Studies On Systematics Of Genus Miscanthus (Poaceae)of China

Miscanthus is a kind of C4perennial grass, and belongs to Poaceae, tribe Andropogoneae, subtribe Saccharinae. It has recently attracted considerable attention as one of the most promising non-food bioenergy crop. According to the classification system in Flora of China, this genus comprises14species, most of which are distributed in eastern and south-eastern Asia and the Pacific islands and a few species extended to tropical Africa. There are seven species in China, including M. sinensis, M. floridulus, M. sacchariflorus, M. lutarioriparius, M. nepalensis, M. nudipes and M. paniculatus. However, the systematics of Miscanthus has long been disbuted. In this study, the analyses based on morphology, palynology and molecular systematics (SSR, ISSR, trnL-F, and rpl16) were employed together to clarify the phylogenetic relationships between those taxa within Miscanthus of China and then the taxonomic status of those controversial taxa to serve for the relevant genetic research and improvment and utilization of Miscanthus. The main results were as follows:1. MorphologyTwenty morphological characters plus chromosome numbers from36accessions of seven Miscanthus taxa were chosen for cladistic analysis. Based on the resulting data matrix of these characters, the MP phylogenetic analysis showed that the major groups corresponding to M. sinensis, M. floridulus, M. sacchariflorus and M. lutarioriparius were divided into two subgroups. The first subgroup (clade A) consisted of M. sinensis and M. floridulus and the second (clade B) was composed of M. sacchariflorus and M. lutarioriparius. M. floridulus became the secondary clade (clade C) of M. sinensis, and M. lutarioriparius becomed the secondary clade (clade D) of M. sacchariflorus. M. nepalensis, M. nudipes, and M. paniculatus grouped together to form a separated clade (clade E) which was distinctly excluded from the major group. The results supported the opinions that M. sacchariflorus and M. lutarioriparius should be combined into the genus Miscanthus and that M. nepalensis, M. nudipes and M. paniculatus should be excluded from this genus. Meanwhile, the results showed that the species status of M. floridulus and M. lutarioriparius were questionable.2. PalynologyThe palynology of39accessions from M. sinensis, M. floridulus, M. sacchariflorus, M. lutarioriparius, M. nepalensis, and M. nudipes were examined using light microscope and scanning electron microscope. The results revealed that pollen grain of Miscanthus was single with monoporate, and that the shape of pollen grain was subglobose. The pollen grain of M. nepalensis was small, but those of other taxa were medium in size. The exine sculpture of pollen grains of Miscanthus presented two types, granulate and verrucate. The latter could be divided into three subtypes: obscurely verrucate, verrucate and obviously verrucate. There were distinct difference in the exine ornamentation and pollen size between the group with granulate sculpturing containing M. nepalensis and M. nudipes and another group with verrucate sculpturing consisting of M. sinensis, M. floridulus, M. sacchariflorus, and M. lutarioriparius, so M. nepalensis and M. nudipes should be excluded from the genus Miscanthus and be recognized as a novel standalone genus, Diandranthus. M. sinensis, M. floridulus, M. sacchariflorus, and M. lutarioriparius shared high similarity in pollen morphology, which demonstrated the close affinity among them.3. Molecular systematicsThe phylogenetic analyses based on the data of SSR, ISSR, trnL-F and rpll6showed some similarity with the results from cladistic analysis. Namely, M. sinensis, M. floridulus, M. sacchariflorus and M. lutarioriparius constituted the main group in phylogenetic trees, and M. nepalensis, M. nudipes and M. paniculatus were clearly separated from the major group. But in the molecular phylogeny, the clade E was collapsed. M. nepalensis and M. nudipes formed a clade F, and M. paniculatus fell in an isolated clade. All of these three taxa were usually associated more closely with outgroup. Furthermore, the clade B was a monophyletic group and the clade D was collapsed. The results supported that M. sacchariflorus and M. lutarioriparius should be combined into the genus Miscanthus, that M. nepalensis and M. nudipes should be classified as a standalone genus Diandranthus, and M. paniculatus as a separate genus Rubimons. The combined phylogenical results based on morphology, palynology and molecular data suggested that M. lutarioriparius should be treated as a variety of M. sacchariflorus and M.floridulus as a subspecies of M. sinensis.