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Cymbidium, which includes approximately 80 species, is one of the most ornamental and cultivated orchid genera. However, a lack of markers and sparse sampling have posed great challenges to resolving the phylogenetic relationships within the genus. In the present study, we reconstructed the phylogenetic relationships by utilizing one nuclear DNA (nrITS) and seven plastid genes (rbcL, trnS, trnG, matK, trnL, psbA, and atpI) from 70 species (varieties) in Cymbidium. We also examined the occurrence of phylogenetic conflict between nuclear (nrITS) and plastid loci and investigated how phylogenetic conflict bears on taxonomic classification within the genus. We found that phylogenetic conflict and low support values may be explained by hybridization and a lack of informative characteristics. Our results do not support previous classification of the subgenera and sections within Cymbidium. Discordance between gene trees and network analysis indicate that reticulate evolution occurred in the genus Cymbidium. Overall, our study indicates that Cymbidium has undergone a complex evolution., Highlights • A comprehensive understanding of Cymbidium phylogeny. • Reticulate evolution occurred in the genus Cymbidium. • Cymbidium has a complex evolution.

Bletilla guizhouensis (Coelogyninae, Epidendroideae, Orchidaceae), a new species from Guizhou, China, is described and illustrated in this study based on the morphological and molecular evidence. Based on the morphological comparison, B. guizhouensis is closely related to B. striata, but differs in having ovate-oblong floral bracts, oblong-elliptic dorsal sepal, lip broadly-obovate, lip mid-lobe subelliptic, and disk with 7 longitudinal lamellae. These features distinguish the new orchid from all other known species of Bletilla. Molecular analysis based on nuclear ribosomal ITS and plastid DNA sequence data indicate that B. guizhouensis is a new species.

Hydrogels are known as soft and wet materials. Development of metal-like hydrogels with super strong and malleable properties is highly desirable as it allows for broader application and reprocessability. Here we report a dual nanocomposite hydrogel with peculiar mechanical properties in water-poor region. The gel with water content of 35% exhibits excellent recovery and fatigue resistance with elongation at break exceeding 800%, while the gel with 15 wt% of water content shows an ultra-high compressive strength and modulus of more than 1 GPa. The dual nanocomposite structure and bound water endowed the gel with high strength. Besides, the gel modulus can be easily switched by temperature change in a reversible way due to hybrid crosslinking network of the hydrogel in which physical network breaks and reforms rapidly while chemical network remains the gel state. So the gel shows a force-driven softening behavior and can be molded into different shapes due to reversible thermo-induced modulus decline. The softening behavior is also beneficial for the self-healing of the gel. The peculiar mechanical properties make the hydrogel a potential candidate for a new generation of advanced engineering materials.

Paphiopedilum armeniacum is a rare and endangered lady’s slipper orchid in China. It is distributed around the mid-elevations of the Nu Mountains in southwest China. Due to over-harvest, habitat loss, and degradation, wild populations of P. armeniacum has declined drastically. A combination of approaches involving biotechnology, habitat restoration, and interspecific relationship reconstruction was used to carry out the reintroduction of the species. Integrated conservation program for this species included in-situ protection, ex-situ conservation, and reintroduction, which helped to rebuild a harmonious relationship between local farmers and P. armeniacum . The sustainable utilization of native plant resources in poor areas can promote regional sustainable development which is compatible with species protection.

Cymbidium erythraeum Lindl. is an endangered species of Orchidaceae and distributed in China and Bhutan, India, Myanmar, Nepal, and Vietnam. Here, we report the complete chloroplast (cp) genome sequence and the cp genome features of C. erythraeum. The complete chloroplast (cp) genome sequence of C. erythraeum is 156,327 bp in length and including one large single-copy region (LSC, 85,404 bp), one small single-copy region (SSC, 20,021 bp), and two inverted repeat regions (IRs, 25,426 bp). The cp genome encoded 136 genes, of which 107 were unique genes (80 protein-coding genes, 23 tRNAs, and four rRNAs). The phylogenetic relationships show that C. erythraeum is closely related to other species in the genus Cymbidium and is sister with C. tracyanum.

To enhance the fire safety of epoxy resins (EP) without affecting other properties, a novel organophosphorus compound named DDPPM has been synthesized and used as co-curing agent to obtain inherent flame-retardant EP. The Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), and 31P nuclear magnetic resonance (31P NMR) proven the successful synthesis of DDPPM. The mechanical results demonstrated that the mechanical properties of the epoxy resin did not deteriorate after adding DDPPM, and differential scanning calorimetry (DSC) shown that the glass transition temperature (Tg) of EP/DDPPM was maintained. Importantly, the EP/DDPPM presented satisfying flame-retardant efficiency in limiting oxygen index (LOI) and vertical burning tests. Incorporating 2 wt% DDPPM, the EP achieved the UL 94 V-0 rating and the LOI value was 31%. Meanwhile, the cone calorimeter (CC) test verified that DDPPM contributed to the reduction of heat and smoke release accompanied by increasing char yield. The thermogravimetric analysis/infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) and char analysis certified the flame inhibition and charring effect of DDPPM in EP.

To obtain a latent curing epoxy system with satisfactory thermal stability, flame retardance and dielectric properties, imidazolium dibenzo[c,e][1,2]oxaphosphate (IDOP) was synthesized by a facile way and utilized as a latent flame-retardant curing agent for epoxy resins (EP). It was confirmed that IDOP/EP one-pack system kept reactive inert near room temperature and cured efficiently under heating with a moderate heat release. The curing procedure was explored by X-ray photoelectron spectroscopy (XPS), confirming that the flame-retardant group was incorporated into epoxy chains by covalent and/or ionic bonds, hence the intrinsic flame retardance and excellent thermal stability were given to the cured resins finally. With only 15 wt% IDOP additions, the limiting oxygen index (LOI) increased to 37.0% from 20.5% of the reference sample, and UL-94 V-0 rating was achieved. The results of cone calorimetry test further certified that IDOP/EP showed satisfactory flame retardance dominating in gaseous phase, which was confirmed by the results of thermogravimetric analysis/infrared spectrometry (TG-IR). The thermal mechanical behavior of IDOP/EP was also evaluated by dynamic mechanical analysis (DMA). Especially, the incorporation of the flame-retardant group didn’t deteriorate the dielectric properties of the cured resin. Benefiting from the advances, the latent curing epoxy system with excellent comprehensive performance exhibited potential for versatile applications.

In an effort to overcome issues encountered in additive flame retardants for rigid polyurethane foams (RPUFs), a novel reactive flame-retardant triol (TDHTPP) based on a triazine and phosphate structure was designed and synthesized. This triol was chemically incorporated in the main chains of RPUFs as a chain-extender to prepare inherently flame-retardant RPUFs. TDHTPP showed good solubility in the polyols (polyol 4110 and PEG 400) of RPUF, making it convenient for industrial fabrication, such as in spay foaming. Excellent compatibility of TDHTPP with the polymer matrix endowed flame-retardant RPUFs (FR-RPUFs) much higher compressive strength than that of the neat RPUF, and a low thermal conductivity of ∼0.03 W/(m·K). Notably, with only 5 wt% of TDHTPP incorporated, the resultant RPUF displayed a UL-94 V-0 rating and more importantly, exhibited a great persistent flame retardancy during thermal accelerated aging tests at 140 °C for 96 h. Further characterization revealed that TDHTPP possessed both vapor-phase and condensed-phase flame-retardant behaviors, in which, vapor-phase action was dominant. This work provides a facile route to synthesize RPUFs with persistent flame retardancy, excellent thermal insulation and mechanical properties.

Herein, expandable graphite (EG) and aluminum hypophosphite (AP) are used to prepare flame-retardant polystyrene (PS) composites. The flame-retardant properties of the PS composites are investigated by the limiting oxygen index (LOI) test, vertical burning test (UL-94) and cone calorimetry test (CC). With 15 wt% EG or AP incorporated alone, the PS composites show limited improvement in LOI, and fail to pass the UL-94 test. In contrast, with 10 wt% EG and 5 wt% AP added, the sample (PS/10EG/5EG) passes the UL-94 V-0 rating, and its LOI value increases from 17% to 25.5%. CC results show that the PS/10EG/5AP has a significantly depressed peak heat release rate (PHRR) by 77.7%, total heat release (THR) by 39.3%, smoke product rate (SPR) by 78.2% and total smoke product (TSP) by 82.3%. Meanwhile, the flame-retardant mechanism of the PS composites is studied by SEM, XPS, TG-IR and Py-GC/MS, and the results of which indicating a combination of condensed-phase and gaseous-phase activity during combustion.

To overcome the poor compatibility, easy migration of additive flame retardants, a novel polyester polyol (DMOP) was synthesized from dimethyl methylphosphonate and diethanol amine through transesterification and used in the foaming formula to prepare inherent flame-retardant flexible polyurethane foams (FPUFs). DMOP mainly play soft segments in the foams which increases the flexibility and elongation at break. With a low incorporation amount of 10 php (ca. 6.3 wt%), the resultant FPUF can pass vertical burning test. More importantly, accelerated ageing tests at 140 °C for 64 h indicate the persistent flame retardancy of DMOP for FPUF. The thermogravimetric analysis (TGA) results reveal their lower thermal stability than that of ordinary polyurethane. The corresponding flame-retardant mechanism of DMOP-containing FPUFs is investigated by Pyrolysis gas chromatography and mass spectrometry (Py-GC/MS) and FTIR, which indicates the phosphorus in DMOP mainly played their role in the vapor phase. This work thus offers a facile route for preparing FPUFs with persistent, efficient flame retardancy.

A novel liquid phosphorus-containing polyol named as PDEO was prepared via reactions between ethylene glycol and phenylphosphonic dichloride. PDEO reacts with the -NCO-terminated prepolymers and forms urethane linkages in the chain extending reaction step, thus, it was used to prepare inherently flame-retardant flexible polyurethane foams (FPUFs). The structure and properties of flame-retardant FPUFs were characterized by scanning electron microscopy (SEM), tensile measurements, limiting oxygen index (LOI), vertical burning tests, cone calorimeter tests and thermogravimetric analysis (TGA). The vertical burning test demonstrated that fire extinguished instantly after the withdrawn of the pilot flame, while the PDEO loading was only 10 php. In addition, the persistent flame retardancy of PDEO in FPUFs was proved by thermal ageing test. The corresponding flame-retardant mechanism of PDEO-containing FPUFs was investigated by pyrolysis gas chromatography mass spectrometry (Py-GC/MS), X-ray photoelectron spectroscopy (XPS), SEM and FTIR, and the results indicated a gaseous phase dominated flame-retardant mechanism of PDEO.

Environmentally friendly flame-retardant coatings for fabrics urgently need to have both high efficiency and transparency, but their development faces severe challenges. In this study, we reported a highly flame-retardant coating without halogen and formaldehyde via a facile one-pot sol–gel approach derived from ammonium polyphosphate (APP), sodium alginate (SA), and tetraethoxysilane (TEOS). In this system, SA serving as a negatively charged stabilizer can effectively inhibit APP agglomeration and further co-gelatinize with TEOS, thus leading to high transparency (transmittance in the visible region >90%) and colorlessness of the coating. Meanwhile, SA as a charring agent, APP as both acid and blowing sources, and TEOS as a silicon source together constructed a P/N/Si-containing hybrid intumescent system, so that the coating showed highly flame-retardant efficiency for cotton fabric at an ultralow loading of 10 wt%, much superior to other coatings previously reported. The resultant cotton fabric showed a high limiting oxygen index of 31%, self-extinguishing ability in the vertical burning test. Additionally, the total heat release value and total smoke production significantly decreased by 63.5% and 70.0%, respectively in the cone calorimeter test, while the mechanical property remained almost unchanged. The mechanism analysis confirmed that the dense P/N/Si-containing graphitized char layer formed in the condensed phase could effectively prevent the release of heat and the diffusion of combustible gases. This work provides new insights into the design and fabrication of the flame-retardant coating combined with the advantages of high efficiency, environment friendliness, transparency, and colorlessness.

A highly efficient flame-retardant melamine salt (DPPMA) was synthesized from diphenylphosphinic acid (DPPA) and melamine (MA). The chemical structure of DPPMA was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, and elemental analysis, and the thermal degradation behavior was investigated by thermogravimetric analysis (TGA). Subsequently, flexible polyurethane foams (FPUFs) were prepared with DPPMA. Limiting oxygen index (LOI) tests, vertical burning tests, and cone calorimetric tests were carried out to investigate the combustion of the materials. The results showed that the FPUF with only 5 php DPPMA passed the vertical burning test and had an increased LOI value of 22%. The corresponding flame-retardant mechanism was systematically investigated by FTIR spectroscopy, TGA, and energy-dispersive X-ray (EDX) spectrometry. The results revealed that DPPMA released NH3 and H2O to dilute the combustible gas and phosphorus-containing radicals durin...

Gastrochilus Don (1825: 32.), subtribe Aeridinae (Orchidaceae), includes about 50 species, distributed from Southeast Asia to the Himalayas (Lucksom 2003, Jin et al. 2007, Shakya & Shrestha 2007, Chen et al. 2009). Generally, it is characterized by a saccate hypochile and two porate pollinia (Tsi et al. 1999). In China, about 30 species are found according to the most recent revision and recently published new species (Chen et al. 2009, Yi et al. 2010, Liu et al. 2016, Liu & Gao 2018).

In order to develop high-performance epoxy resins (EP), a novel phosphorus/nitrogen-containing phenylsiloxane macromolecule (DP-PPD) has been synthesized as a multi-functional additive. The DP-PPD macromolecules can simultaneously enhance the mechanical strength, flame retardancy, and smoke suppression performance for EP at low loading. Compared with unmodified EP, only by introducing 2 wt% DP-PPD, the impact strength, flexural strength and flexural modulus are greatly increased by 100%, 12.9% and 38.7%, respectively, due to flexible phenylsiloxane units and covalent interaction with EP matrix. Meanwhile, the resultant EP containing barely 3 wt% DP-PPD reaches V-0 rating in UL-94 test and shows a high limiting oxygen index of 30.1%. The cone calorimeter test results reveal that the peak of heat release rate, total heat release, and total smoke release of 9%DP-PPD/EP are decreased by 31.4%, 35.4%, and 20.0%, respectively, compared to those of unmodified EP. The mechanism analysis confirms that abundant aromatic rings, siloxane, and DOPO units in DP-PPD can synergistically promote the formation of P–Si-containing hybrid char layer for EP resins during combustion, thus leading to satisfied flame retardancy and smoke suppression. Meanwhile, the reduction of volatilized organic products and the emergence of phosphorous fragments indicates the flame inhibition effect of DP-PPD. Moreover, DP-PPD has little negative effect on the heat resistance of EP. This efficient single-component multi-functional additive provides a new strategy for the construction of high-performance macromolecular materials.

To expand the application of ammonium polyphosphate (APP) in epoxy resin (EP), hyperbranched polyethyleneimines (PEI) were selected to modify it via cation exchange reaction. Then, a highly-efficient flame-retardant hardener with poly-functionalities for EP was successfully prepared and named as PEI-APP. After curing, PEI-APP endowed the EP samples with good flame retardance and smoke suppression performance. Results suggested the total heat release (THR) and total smoke production (TSP) decreased 76.1% and 70.5% respectively. Thermogravimetric analyses (TGA) of the PEI-APP cured EPs displayed a slight improvement in the high temperature region compared with the reference sample (PEI/EP). Dynamic mechanical analysis (DMA) demonstrated that the glass transition temperature (Tg) of PEI-APP/EP also slightly increased compared with PEI/EP. Fourier transform infrared spectra (FTIR) was used to analyse the condensed products of PEI-APP/EP samples at different temperatures to investigate the flame-retardant mechanism. All the aforementioned results distinctly confirmed that PEI-APP did not only act as an effective flame-retardant hardener for EP, but also brought a good thermal stability and improved the smoke suppression to the system. This polyamine hardener provided a new platform for intumescent flame-retardant application in EP.

In this paper, an organic/inorganic phosphorus–nitrogen–silicon flame retardant (DPHK) was synthesized by Kabachnik-Fields reaction and the sol-gel method, then it was used as a reactive flame retardant to prepare flame-retardant and smoke-suppressant epoxy resins (EP). The influence of DPHK on the flame retardancy of EP was investigated by limiting oxygen index (LOI), vertical burning test (UL-94 V) and cone calorimeter (CC) test. The results revealed that the EP containing only 3 wt% DPHK achieved UL-94 V-0 rating, and the corresponding LOI value reached 29%. Furthermore, the cone calorimeter results demonstrated that the DPHK effectively reduced the heat release rate (HRR) and total release rate (THR) of the EP. Compared with EP, the peak of heat release rate (PHRR) and THR of 4%DPHK-EP reduced by 36% and 30%, respectively. More importantly, the incorporation of DPHK suppressed the release of toxic fuel (CO) and smoke of EP, meanwhile, the increased char residue and CO/CO2 ratio of the DPHK-EP samples proved that DPHK presented not only the condensed-phase activity but also gas-phase activity. Furthermore, the involved gases and char residues were studied by using thermogravimetric analysis coupled with coupled with Fourier transform infrared spectrometry (TG-FTIR), pyrolysis gas chromatography/mass spectrometry (Py-GC/MS), scanning electronic microscope together with the energy dispersive X-ray spectrometer (SEM-EDX) and X-ray photoelectron spectroscopy (XPS). The results certified the charring effect of the phosphaphenanthrene group and the enhancing effect of the silicon group. Subsequently, the flame inhibition effect and lesser combustible gases release enhanced the flame-retardant properties of EP.

The construction of fully bio-based epoxy resins (EP) has been of particular interest in both academia and industrial circles for years; among these, epoxidized soybean oil (ESO) derived thermosets have received the most attention, but they usually exhibit poor performance due to their flexible fatty chains. Herein, tannic acid (TA), with its great degree of functionality and massive aromatic structures, was chosen as the multi-phenol curing agent for ESO to prepare fully bio-based EP thermosets with a high relaxation temperature and satisfactory mechanical properties. As a natural 2-substituted imidazole-containing substance, histidine (H) was used as the curing accelerator under moderate curing conditions (120–180 °C). This EP system showed high curing activity and a good curing degree while operating. The cured thermosets were found to be thermally stable (T5% > 270 °C) and displayed a high relaxation temperature (77 °C) with a tensile strength of 23 MPa. Preliminary adhesion tests showed that the cured product exhibited a high lap-shear strength of about 19 MPa in adhesion failure mode. Taking these advantages into account, this kind of fully bio-based EP could introduce more chances for versatile applications, such as being used in structural materials and construction adhesives.

In this manuscript, flame-retardant and smoke-suppressant flexible polyurethane foams (FPUFs) were designed and synthesized based on novel liquid phosphorus-containing polyol named as PDEO and expandable graphite (EG). The reactive PDEO can be chemically added into the chain of FPUF, while expandable graphite was blended into the matrix of foam through foaming process. Benefitting from the incorporation of reactive PDEO with a long chain, the resultant FPUF containing EG exhibited considerable mechanical properties. More importantly, the synergistic effect of PDEO and EG can endow FPUF with great flame retardancy, anti-driping performances. Furthermore, the resultant FPUF/EG/PDEO foams exhibit considerable smoke suppression performances. The vertical burning test revealed that the FPUF containing 5 php PDEO and 10 php EG extinguished quickly without dripping and kept the original shape after removing the igniter. The cone calorimeter results demonstrated that the synergistic effect of PDEO and EG can effectively reduce the heat release rate (HRR) and total release rate (THR) of the composite foam. Remarkably, the smoke production release (SPR), total smoke production (TSP), light transmission and specific optical density results indicated significantly smoke-suppressant properties of the composite foam. The mechanism analysis confirmed that the synergistic effect of gas-condensed bi-phase action from PDEO and EG contributed the great flame retardation of the composite foam. This novel FPUF provides a promising strategy for producing the polymer foam with flame retardation, smoke suppression and anti-dripping performances.

Pholidota imbricata belongs to tribe Coelogninae in Orchidaceae distributed in Sichuan, Xizang, and Yunnan. Here, we report the first complete chloroplast (cp) genome and the cp genome features of P. imbricata. The complete cp genome sequence of P. imbricata is 159,292 bp in length and presented a typical quadripartite structure including one large single-copy region (LSC, 87,515 bp), one small single-copy region (SSC, 20,999 bp), and two inverted repeat regions (IRs, 25,389 bp each). The cp genome encoded 141 genes, of which 108 were unique genes (80 protein-coding genes, 24 tRNAs, and 4 rRNAs). The phylogenetic relationships show that P. imbricata is sister to the species of the genus Pleione in tribe Coelogninae.

Dendrobium thyrsiflorum H. G. Reichenbach ex André is an endemic herb with ornamental and medicinal orchid value distributed in Southeast of Yunnan of China. Here, we report and characterize the complete chloroplast (cp) genome sequence of D. thyrsiflorum in order to provide genomic resources helpful for its identification, conservation and utilization. The complete cp genome of D. thyrsiflorum is 160,123 bp, including one large single-copy region (LSC, 88,001), one small single-copy region (SSC, 21,142), and two inverted repeat regions (IRs, 25,490). The cp genome contains 143 genes, consisting of 110 unique genes (80 protein-coding genes, 26 tRNAs, and 4 rRNAS). The phlyogenetic relationships show that D. thyrsiflorum is closely related to other species of Dendrobium.

Pendulorchis gaoligongense G. Q. Zhang, K. Wei Liu & Z. J. Liu var. lushuiensis L. J. Chen, X. C. Shi & W. H. Rao (Orchidaceae, Vandeae) is described and illustrated as a new variety from Yunnan, China. It differs from the typical variety, P. gaoligongense, by having shorter leaves that are 30–40 cm, smaller flowers that are 4–5 mm diameter, and a reddish white perianth (vs. leaves 40–60 cm, flowers 8–9 mm diameter, and a purple-red perianth).

In this work, 2-carboxyethyl(phenyl)phosphinic acid melamine salt (CMA, phosphorus valence +1), melamine hypophosphite (MHPA, phosphorus valence +1), melamine phosphite (MPOA, phosphorus valence +3), and melamine pyrophosphate (MPyP, phosphorus valence +5) were respectively used as flame retardants for flexible polyurethane foam (FPUF), and fire performance as well as pyrolysis behaviors of FPUF were investigated systematically. CMA and MHPA were found to have better flame retardance than MPOA and MPyP for FPUF, which mainly played a role in the gas phase due to the release of many phosphorus-containing volatiles and melamine derivatives. The types of phosphorus-containing gaseous pyrolysis products of CMA were much more than that of MHPA due to the different chemical moieties surrounding the phosphorus atom, which made it have the highest flame-retardant efficiency for FPUF. Besides this, the possible thermal degradation mechanisms of CMA and MHPA were proposed.

A new orchid species, Cheirostylis wenshanensis (Orchidaceae; Cranichideae; Goodyerinae), from Yunnan Province, China, is described and illustrated based on morphological. This new species is similar to C. pingbianensis, but it differs by having a leaf-like flora bract at bottom, to 2.3 cm long; Inflorescence raceme with 5 flowers; The rest part of lateral sepal 2.8–3 mm, front of lip 5–6 × 5–6 mm, both with 1 pale green spot at base of lip lobes, without denticulate between lobes.

A new orchid species, Cymbidium shidianense (Orchidaceae; Cymbidieae), from Yunnan Province, China, is described and illustrated based on morphological and molecular analyses. This new species is similar in morphology to C. cyperifolium, but it differs in its larger pseudobulbs, rigid leaves, broader pale green sepals, petals with darkly coloured veins and set of V-shaped blotches on the lip midlobe. A phylogenetic analyses based on nuclear ribosomal ITS and plastid (matK, rbcL) DNA sequence data support C. shidianense as related to C. cyperifolium.

A new orchid species, Cymbidium densiflorum , from Yunnan, China, is described and illustrated here based on morphological and molecular analyses. A detailed comparison between the newly discovered orchid and other members of Cymbidium was conducted. The new plant belongs to C . section Cymbidium and has a pendent inflorescence, thick-coriaceous flowers with two pollinia and rigid leaves, and it differs greatly from all other known species of this section by being a large plant bearing leaves with an acute, oblique apex and producing a long inflorescence with more than 30 purplish brown large flowers, in which the lateral sepals are oblique and narrowly elliptic with a tooth at the apex and narrowly ovate-elliptic petals . A molecular study based on the nuclear ribosomal ITS and plastid matK , rbcL , trnG , trnL and atpI DNA sequence data indicated that C. densiflorum is sister to C. paucifolium .

A new pollination mechanism is reported of an orchid species, Bulbophyllum penicillium, based on a field observation in Southeast Yunnan of China. This species has a sensitive lip, and there is a distance of 2–3 mm between it and column apex. Once the lip is touched by a landing insect, it will move up and down or swing left and right continuously, just like a moving caterpillar. By suck a lip movement, the pollinator, a very small fruit fly (Drosophila sp.) ca. 1 mm in height, will be pressed toward the column apex where anther and stigma are located, and then cross-pollination takes place. This unique mode of pollination, depending on the movement of lip rather than insect itself, has never been found before in either Orchidaceae or other families of angiosperms.

Outbreeding is usually advantageous because inbreeding suffers from depression. Nevertheless, mixed mating is very common in nature. We found two co-existing plant types, self-compatible and self-incompatible, in populations of the orchid Bulbophyllum orientale. The floral parts of this plant form a device to promote cross-pollination. Rancid substances are excreted to lure pollinators to the labellum, and pollens are attached to pollinators through a delicate mechanism. Given that many inflorescences and flowers are present on a clone and each inflorescence, respectively, pollinating insects may continuously visit inflorescences of the same clone and flowers of the same inflorescence but rarely continuously visit different populations separated by large distances. Consequently, self-compatible plants produce seeds from both crossing and selfing, and self-incompatible plants only bear crossing seeds. Thus, a crossmixed mating system is created in the population. Individuals capable of producing both crossed and selfed seeds have better chances in natural selection. The strict crossing system is broken down, and a cross-mixed mating system consisting of both mixed mating and strict crossing is formed. The cross-mixed mating system fluctuates with varying behavior of pollinating insects. The mixed mating system is favored because a population has many clone individuals and because each individual has many multi-flower inflorescences in B. orientale. The partial strict crossing is retained, and it can counteract the latent harm caused by selfing and assist in the maintenance of this cross-mixed mating system. The successful evolution of flowering plants is demonstrated by the mode of attraction for pollinating insects, the smart use of the cross-pollinating facility, and the tradeoff between crossing and mixed mating.

Background Outcrossing is known to carry genetic advantages in comparison with inbreeding. In many cases, flowering plants develop a self-incompatibility mechanism, along with a floral component adaptation mechanism, to avoid self-pollination and to promote outbreeding. Orchids commonly have a lip in their flower that functions as the a visiting plate for insect pollinators. Aside from the lip, however, many species (including Coelogyne rigida) have sheaths around the axis of inflorescence. The function of these sheaths remains unknown, and has long been a puzzle to researchers. Methodology/Principal Findings We investigated the function of these sheaths in relation to the lip and the pollinators, as well as their role in the modes of pollination and reproduction of Coelogyne rigida in 30 flowering populations of orchids in the limestone area of Southeast Yunnan, China. We found that self-incompatible C. rigida developed specialized bird perches around the basal axis of inflorescence to attract sunbirds and to complement their behavioral tendency to change foraging locations frequently. This self-incompatibility mechanism operates separately from the floral component adaptation mechanism. This mechanism thus prevents bees from repeatedly visiting the floral lip of the same plant which, in turn, results in autogamy. In this way, instead of preventing autogamy, C. rigida responds to these negative effects through a highly efficient cross-pollination method that successfully transfers pollen to different plants. Conclusions The proposed method ensures reproductive success, while offsetting the infertile self-pollination by insects, thereby reducing mating costs and addressing the lack of cross-pollination. The adaptation provides a novel and striking example of structural adaptation that promotes cross-pollination in angiosperms.

BACKGROUND: Holcoglossum is a small orchid genus of 12 species ranging from SW China to Thailand and NE India. Although molecular and morphological analyses have been performed to establish the phylogenetic relationships within this genus, the interspecific relations and its relations with allied genera, such as Rhynchostylis, Aerides and Vanda, remain unclear. METHODOLOGY/PRINCIPAL FINDINGS: In addition to morphological analysis, maximum parsimony, maximum likelihood, and Bayesian inference analyses were performed based on fragments of the nuclear ITS and chloroplast trnL-F and matK genes of 31 taxa (15 Holcoglossum, 14 Aeridinae, 2 outgroups) representing all major clades of the Holcoglossum alliance. The results suggest that Holcoglossum is triphyletic, comprising three clades: the Holcoglossum clade, its sister clade, and a distant clade more closely related to Rhynchostylis, Aerides, and Vanda than to the Holcoglossum clade. The Holcoglossum clade is further divided into three subclades; the genetic distances between these three subclades also support this delimitation. The molecular conclusion is consistent with their distinct morphological characters. CONCLUSIONS: We propose that the latter two clades comprise two new genera, Paraholcoglossum and Tsiorchis, and Holcoglossum clade divides into three sections. In addition, a new section, Holcoglossum sect. Nujiangensia, and a new species, Holcoglossum linearifolium, are proposed. Some new combinations are made, and a new scheme is provided for the classification of all species of Holcoglossum, Paraholcoglossum, and Tsiorchis.