Elymus duthiei(Melderis)G.Singh(Poaceae,Triticeae),a newly recorded species from China

Elymus duthiei(Melderis)G.Singh,newly recorded from Xizang,China,is described and illustrated in detail.Morphologically,the species is similar to E.anthosachnoides(Keng)Á.Löve ex B.R.Lu and E.glaberrimus(Keng&S.L.Chen)S.L.Chen but differs from the former in height and diameter of culms,number of nodes,width of leaf blades,and type of trichome and size of spikelets,and from the latter in distribution,height of culms,type of trichome of spikelets,and awn length.Detailed photo plates,descriptions,and distribution data are provided.

Quantitative Classification and Ordination of Plant Communities in the Upper and Middle Reaches of the Yarlung Zangbo River Basin

Based on vegetation survey data and environmental data of the Yarlung Zangbo River Basin, we conducted a quantitative ecological analysis of the vegetation community composition and the relationship between species and the environment in the study area. The results showed that 44 sampling sites and 68 plant species in the study area can be classified into seven subtypes: Artemisia minor + Stipa purpurea;Artemisia demissa + Stipa purpurea + Artemisia wellbyi;Kobresia pygmaea;Trikeraia hookeri;Sophora moorcroftiana + Cotoneaster multiflorus + Pennisetum centrasiaticum;Artemisia frigida;Potentilla fruticosa + Orinus thoroldii. Detrended correspondence analysis(DCA) indicated that both longitude and altitude play important roles in site and species distribution patterns. In addition, canonical correspondence analysis(CCA) revealed that in the upper and middle reaches of the Yarlung Zangbo River Basin, changes in temperature and precipitation caused by longitude are the main factors controlling the formation and transition of vegetation community types. Moreover, natural vegetation could be divided into three types: desert steppe community(source area), alpine steppe community(middle reaches region), and shrub community(confluence of Yarlung Zangbo River and Nyangqu River).