Phylogenetic Relationship And Biogeography Of Thoreales Based On Gene Sequences

Thoreales is an order of freshwater red algae including thirteen taxa. They can only live in cool, clean and flowing fresh water. In recent years, a number of springs and streams have been seriously polluted by substantial development of tourism resources. So the growth of Thoreales has been suffering a serious threat and some species were on the verge of extinction. Thus, the researches on phylogenetic analysis, ecological distribution and biogeography for the protection of this group are very important and significant.Thoreales is belonging to Rhodophyta, Rhodophyceae, Floridophaceae and has a short history. Its thallus (gametophyte) is multiaxial, the pit plugs contain two cap layers and the outer one is plate-like. Two genera, Thorea Bory (11 species) and Nemalionopsis Skuja (2 species) were reported in the world at present.Thorea hispida is the type species of genus Thorea and distributed widely. Five genes, rbcL,18S rRNA, psaA, psbA and COI, were amplified and sequenced for samples of Thorea hispida collected from Shanxi and blasted with other groups, then the phylogenetic trees were constructed. Combined with the morphological and biogeographical characteristics, the results showed that the members of Thoreales were aggregated in one branch, separated from other groups. So the result supported that Thoreales was an independent order. There was not a close genetic relationship between Thoreales and Batrachospermales with a higher statistical support. But this result was still imperfect and more researches have to carry out. In addition, it was presumed that Thoreales originated from the Eurasian continent based on its modern geographical distribution and molecular data. The phylogeny analysis showed Audouinella, Thorea and Batrachospermum are relatively independent. This provides a considerable basis for dealing with the relationship among Audouinella, Thorea and Batrachospermum. Meanwhile, these data also provided scientific informations for the phylogenetic analysis of subclass Floridophaceae.