Systematic Studies Of The Muhlenbergia (Poaceae)

The Muhlenbergia Schreber belongs to the Chloridoideae (Eragrostoideae), about 155 species, distributes in North America, Himalayas to Japan, the main habitat is in North America; 6 species distribute all over of China. Its systematic position in the Eragrostoideae has been disputed for long time.Micromorphological study on leaf nether epidermis of 40 species of Poaceae (representing 27 genera) shows that the epidermal structure include long cell, short cell, subsidiary cell, micro-hairs, macro-hairs, prickle-hairs and papillae et al. The appearance and distribution of them is inconsistent. We divided the taxa into four types and 5 subtypes. Contrasted with the classification system of Poaceae, typeâ… are equals with the subfam. Eragrostideae; typeâ…¡includes the taxa of subfam. Pooideae; typeâ…¢equals to the subfam. Panicoideae; and Type IV represent the subfam. Oryzoideae. This conclusion was consistent with the studies on combinative patterns and shape diversity of leaf epidermal constituent cells. We also divided the typeâ… into five subtypes, corresponding to the Eragrostideae,Chlorideae,Zoysideae,Sporoboleae independently; Muhlenbergia belongs to the subtype 5, different with Sporobolus and Crypsis (belongs to subtype 4), who has close relationship with Muhlenbergia. The incorporation of Muhlenbergia , Sporobolus and Crypsis is unadvisable.Caryopsis morphology. Light anatomical microscopes are used to examine caryopsis features of 41 species (representing 33 genera) of Poaceae. Three caryopsis types and four subtypes can be recognized according to differences in types of fruits, Solid figure ,ventral face and hilum morphology et al. These types and subtypes were equal to the four subfamilies (Eragrostideae, Pooideae, Panicoideae, Oryzoideae) of Poaceae. Based on the solid figure, we also divided the subtype 1 into 4 groups, corresponding to the Eragrostideae,Chlorideae,Sporoboleae independently; The caryopsis of Muhlenbergia has three prism shape, no compression, embryo ratio 1/2, which different with Sporobolus and Crypsis (belongs to group 3). All of these show that Muhlenbergia has its peculiar status in the Eragrostoideae.Molecular phylogeny. Using the nuclear internal transcribed spacer (ITS) DNA fragment, we established the phylogenetic tree of Poaceae. The results show that Poaceae formed three large clades, corresponding to subfamily Pooideae, Eragrostideae and Panicoideae. Within Clade Eragrostoideae there are 7 sister clades, Muhlenbergia belongs to clade iii, independent from Sporobolus and Crypsis. Consistent with the results of chloroplast DNA matK sequence and restriction sites of plastid DNAs, and also support the conclusion Micromorphological study on leaf nether epidermis and Caryopsis morphology. In conclusion, based on Micromorphological study on leaf nether epidermis, Caryopsis morphology and Molecular phylogeny, the present study indicate that the genus Muhlenbergia should be the tribe rank, establish the tribe Muhlenbergiieae.The rults show that the Bouteloua and Buchloe didn't close with the Chlorideae, we proposed to promoted the two genera to tribe Boutelouneae.The Eragrostis established an independent clade (clade vii), which far from the taxa of clade ii, indicate that the Eragrostideae is not monophyletic group. The systematic position of genera in Eragrostideae needed to be reconstructed.The evidences from micromorphological characters of epidermal structure and ITS phylogenetic tree indicated that the Leptochloa had close relationship with the Chlorideae, systematic studies needed to be done in the future.