Systematic Of Genus Lactuca And Related Genera In China

The genus Lactuca and related genera is classified in the tribe Lactuceae, family Compositae/Asteraceae. Although the tribe Lactuceae(=Cichorieae) itself is well defined by its ligulate florets and copious milky latex, the delimitations and phylogenetic relationships among its genera and species are still disputed. The numerous, often contradictory classifications for "Lactuca-Prenanthes" complex which is consist of Lactuca L. and related genera illustrate this dispute. In China, the classification of Lactuca L. and related genera was base on Shih's classification. Shih revised the genera Lactuca, Prenanthes etc.,divided from which and established five new genera. Because Shih's classification was mainly based on specimens and morphologic characters, especially on achenes',more evidences need to be provided to evaluate Shih's classification. Base on the summary of the previous taxonomic work of Lactuca L. and related genera, the aim of the present study is to(1)make more experimental evidences base on macromorphology, molecular study, leaf anatomy; (2) primary clarify the relationship and delimination between Lactuca L. and related genera in China and the relationship of some species under these genera.Phylogenetic analyses of 12 representative species from the 5 genera of Lactuca L.and related genera were performed using three chloroplast sequences and combined data. The sequences have been submitted to Genbank with number GU109286-GU109333.The trnL-F intergenic spacer & trnL intron,psbA-trnH intergenic spacer and trnK/matK gene contain several insertions and deletions (indels) in Lactuca L. and related genera with the length of 800-849bp and 416-455bp,2736-2790bp.The strict consensus trees were established use the method of maximum parsimony. This molecular study indicated that(1)Shih's separation of genus Lactuca, Mulgedium, Ptertocypsela, Chaetoseris and Paraprenanthes is reasonable base on molecular study; (2) There is some difference of the molecular sequence of L. sativa and L. serriola. Whether they are conspecies need other evidences.(3) Because Lactuca dolicophylla has a closer relationship to Mulgedium other than L. sativa and L.serriola.,L. dolicophylla Kitam may be a transition species between Lactuca and Mulgedium (4) Lactuca perennis which is belong to Lactuca sect. Lactuca subs.cyanicae has a closer phylogenetic relationship to the type species of Lactuca s. s. than to Pterocypsela indica. The molecular study didn't support the delimination of Lactuca sect. Lactuca subs.Cyanicae from Lactuca s.l.;(5) Ch.lyriformis has the same molecular sequences of Ch. cynaea.The molecular study supported the combination of this two species.(6) There is a closely relationship between Pterocypsela indica and Pt. laciniata in molecular sequence. The result support Pt. laciniata being a varition of Pt. indica.Leaf anatomy study based on 12 species,16 samples of Lactuca L. and related genera was conducted. The result indicated that leaf cross-section structure character can provide little taxonomic information, because nearly all the characters are quantitative traits and of high consistency among different species. It is difficult to conclude special characters belong to different genera.Lactuca L. and related genera from China was systematically arranged based on observation of a large number of specimens, investigation of field populations and experiments. Base on macro-and micro-characteristics, the relationships between Lactuca L. and related genera in China were discussed. The molecular study indicated that the relationships among genera Lactuca, Mulgedium, Ptertocypsela and Chaetoseris were closely. Notoseris and Prenanthes had a distant relationship from them. The taxnomic position of Paraprenanthes is between these above two groups. The achene rostrum in Lactuca, Mulgedium, Ptertocypsela, Chaetoseris is distinct, while in Notoseris and Prenanthes is not exist. The achene top of Paraprenanthes is rostrate-like. The achene anatomy of Lactuca, Mulgedium, Ptertocypsela, Chaetoseris is winged-type, while in Notoseris, Prenanthes and Paraprenanthes is ribbed-type. All these are correspond to molecular evidence. Finally, key of Lactuca and relatated genera was made.