| Deyeuxia Clarion ex Beauv., a large genus within the family Poaceae comprising over 150 species, is distributed in the temperate region throughout the world and tropical mountains. This genus is morphologically highly polymorphous, and is one of the most difficult genera of Poaceae in taxonomy. This work is to revise the taxonomy of this genus from China based on evidence from gross-morphology, anatomy, ecology and phytogeography. The main results are summarized as follows:1. Gross-morphologyOn the basis of field observation and examination of herbarium specimens, the variation pattern of all the major gross-morphological characters in Deyeuxia was analyzed and their taxonomic significance was evaluated. The results showed that all of the characters are extremely variable, and the correlation of the characters is poor, thus leading to the scantiness of the reliable diagnostic characters in this genus. In general, the most reliable characters for the delimitation of species are the features of the glume surface (smooth, puberulent or scabrous), the relative length of callus hairs vs. lemma, the features of the lemma awn (presence or absence and its inserted position), the texture and epidermal structure of lemma. The secondly important characters are the degree of the denseness of basal branches of culm, the shape and the degree of compactness of panicle, the size of spikelet etc. Such characters as the hairiness of sheath, the length and shape of the ligule, the width of blade, the presence or absence of lashes on the margin of the glume are highly variable and are not considered to be of diagnostic value, for they can be easily modified by environmental condition or by some other factors. It must be noted that even the characters that are usually stable might also exhibit wide range of variation in some taxa, while those usually unstable characters seem to be of genetic stability in some cases and can be used as distinguishing features of taxa.2. Anatomy of both leaf and lemma epidermisLeaf epidermis of 67 samples representing 31 species and 3 varieties in Deyeuxia was observed under both light microscope (LM) and scanning electric microscope (SEM). The characters of adaxial leaf epidermis in Deyeuxia seem to be too complex to be of important significance for identification of species. Their abaxial epidermis is typically Festucoid, with long-cells, short-cells, silica-bodies, stomata, prickles, but without macro-hairs, micro-hairs and papillae. Some features, such as the sinuousdegree of walls of intercostal long-cell, the shape of silica-body, the distribution and frequency of prickles are often of specific diagnostic value.Lemma epidermis of all Deyeitxia species from China was also investigated under SEM. Great constancy of lemma epidermis was observed within the genus. Lemma epidermis of all the species studied is composed of long-cells and prickles, occasionally silica-bodies, but exhibits obvious differences in the characteristics of the walls of long-cells (thick or thin; markedly sinuous, sinuous or slightly sinuous) and the base of prickles (superficial or sunken). According to these features, the lemma epidermis of Deyeuxia species in China fell into 4 types. The first type is characterized by long-cells with thick and markedly sinuous walls and prickles with superficial base. This type is represented by 9 species, including D. arundinacea, D. scabrescens, D. lapponica, D. turczaninowii, D. kokonorica, D. neglecta, D. sichuanensis, D. conferta, D. moupinensis. The second type is characterized by long-cells with thick, slightly sinuous or sinuous walls and prickles with superficial base. This type is represented by 10 species and 1 variety, including D. effusiflora, D. sinelatior, D. nyingchiensis, D. tibetica, D. tibetica var. przevalskyi, D. anthoxanoides, D. himalaica, D. pulchella, D. rosea, D. holciformis, D. tianschanica. The third type is characterized by long-cells with thin, sinuous walls and prickles with sunken base. This type is represented by 4 species, including D. flav...
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