A Phylogenetic Study On The Genus Machilus Nees (Lauraceae)

The genus Machilus Nees (Lauraceae), with about 100 species, occurs mainly in tropical to subtropical Asia. China with 68 species distributed from southwest to south is a centre of diversity for the genus. Machilus is often characterised by its persistent (but not indurate) and strongly reflexed tepals in fruit. Based on the former systematic studies of Lauraceae, our research is trying to solve the systematic problems of the genus by means of the molecular phylogenetic and morphological analyses, and draw some preliminary conclusions for its phylogeny.After screening molecular markers from the noncoding cpDNA regions and low-copy gene Leafy, nrDNA ITS and cpDNA psbA-trnH sequences were used in the molecular phylogenetic analysis of Machilus. MP (Maximum Parsimony) and BI (Bayesian Inference) were employed to analyze the obtained data sets (ITS, psbA-trnH and psbA-trnH & ITS), the result of ITS Bayesian analysis was considered as the base to discuss the phylogeny of Machilus. Meanwhile,we checked through the morphological characters, which are usually used to separate Machilus from other genera of the Persea group.Based on the results of molecular phylogenetic analysis, we indicated that Machilus was monophyletic and had been set up as a distinct clade by itself in the Persea group, although this clade was closely related to the basal clade of Persea subg. Eriodaphne from Centre and South America. But it was more rather closely related to the Phoebe clade (including Phoebe, Dehaasia, Alseodaphne, Nothaphoebe and Persea subg. Persea) which mainly came from Asia. We also indicated that the persistent and spreading to reflexed tepals in fruit is to be a most important key character for resolving its generic delimitation against related genera (Phoebe or Persea) in Persea group. Meanwhile, molecular data hints that the species relationships within Machilus are much related to the adaptive variation of the inflorescence. In the cladogram of ITS sequence, Machilus minkweiensis is located on the base, but M.decursinervis and M.phoenicis are on the uppermost. The inflorescence of the former is inserted on the lower part of young branchlet, very elongate, long-pedunculate and few branched, without bracts at the base when in anthesis, but the inflorescences of the latter two are inserted near the top of branchlets, short-pedunculate and many-branch, with persistent bract at the base when in anthesis. So we think there is an adaptive variation for the cold climate in the phylogeny of Machilus, and we also think the former is a primitive one but the latter is an advanced one.However, the infragenenic phylogeny of Machilus are poorly resolved now, we suggested that more smaplings from Machilus and more powerful molecular markers are needed in the future study.