Sex allocation in Cyananthus delavayi.Gynodioecy, where females and hermaphrodites coexist in the same natural population, is particularly suitable for predicting the ecological pressures that drive the stability of gender polymorphism. Since females have a disadvantage in that they only contribute to the next generation via ovules, they should gain an advantage via other means, of which resource allocation is an important component. Thus, to study their sex allocation is very helpful to understand how the dimorphic sexual system is maintained in natural systems. We studied the sex allocation patterns and reproductive output of the gynodioecious Cyananthus delavayi in three populations with different soil qualities (organic matter, N, P and K). The hermaphroditic flowers and pistils were much larger than those of female individuals. Although both gender morphs invested similar biomass in the pistils, females allocated more of their resource pool to the seed production, while hermaphrodites allocated more to pollinator advertisement. The pollen production of hermaphrodites did not differ between populations, suggesting that pollen production by hermaphrodites was not limited by soil nutrients. Fruit set of females, but not hermaphrodites, decreased with declining soil quality, whereas seeds per fruit of both females and hermaphrodites were highest in poor soils. Overall, this study shows that females achieve greater reproductive success by allocating more of their resource pool to enhancing seed production, which should favor their presence in gynodioecious populations. The hermaphrodites achieve reproductive success from both pollen and seed production, and unnecessarily reduce their allocation to pollen production. Soil quality should explain, at least partially, the sexual allocation patterns. Furthermore, some of our findings contradict previous hypotheses, thus adding a new example to the body of research on plant sex allocation and the development of future theories.

Cushion species occur in nearly all alpine environments worldwide. In past decades, the adaptive and ecosystem-engineering roles of such highly specialized life forms have been well studied. However, the adaptive strategies responsible for cushion species reproductive success and maintenance in severe alpine habitats remain largely unclear. In this study, we reviewed the current understanding of reproductive strategies and population persistence in alpine cushion species. We then present a preliminary case study on the sexual reproduction of Arenaria polytrichoides (Caryophyllaceae), a typical cushion species inhabiting high elevations of the Himalaya Hengduan Mountains, which is a hotspot for diversification of cushion species. Finally, we highlight the limitations of our current understanding of alpine cushion species reproduction and propose future directions for study.

Seed dormancy and germination characteristics are important factors determining plant reproductive success, and may be expected to have a major influence on plant distribution. In this study, we aimed to explore the characteristics of seed dormancy and germination in two endemic Rheum species (Rheum nobile and Rheum alexandrae) in the Himalaya-Hengduan Mountains. To determine the type of dormancy, fresh seeds of the two species (one population each) were incubated in light at 25/15 and 15/5 °C, and then dry after-ripening (DAR) seeds were incubated on water agar substrate with or without GA3. To determine the effect of temperature and light on germination, DAR seeds of the two species (two populations each) were incubated both in the light and in the dark at several temperatures, including constant and alternating temperatures. Base temperature (Tb) and thermal times for 50% germination (θ50) were calculated. DAR released physiological dormancy (PD), increasing final germination at 15/5 °C and widening the range of germination temperatures from higher to lower, indicative of type 2 non-deep PD for the two Rheum species. Light had no significant effect on germination of seeds from the two species (two populations each). Seeds of the two species germinated significantly better (>80%) at medium temperatures (10–25 °C) than at extreme low (5 °C) or high (35 °C) temperatures. Alternating temperatures (25/15 and 15/5 °C) did not significantly increase the final germination of the two species either in the light and in the dark, but it promoted seed germination more quickly than corresponding constant temperatures in the light in both Rh. alexandrae populations, especially at 15/5 °C. Germination in response to temperature was well described by the thermal-time model at suboptimal temperatures. The estimated Tb values were 1 and 0.9 °C, respectively, in two Rh. nobile populations; 4 and 4.1 °C, respectively, in two Rh. alexandrae populations; θ50 (thermal time) were 100 and 125 °Cd, respectively in two Rh. nobile populations; 76.92 and 83.33 °Cd, respectively in two Rh. alexandrae populations. The dormancy type, and germination responses to temperature and light condition does not explain why the two Rheum species are distributed in contrasting habitats. However, these findings reflect an advantageous germination strategy of these two Rheum species to adapt to the same alpine environments.

Sexual allocation pattern is considered highly relevant for the maintenance of females in the process of evolution from hermaphrodites to dioecy. Theoretical and empirical studies predict that gynodioecious plants should invest more resources in male function under harsher environments and/or when female frequency is higher; and that there are trade-offs between male and female function. We studied sexual allocation pattern in the gynodioecious species Cyananthus macrocalyx in two populations in SW China. The results showed that although the total flower mass in hermaphrodites was significantly higher than that in females, females and hermaphrodites allocated similar biomass to female function (pistil biomass). As a consequence, females allocated relatively more resource to female function, while hermaphrodites allocated relatively more resource to pollinator attractiveness. There was no difference in total flower mass, pistil mass, and pollen production in hermaphrodites between the two populations. These results suggest that the females compensate for the disadvantage of lacking male function by allocating relatively more resource to female function, while hermaphrodites gain fitness through both male and female functions. This study supports the idea that if females are to be maintained in a gynodioecious population, they must allocate more resource to female functions than is necessary for hermaphrodites. However, our results were in contrast to those of previous studies, in that trade-offs between male and female functions and male-biased allocation under high female frequency were not observed. This study adds to the body of research on plant sexual allocation, and for that it is, at least at some aspects, contrary to previous statements, it could be helpful for advancing the theoretical predictions in the future.

The Hengduan Mountains is the core of the Sino-Himalayan Floristic Region. Different views have been postulated from phylogeographic studies in understanding the historical biological events shaping present-day distributions and species diversities in this area. We analyzed the phylogeography of Rosa soulieana, a widely distributed rose species in dry and semi-dry valleys of the Hengduan Mountains of southwestern China using two cpDNA intergenic spacers. 9 cpDNA haplotypes were confirmed in 650 individuals from 39 populations, with the most dominant one existing in 36 populations. The relationship among the cpDNA haplotypes did not reflect the morphology-based intra-specific taxonomy of different varieties. There was very low cpDNA genetic diversity and relatively high population differentiation combined with lack of phylogeographic structure. The populations from Northwestern Yunnan, Southeastern Tibet and upper Yalongjiang River embraced most of the species genetic diversity, but with contribution of different historical effects. Northwestern Yunnan and upper Yalongjiang River appear to be the species refugia and centers of adaptive diversification, while Southeastern Tibet rather represents the species ‘melting pot’ in the Quaternary climate oscillations.

Knowledge of how germination and seedling establishment respond to soil water condition is crucial for plant conservation under global warming and land-use changes. We tested the flooding and drought tolerance of two plant species with different occurrences along a soil water gradient by assessing seed germination, seedling survival, seedling growth, and root characteristics. In the high Sino-Himalayas, Rheum alexandrae typically occurs in wetlands, R. nobile in scree or open slope with well-drained soils. Seeds and seedlings of the two species were subjected to different soil water conditions in controlled greenhouse experiments. Seed germination in both species was inhibited by high soil water content; however, seeds of R. alexandrae were more tolerant to flooding, especially to submergence. Seedling survival, biomass accumulation, root diameter, and root porosity of R. alexandrae increased significantly with increased soil water content, but submergence was lethal for seedlings. Seedling survival, biomass accumulation, and root length of R. nobile increased significantly in response to reduced soil water content. These results indicate that in the two species, seed germination and seedling establishment in response to different soil water condition are habitat-specific. Because both species are susceptible to moderate changes in soil water condition, their species-specific requirements with respect to this factor should be a consideration when planning their conservation.

Plant desiccation-related proteins (DRPs) were first identified as pcC13-62 from the resurrection plant Craterostigma plantagineum and it has been suggested they are involved in plant desiccation tolerance. We identified and characterized a plant DRP, which we called MS-desi, in the floral nectar of a subtropical bean species, Mucuna sempervirens (MS). MS-desi is a major nectar protein (nectarin) of the bean plant and expresses exclusively in the stylopodium, where the nectary is located. The full-length MS-desi gene encodes for a protein of 306 amino acids with a molecular mass of 33,248 Da, and possesses a ferritin-like domain and a signal peptide of 30 amino acids. Structural and phylogenetic analysis demonstrated MS-desi has high similarity to members of the plant DRPs, including pcC 13-62 protein. MS-desi has a similar hydropathy profile to that of pcC13-62 with a grand average of hydropathy index of 0.130 for MS-desi and 0.106 for pcC13-62 protein, which is very different from those of dehydrins and late embryogenesis abundant proteins. The protein’s secondary structures, both predicted from the amino acid sequence and directly analysed by far UV circular dichroism, showed that MS-desi is mainly composed of alpha helices and is relatively temperature dependent. The structure change is reversible within a wide range of temperatures. Purified MS-desi and raw MS floral nectar showed dose-dependent citrate synthase inhibition activity, but insensitivity to lactate dehydrogenase, suggesting that, unlike dehydrins, it does not act as a chaperone. The overall results constitute, to our knowledge, the first study on a desiccation-related protein in plant floral nectar.

Specialized bracts are thought to be important for the successful reproduction of some plants and are regarded as adaptations to diverse driving forces. However, few empirical studies have quantified the adaptive significance of bracts within a cost–benefit framework. We explored the adaptive significance of large and showy bracts for reproduction in Rheum nobile, a giant herb endemic to the high Himalayas. We examined whether the bracts enhance reproductive success during flowering and seed development. Bracts increased flower and fruit temperature on sunny days, greatly decreased the intensity of ultraviolet-B (UV-B) radiation reaching flowers and fruits, and prevented pollen grains being washed away by rain. Experiments indicated that high temperature could promote pollen germination, while pollen grains exposed to rain and UV-B radiation at ambient levels were seriously damaged. Furthermore, bract removal decreased the number of pollinators visiting flowers. When bracts were removed before or after flowering, fecundity and progeny quality were adversely affected, but seed predation by larvae of pollinators decreased. A cost–benefit analysis demonstrated that the cost of bracts, i.e., increased seed predation, is modest. Our results suggest that the bracts of R. nobile promote pollen germination, protect pollen grains from rain and intense UV-B radiation, enhance pollinator visitation during flowering, and facilitate the development of fertilized ovules during seed development. We conclude that multifunctional bracts of R. nobile are an effective adaptive strategy in alpine environments and might have been selected for because of abiotic environmental conditions as well as for enhancing pollination success.

The adaptations of alpine plants that enable them to survive in extreme environments are hotly debated. Floral traits are likely important since they are usually considered as evolutionary adaptations to pollinators, and thus to play a key role in the reproductive success of plants. In the subnival belt of the Hengduan Mountains (a globally important biodiversity hotspot with extreme environmental conditions in southwest China) plants show diverse floral morphologies. However, information on the flower diversity of this unique alpine ecosystem is scarce, especially at the regional scale. Therefore, using published information, herbarium collections and field observations, we have studied the sexual system and floral morphology of plants in the subnival belt of the Hengduan Mountains. Of the 823 species recorded in the region, 88.5 % are hermaphroditic (a particularly high proportion compared to floras of other regions). The flower morphology patterns indicate that showy flowers (attracting pollinators) and generalized floral traits (suited to a wide range of pollinators) are common in our study region. Some floral traits were clearly associated with each other among specialized flowers as well as among generalized ones. Our results identify key reproductive features of plants in the subnival belt of the Hengduan Mountains, and show how these plants might optimize their probability of pollination and thus maintain reproductive success. The study provides a foundation for further research on floral adaptation and plant–pollinator relationships in the study region.

Peracarpeae is a small tribe consisting of three genera: Homocodon, Heterocodon and Peracarpa, with a disjunct distribution between eastern Asia and western North America. Homocodon is endemic to southwestern China and was previously placed in the western North American genus Heterocodon. Our phylogenetic analysis using four plastid markers (matK, atpB, rbcL and trnL-F) suggests the polyphyly of Peracarpeae. Homocodon is sister to a clade consisting of the eastern Asian Adenophora, Hanabusaya and species of Campanula from the Mediterranean region and North America, rather than forming a clade with Heterocodon. Homocodon and its Eurasia relatives are estimated to have diverged in the early Miocene (16.84 mya, 95% HPD 13.35–21.45 mya). The eastern Asian Peracarpa constitutes a clade with the North American Heterocodon, Githopsis and three species of Campanula, supporting a disjunction between eastern Asia and North America in Campanulaceae. The Asian-North American disjunct lineages diverged in the early Miocene (16.17 mya, 95% HPD 13.12–20.9 mya). The biogeographic analyses suggest that Homocodon may be a relict of an early radiation in eastern Asia, and that Peracarpa and its closest North American relatives most likely originated from a Eurasian ancestor.

Following the rapid uplift of the Qinghai-Tibetan Plateau, the reorganization of the major river drainages in southwest China was primarily caused by river capture events. However, the impact of these past changes in drainage patterns on the current distribution and genetic structure of the endemic flora of this region remains largely unknown. Here we report a survey of amplified fragment length polymorphism (AFLP) in Terminalia franchetii, an endemic shrub or small tree of the deep and dry-hot river valleys of this region. We surveyed AFLP variation within and among 21 populations (251 individuals) of T. franchetii, distributed disjunctively between northern and southern drainage systems. Using STRUCTURE, principal coordinates analysis, and genetic distance methods, we identified two main population genetic groups (I and II) and four subgroups within the species, as follows: (I) the Upper Jinshajiang Valley (subgroup I(north)) and the Honghe drainage area (subgroup I(south)); (II) the Middle and Lower Jinshajiang and Yalongjiang Valleys (subgroup II(north)) and the Nanpanjiang drainage area (subgroup II(south)). Genetic diversity was lower in group I than in group II. According to the genetic diversity and genetic structure results, we suggest that the modern disjunctive distribution and associated patterns of genetic structure of T. franchetii result from vicariance caused by several historical drainage capture events, involving the separation of the Upper Jinshajiang, Yalongjiang and Daduhe from the Honghe or Nanpanjiang in southwest China.

We describe the elevational patterns of species richness and endemism of some important taxa in the Hengduan Mountains, southwest China. Species richness data came from publications, an online database, herbaria and field work. Species richness was estimated by rarefaction and interpolation. The Hengduan Mountains region was divided into a southern and northern subregion, and all species were assigned to four groups based on their distributional range within this region. The conditional autoregressive model (CAR) was used to relate species richness and explanatory variables. The elevational patterns of total, endemic and non-endemic species richness, at subregion and entire region scales, presented to be unimodal and peaked at similar elevations. Area size was strongly related with species richness, and was more powerful in explaining variation in species richness in the northern subregion than in the southern subregion. A single climatic variable (mean annual rainfall, potential evapotranspiration or moisture index) showed a weak relationship with the elevational pattern of species richness. Area and climatic variables together explained more than 67% of the variation in non-endemic richness, 53% in total richness, and 50% in endemic richness. There were three patterns of endemism at the generic level with increasing elevation: namely endemism increased, decreased, or peaked at middle elevations. All selected taxa have experienced rapid speciation and evolution within this region, which plays an important role in the uniform elevational patterns of total, endemic and non-endemic richness, and in the multiform elevational patterns of endemism.

The present paper analyzed 239 endemic genera in 67 families in the flora of seed plants in China. The results showed that there are five families containing more than ten endemic genera, namely, Gesneriaceae (27), which hereafter refers to the number of endemic genera in China, Composite (20), Labiatae (12), Cruciferae (11), and Umbelliferae (10), 15 families with two endemic genera, and another 30 families with only one endemic genus. Four monotypic families (Ginkgoaceae, Davidiaceae, Eucommiaceae and Acanthochlamydaceae) are the most ancient, relict and characteristic in the flora of seed plants in China. Based on integrative data of systematics, fossil history, and morphological and molecular evidence of these genera, their origin, evolution and relationships were discussed. In gymnosperms, all endemic genera are relicts of the Arctic-Tertiary flora, having earlier evolutionary history, and can be traced back to the Cretaceous or to the Jurassic and even earlier. In angiosperms, the endemic genera are mostly relicts, and are represented in all lineages in the “Eight-Class System of Classification of Angiosperms”, and endemism can be found in almost every evolutionary stage of extant angiosperms. The relict genera once occupied huge areas in the northern hemisphere in the Tertiary or the late Cretaceous, while neo-endemism mostly originated in the late Tertiary. They came from Arctic-Tertiary, Paleo-tropical-Tertiary and Tethys-Tertiary florisitic elements, and the blend of the three elements with many genera of autochthonous origin. The endemism was formed when some dispersal routes such as the North Atlantic Land Bridge, and the Bering Bridge became discontinuous during the Tertiary, as well as the climate change and glaciations in the late Tertiary and the Quaternary. Therefore, the late Tertiary is the starting point of extant endemism of the flora in China.

The leaf epidermis of all 23 species from Asian Buddleja was investigated with scanning electron microscopy (SEM). Characteristics of trichome type, stomatal shape, cuticular membrane on adaxial and abaxial epidermis, inner margin of outer stomatal ledge and ornamentation of outer stomatal ledge are presented in this study. Among the Buddleja species, some distinct epidermal patterns were observed. These can be used to characterize and identify different sections among the Asian Buddleja species, viz. Alternifoliae, Curviflorae and Rectiflorae. In general, stomatal length of Buddleja increases with ploidy level. This character can be used to distinguish diploids from polyploids without preparation of caryograms. Based on this correlation Buddleja microstachya, B. subcapitata and B. bhutanica are characterized to be diploids, as concluded from their stomatal dimensions. Leaf epidermis characters can also be used to differentiate species pairs that are easily confused with each other, viz., B. asiatica and B. bhutanica, B. albiflora and B. nivea, B. candida and B. fallowiana, B. delavayi and B. forrestii, B. japonica and B. lindleyana, B. officinalis and B. paniculata.

It has profound implications for species invasions and fitness, how weeds achieve reproductive success. We present the first study on the reproductive biology of Stellera chamaejasme, a toxic perennial weed which is abundant in the alpine meadows on the eastern Tibetan Plateau of China since the 1960s. S. chamaejasme has synchronogamy and herkogamous flowers, which last for about 11 days. Flowers can be yellow, white or reddish. Our results suggest that this species is self-incompatible and depends entirely on pollen vectors for seed production. All the pollinators observed were Lepidopteran species; however, the pollinator assemblage was significantly different among populations and likely independent on floral colour. Reproductive success and invasion of the weed might be a complex function of floral traits, breeding system and pollination ecology. Generally, plants with generalized pollination system are more invasive. However, our results suggest that specialized flowers and self-incompatibility in the present case may not prevent invasion of the weed.

To detect the horizontal pattern of phylogenetic structure shown by alpine plants, we measured phylogenetic structure using net related index (NRI) and net nearest taxon index (NTI), and analyzed the phylogenetic structure patterns of alpine plants along longitude, latitude and environmental gradients in the Hengduan Mountains Region (HDMR). Our results show that: 1) the phylogenetic structure tended to cluster with increasing latitude and longitude; 2) for NRI, latitude was closer related than longitude, while for NTI, longitude was closer related than latitude, though they both not significantly relate to NTI. The phylogenetic structure tended towards overdispersion in the southern HDMR, with good climate conditions of higher mean annual temperature and more mean annual precipitation. In contrast, with harsh climate conditions of lower mean annual temperature and less mean annual precipitation, the increasing environmental stress led to phylogenetic clustering in the northern HDMR. The results highlighted that in the alpine region of HDMR, environmental filters and geographical isolation had a great effect on the latitudinal and longitudinal alpine species distribution, respectively.

•Rodgersia is a rare example in which two early-diverging species occur at opposite ends of the distribution area.•Both incomplete lineage sorting and ancient introgression may be responsible for the discordant gene trees.•The contemporary biogeographic pattern of Rodgersia is more the result of rapid evolutionary changes of the species in the central area.The East Asian endemic genus Rodgersia comprises five species and several variants. These species exhibit variation in ploidy level and a fragmented distribution across the whole of East Asia. In order to explain their present distribution pattern under a robust phylogeny, we employed multiple copy nuclear genes (ITS and ETS), cpDNA (rpl32-trnL, trnV-ndhC, ndhF-rpl32) and a low copy nuclear gene (GBSSI) to reconstruct the species’ relationships within Rodgersia. Identification of ploidy levels was also carried out for most of samples. The early-diverging positions of R. nepalensis and R. podophylla were confirmed in different gene trees. Much topological incongruence among gene trees was found in the shallower branches, which comprised the species of central-southwest China. Both incomplete lineage sorting and ancient introgression may be responsible for the incongruent pattern observed. Ancient introgressions may have occurred between diploid species and the diploid progenitors of tetraploid species in different areas of southwest China. Rodgersia probably originated in Northeast Asia during the Pliocene. This genus is a rare example in which two early-diverging species occur at opposite ends of the distribution area, likely resulting from successive vicariance events. Unlike many vicariance events shaped simply by forest fragmentation during the Pleistocene, the contemporary biogeographic pattern of Rodgersia is more the result of rapid sympatric evolution (reticulate events and polyploidization) of the taxa in the central area.