provinces of China,among which Xinjiang possessed the most species.Compared with species,there was a wide distribution range and a significant vertical zone in A.scaberrismus and A.galactites.The main vertical zone was from 1000 to 2000 m.The effect of altitude was diverse for different species and the majority was unsuitable for growth at extremely low elevation(0-500 m).There existed geographical substitution and overlapping in species distribution.(4)According to the modern geographical distribution,distribution center and genetic relationship of 34 species in China,five different floristic geographical elements could be divided,including Northeast Asia-North China-Tangut element,Mongolian Plateau element,Mongolian Plateau-Junggar element,Pamirs-Tian Shan Mountain-Alxa element and Junggar Basin element.The species distributed in Xinkiang had closed relationship with the ones of Central Asia.In summary,the micromorphology of leaf epidermis as well as pollen could provide some evidence for the division of species and rule of systematic evolution.The geographical distribution revealed ability to adapt between the morphological characters of plants and habitats,which contributed to infer possible differentiation or migratory path. |
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