The Identification of Araliaceae Species by ITS2 Genetic Barcoding and Pollen Morphology.

The genetic barcode ITS2 (ITS: internal transcribed spacer) and pollen morphology were used for the identification of the pharmacologically valuable wild Araliaceae species Panax ginseng, Oplopanax elatus, Aralia elata, Aralia continentalis, Eleutherococcus senticosus, and Eleutherococcus sessiliflorus inhabiting the natural forests of Primorye, Russia. The ITS2 locus successfully identified all six species, which supports the use of ITS2 as a standard barcode for medicinal plants. However, the ITS2 locus was insufficient for intra-specific discrimination in these species, neither within Primorye nor from other world representatives within GenBank. Araliaceae pollen was confirmed to undergo size-reducing metamorphosis. The final morphotypes were species-specific for each of the six species but could not discriminate intra-species geographic localities within Primorye. The morphologies of the final pollen morphotypes from homologous species inhabiting other parts of the world are not yet known. Therefore, whether pollen is applicable for Araliaceae intra-species discrimination between Primorye and other world localities could not be established. Based on these findings, we propose that the ITS2 genetic barcode and the final pollen morphotypes are suitable for the identification of Araliaceae species. However, further studies will be needed to determine the suitability of genetic and pollen traits for Araliaceae geographic authentication.

The pollen metamorphosis phenomenon in Panax ginseng, Aralia elata and Oplopanax elatus; an addition to discussion concerning the Panax affinity in Araliaceae.

To find more morphological characteristics useful for discussion on aralian or non-aralian Panax affinity, pollen morphological diversity was comparatively analysed in P. ginseng, Aralia elata and Oplopanax elatus collected during their pollination periods. In the anthers of both the buds and open flowers, the pollen average diameter varied between some species-specific maximum and minimal measurement. However, the larger pollen grains were typically found in the buds whereas the smaller pollen prevailed in the open flowers, testifying to the pollen size diminution during anther maturation. Based on this finding, the subsequent examination of pollen according to size decrease was put into operation as a method of pollen modification for the study. The structural mechanisms of pollen metamorphosis were identified as not being species specific but rather universal. These mechanisms are suggested to be the shrinkage of the pollen vegetative cytoplasm, the intine enlargement, the deepening of three colporate apertures provided by exine sunken into enlarged intine areas, the aperture accretion as well as the transformation of the exine from thick/sculptured into thin/less sculptured. During 'size-reducing metamorphosis', the pollen grains changed dramatically, going through a species-specific set of intermediate morphs to the final species-specific morphotype. In P. ginseng this morphotype is round (diameter is about 16 microm), in A. elata it is round with a single projection (diameter is about 15 microm) and in O. elatus it is ovoid with a single projection (average diameter is about 18 microm). In addition, every species is peculiar in having the unique vegetative cytoplasm inclusions and individual construction of the largest pollen exine. From a phylogenetic perspective, these findings presumably add support to the option of equal remoteness of P. ginseng from A. elata and O. elatus. The characteristics found seem to be suitable for examination of Panax affinity, by the subsequent study of more Araliaceae representatives.