It has been suggested that rbcL and matK are the core barcodes in plants, but they are not powerful enough to distinguish between closely related plant groups. Additional barcodes need to be evaluated to improve the level of discrimination between plant species. Because of their well-studied taxonomy and extreme diversity, we used Chinese Lysimachia (Myrsinaceae) species to test the performance of core barcodes (rbcL and matK) and two additional candidate barcodes (trnH-psbA and the nuclear ribosomal ITS); 97 accessions from four subgenus representing 34 putative Lysimachia species were included in this study. And many closely related species pairs in subgen. Lysimachia were covered to detect their discriminatory power. The inefficiency of rbcL and matK alone or combined in closely related plant groups was validated in this study. TrnH-psbA combined with rbcL + matK did not yet perform well in Lysimachia groups. In contrast, ITS, alone or combined with rbcL and/or matK, revealed high resolving ability in Lysimachia. We support ITS as a supplementary barcode on the basis of core barcode rbcL and matK. Besides, this study also illustrates several mistakes or underlying evolutionary events in Lysimachia detected by DNA barcoding.

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The genus Primula is extremely diverse in the east Himalaya-Hengduan Mountains (HHM) in China as a result of rapid radiation. In order to overcome the difficulty of morphological classification of this genus, we surveyed three plastid regions (rbcL, matK, and trnH-psbA) and two nuclear markers (ITS and ITS2) from 227 accessions representing 66 Primula species across 18 sections, to assess their discriminatory power as barcodes. We found that ITS alone or combined with plastid regions showed the best discrimination across different infrageneric ranks and at species level. We suggest rbcL + matK + ITS as the first choice at present to barcode Primula plants. Although the present barcoding combination performed poorly in many closely related species of Primula, it still provided many new insights into current Primula taxonomy, such as the underlying presence of cryptic species, and several potential improper taxonomic treatments. DNA barcoding is one useful technique in the integrative taxonomy of the genus Primula, but it still requires further efforts to improve its effectiveness in some taxonomically challenging groups.

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and piezophototronics in low-dimensional wurtzite structure ZnO and GaN have been systematically studied. [8,9] The piezoresistive effect is that the band gap structure of the semiconductor can be changed by strain, which can modulate the transport behavior of materials. The piezoresistive effect have been investigated in low-dimensional materials such as silicon nanowire, [10] carbon nanotube, [11] and graphene. [12] The piezoresistive materials have been widely used for improving the transport properties of transistor and force sensor. [13] 2D materials have opened up unprecedented opportunities in the semiconductor industry, and have attracted significant attention due to their subnanometer size, unique structure, and unusual electronic properties offering future advancements in electronic, optoelectronic, sensor, catalysis, and energy field. [14][15][16] In 2012, the piezoelectric [17] and piezoresistive effects [18] were predicted in 2D transition metal dichalcogenides (TMDCs). Due to the piezoresistive effect, the band gap of 2D MoS 2 decrease with the increase of strain, the direct band gap of monolayer TMDCs change to indirect band gap when the stain is 1-2% and the semiconductor TMDC became a conductor when the strain was over 10%. The piezoresistive effect was observed in photo luminescence (PL) spectrum subsequently and the piezoresistive coefficient of 2D MoS 2 was measured. [19,20] The effect of strain on the transport behavior due to piezoresistive effect was investigated and the 2D MoS 2 piezoresistive tactile sensor was invented recently. [21,22] The breaking symmetry in specific lattice orientation of 2D TMDCs materials lead to the piezoelectric effect. In 2014, the piezoelectric effect was first observed in 2D MoS 2 flexible device and the piezoelectric coefficient of monolayer MoS 2 was measured by using an atomic force microscope apparatus. [23,24] The high sensitivity piezoelectric force sensor based on monolayer MoS 2 was also developed then. [25] The piezoelectric polarization charges generated by the piezoelectric effect can tune the Schottky barrier height (SBH) of a device and the electric field at the interface of a heterostructure, which can further improve the performance of optoelectronic. Recently, Wu et al. and Lin et al. utilized the piezoelectric effect to improve the properties of metal-MoS 2 photodetector and 2D MoS 2 /WSe 2 Van der Waals heterostructure. [26,27] However, study on taking advantage of the piezoelectric and piezoresistive effects simultaneously to improve the photoelectric performance of photodetector based on 2DThe mechanically stretchable 2D materials have attracted much interest for their potential applications in flexible electronics, as well as the possibility of strain-tuning their electronic and photoelectric performance through piezoelectric and piezoresistive effects. Piezoelectric and piezoresistive effects are observed in a flexible monolayer MoS 2 device and the effect of the strain on the photoelectric properties is investigated. The light-dark curre...

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