| The classification of the Cladophorales has been a matter of much confusionbecause of few morphological characters and extensive morphological plasticity. Inorder to clarify the delimiting criteria and phylogenetic systematics on the order,morphology observation and molecular analysis have been conducted on the seriescollection of Cladophorales species along the coasts of China sea. In addition, the lifehistory of Cladophora gracilis has been studied.With morphology observation to the 31 samples, 16 species have been identified:Chaetomorpha aerea (Dillwyn) Kuetzing, Ch. brachygona Harvey, Ch. liaodongensisLuan et Ding, Ch. linum(Müller) Kuetzing, Ch. valida (Hooker et Harvey) Kuetzing,Cladophora albida (Nees)Kuetzing, Cl. catenata*, Cl. expansa (Mertens) Kuetzing,Cl. fascicularis (Mertens ex C.Agardh) Kuetzing, Cl. gracilis (Griffiths) Kuetzing, Cl.hutchinsioides van den Hoek et Womersley, Cl. laetevirens (Dillwyn) Kuetzing, Cl.opaca Sakai, Cl. stimpsonii Harvey, Rhizoclonium implexum (Dillwyn) Kuetzing, R.riparium (Roth) Kuetzing ex Harvey, with five unkown species. Several characters usedas classification criteria have been summarized and appraised. Branching style and density, cellshape, thallus color and texture can vary with environmental condition and age of plants evenwithin the same species. Relatively, cell size and the ratio of length and width can be very usefulclassification characters. Highly divergent ITS and relatively conserved 18S rDNA sequences are used to additionalclassification. After DNA extraction, primers designing, PCR extending and sequencing,phylogenetic trees were constructed. Results showed that both the sequences could be used asmolecular markers to distinguish confused species. Following the approach, on combination ofmorphological taxonomy and molecular analysis, 14 species and 1 variety were identified asfollows: Chaetomorpha aerea (Dillwyn) Kuetzing, Ch. brachygona Harvey, Ch.liaodongensis Luan et Ding, Ch. linum (Müller) Kuetzing, Ch. valida (Hooker etHarvey) Kuetzing, Cladophora albida (Nees) Kuetzing, Cl. expansa (Mertens)Kuetzing, Cl. fascicularis (Mertens ex C. Agardh) Kuetzing, Cl. gracilis (Griffiths)Kuetzing, Cl. hutchinsioides van den Hoek et Womersley, Cl. laetevirens (Dillwyn)Kuetzing, Cl. opaca Sakai, Cl. stimpsonii Harvey, Rhizoclonium riparium (Roth)Kuetzing ex Harvey and R. riparium var. implexum (Dillwyn) Rosenvinge. Additionally,the relationships between several questioned species were clarified: a. Ch. aerea was far related toCh. linum on the phylogenetic tree and they were distinct species; b. R. riparium and R. implexumhad virtually identical sequences and R. implexum should be attributed to the variety of R.riparium; c. Cl. fascicularis and Cl. expansa were distinct from Cl. vagabunda.Both ITS and 18S rDNA sequences exhibited appropriate divergence among the species oforder Cladophorales on the phylogenetic tree. Sequence analysis showed that interspecificdivergence was larger than that of intraspecific. That is, for 18S rDNA, divergence is0.0%~0.1% within species, 0.3%~6.1% among species, and for ITS, it is 0.0%~1.7%within species, 4.9%~63.4% among species. They are potentially powerful tool for assistantidentification and can be used as DNA barcoding of order Cladophorales.The phylogenetic trees constructed with ITS and 18S rDNA both demonstrated that the threegenera were not monophyletic as well. The known taxonomy hierarchy of the three generacould not reflect the evolution events and should be reconsidered. We proposed thatthe three genera merged into the earliest built genus Rhizoclonium Kützing.As the crucial aspect of current taxonomy, experimental taxonomy was alsoconducted in present study. Plants of Cl. gracilis were cultured and the growth processwas observed. The species has a typical Cladophora-type life cycle, which consists ofan alternation with diploid sporophytes and morphologically similar haploid gametophytes. Parthenogenesis also occurred.Besides, as parts of research project of green bloom on Enteromorpha prolifera,the morphology distinction between E. prolifera and E. clathrata was compared indetails. And ITS sequence was analyzed to confirm the genetic difference between thetwo species. |
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