Molecular α-taxonomy of Hymenasplenium obliquissimum Complex (Aspleniaceae) Based on rbcL Sequence Comparisons(Systematic Biology)

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Hymenasplenium obliquissimum (Hayata) Nakaike is easily distinguished from other members of Hymenasplenium by its peculiar thin (two-cell thick) and translucent laminae with no air spaces, which are adapted to their subaquatic habitat. However, there also exist intermediate forms which are similar to H. obliquissimum in gross morphology but live in drier habitats, having thicker (3-4 cell layers) and opaque laminae with air spaces. The two different laminae forms sometimes grow together and create a complex in southwestern China and northern Thailand. In this work, we determined the rbcL sequences of 21 samples from the complex and conducted molecular phylogenetic analysis. Three major clades were detected ; one of them was composed only of specimens with thin forms from various localities, supporting the assertion that species with the thin laminae type (H. obliquissimum) are a different biological unit from those with the thicker laminae type. Two clades were recognized as having the thicker laminae type, but we failed to find any morphological difference between them. In the present study, we found sequence variations of the rbcL gene even in a fern species complex which is morphologically hard to distinguish. Such molecular techniques are useful even for monographic works which try to delimit species, especially of morphologically similar taxa like ferns.
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