Primary Systematics Of Paraprenanthes(Asteraceae—Cichorieae)

Paraprenanthes Chang ex Shih, belonging to Asteraceae of Cichorieae, is a new genus which was separated from Lactuca by Shi Zhu. There are some taxonomic problems that must be solved in Paraprenanthes, such as the fuzziness of the intergeneric boundaries between some related genera like Lactuca, leading to the uncertainty of its phylogenetic status in tribe Cichorieae and the vagueness of the boundaries of species because of the characters of different species are crossed and indistinguishable. In this paper, the extent and regularity of morphological variation between Paraprenanthes and its related genera are analyzed through studies of previous papers, analysis of specimens of herbariums and investigation in the wild. At the same time, we do researches on anatomy and micromorphology of achenes, analyze the chromosome karyotype of some species in this genus and all the acquired characters on the methods of cladistics synthetically. The results support the independent position of Paraprenanthes, make taxonomic revision of this genus and discuss the relationships between Paraprenanthes and its related genera.1. Analysis of morphological traitsThe analysis of morphological traits shows that characters of achenes are the major basis in distinguishing Paraprenanthes and the related genera, whereas they are not effective in the interspecific distinction. Currently, the shape of leaves is treated as major basis in the interspecific indentification of Paraprenanthes, and the main difference of some species is the shape of leaves. But the shape of leaves is unstable and is crossed between species, so it is unreliable to distinguish species according to the shape of leaves only. The numbers of inside involucre and florets is relevant, and leaf bases between species have stable variation, so they can be used in the interspecific classification. The strigillose type of the branches can be a complementary trait in the interspecific distinction. Some species have few specimens, making it different to analyze the morphological traits, so it is necessary to collect and analyze further.2. Anatomy research of achene wall The characters of anatomic achenes show that the anatomic structures of mature achenes of plants in Paraprenanthes are rib type, which consist of9-14well developed, relatively regular and homogeneous ribs, and a rib is usually made up of2-3layers of sclerotic fiber and4-8layers of libriform fiber, while there are only2-3layers of sclerotic fiber cells between ribs. The structures of fruit wall of achenes vary little in different species in the same genus, so it is difficult to distinguish them from anatomic structures clearly. But the results show that anatomic characters of achenes in different genera vary obviously, and this is valuable in the definition of relationships between different genera. Paraprenanthes is related with Notoseris, while it is remote from Pterocypsela, Lactuca and Prenanthes, and anatomic characters of achenes support the independent position of Paraprenanthes. The fact that Prenanthes yakoensis is different apparently from other species in Prenanthes and is related with Notoseris supports the classification of treatment that Prenanthes yakoensis was treated as Notoseris yakoensis in Notoseris by N. Killian.3. SEM observation of surface sculpturing of acheneThe researches indicate that the shape and arrangement of epidermal cells in the surface of achenes can be indexes in evaluating the intergeneric and interspecific relationship, because of the differences in different genera and species. Mainwhile, the consequences show that Paraprenanthes is related with Notoseris, while it is remote from Pterocypsela, Lactuca and Prenanthes, which support the independent status of Paraprenanthes. The researches of micro features of achenial surface support the treatment that Zhuang Xuan put P. sagittiformis in P. yunnanensis and N. Killian put P.pilipes in P. sororia, P. diversifolia, P. heptantha and P. sororia are related in the reason of the similarity of their micro feature of achene surface, while P. prenanthoides, P. glandulosissima, P. yunnanensis and P. polypodifolia is related and can be clustered. In the related genera, the evidence of micro features support that N. Killian put Pterocypsela elata in P. raddeana, Pterocypsela laciniata in P. indica and the combination of P. sonchus with P. formosana at some extent, and indicate that putting Pterocypsela in Lactuca by N. Killian is reasonable.4. Cytological study In this study, the chromosome numbers of Paraprenanthes and its related genera are all2n=18, which indicate the close relationships of Paraprenanthes and its related genera. In Paraprenanthes, the karyotype of Paraprenanthes diversifolia is2n=18=8m+10sm(2SAT), containing a pair of satellites, and it is reported firstly. Combining with others’studies before, Paraprenanthes diversifolia has same chromosome numbers with Paraprenanthes sororia, but they are different in karyotype, which supports the rationality of the species Paraprenanthes diversifolia grouped by N. Killian. We agree with predecessors that cytological features are related with achenial morphological characters, thus it is effective in the analysis of phylogenetic relationships in different genera. It is possible that the evolutionary status is between Notoseris and Pterocypsela(Lactuca), staying at the intermediate stage of the evolutionary process in this taxon.5. Analysis of cladisticsWe acquire a parsimony tree through the cladistic analysis of all the obtained morphological traits by software PAUP, which is made up of two clades, one of that is taxon having rib-type achenes such as Paraprenanthes, Notoseris and Prenanthes, the other is Pterocypsela (Lactuca) having swing-type achenes. Species in Paraprenanthes form an independent clade, having approval rate of61%bootstrap, which supports the independent status of this genus.6. Taxonomic revisionBased on the analyzing results above, the independent status of Paraprenanthes was supported, and the concept of this genus was redefined. A key to species of this genus was given. Four species are reduced to synonyms, the altogether7species are recognized. P. umbrosa is not completely understood and needs to be further studied. Each species is described and their distributions are mapped. And Flowering phenology, habitat, and interspecific relationships are also discussed.