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The study of plant speciation on oceanic islands has improved enormously with the help of molecular systematics. Studies have targeted groups present on both the mainland and islands with the aim of understanding plant migration and evolution in isolation. In addition, relatively young volcanic islands give the opportunity to place the evolutionary process in a time frame, by dating molecular trees according to the age of the islands or by relying on the fossil record. Molecular phylogenetics can also be valuable in helping to reconstruct character evolution and understand the syndrome of characters diagnosing oceanic species.
Cordyceps sinensis, the caterpillar fungus in traditional Chinese medicine, has been intensively collected from nature in recent years. As a result, the establishment of the anamorph of this species has become important for large-scale culture to meet increasing demand for medicinal use and to ease exploitation of natural populations. To establish a reliable connection between the teleomorph and anamorph stages, the ITS nrDNA sequences were sequenced from both the stroma of the telemorph and cultures of the anamorph. Observations of microcyclic conidiation were also made on germinated ascospores and compared with the anamorph in culture. Hirsutella sinensis was confirmed as the anamorph of C. sinensis by both DNA sequences and microcyclic conidiation. Two recently described species, C. multiaxialis and C. nepalensis, were shown to share identical or almost identical ITS sequences with C. sinensis. These minor variations were considered to be within the range of variation exhibited within a species, but representing different populations. Sequences from other Cordyceps species included in this study exhibited considerable differences from each other. Therefore, these three entities are probably conspecific, and the names should be regarded as synonymous. The morphological characters used in the description of the two new species are discussed. It is suggested that ITS sequences provided useful information on establishing the anamorph–telemorph connection and assisting in the delimitation of species within Cordyceps.
Introduction
Plant systematics has experienced a methodological revolution in the last three decades. Parsimony analysis of character-state transformations and recognition of strictly monophyletic groups have given systematists the ability to explore the evolutionary relationships of plants with more rigour than in the past. Additionally, recent technological advances and developments in molecular biology have provided systematists with valuable new sources of data for phylogeny reconstruction. ‘Molecular systematics’ is a rapidly expanding field that includes the use of restriction endonuclease sites and nucleotide sequences, among other sources of information (Hillis & Moritz, 1990). Within the embryophytes and in some algal groups (e.g. Rhodophyta, Chlorophyta) chloroplast DNA is the molecule of choice for most plant systematists (Palmer et al., 1988). The chloroplast genome is small, highly conserved, present in a large number of copies and usually inherited only from the female parent. All green plants possess a chloroplast genome that is structurally conserved across most major groups. Thus the chloroplast genome provides a source of data potentially comparable at high taxonomic levels.
Other sources of molecular data are the mitochondrial genome (mtDNA; Palmer, 1992) and ribosomal RNA and DNA (rRNA and rDNA; Hamby & Zimmer, 1992). The mitochondrial genome in plants is large, and its nucleotide sequence evolves slowly. However, it is subject to frequent structural rearrangements and insertions and deletions. These attributes render plant mtDNA of little systematic use in studies involving either restriction sites, which are dependent on a relatively stable genome, or sequences (Palmer, 1992).
The genes for rDNA code for ribosomal rRNAs, and are very conserved owing to structural features.
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