Phylogeography of Potentilla fruticosa (Rosaceae) in the Qinghai-Tibetan Plateau revisited: a reappraisal and new insights

Background: Most empirical studies to date have suggested that alpine plants in the central Qinghai-Tibetan Plateau (QTP) originated from the south-eastern QTP. However, previous phylogeographcial analysis of Potentilla fruticosa suggested that it diversified in the central QTP, which has also been assumed to have been a glacial refugium, and expanded to the north-eastern regions during the mid-Holocene period.

Aim: We reappraise this claim in the light of information acquired from sampling, haplotyping and analysing additional populations.

Methods: We sequenced the chloroplast trnT-L intergenic spacer of 346 individuals collected from 52 populations. We reconstructed phylogenetic relationships among haplotypes through Bayesian and Network analysis, and used several methods for demographic analysis.

Results: Some common and highly divergent haplotypes were distributed in the central, western and south-eastern QTP. Mismatch and other population genetic analyses applied to our data suggested that a distinct range expansion had occurred between approximately 30,000 and 325,000 years ago (kya).

Conclusions: Besides the possible postglacial expansion in the north-eastern QTP, our results further suggested that the range of the species radically expanded across the whole Plateau before the last glacial maximum (around 18 kya) and the south-eastern, western and central QTP regions had together provided important refugia during recent glacial stages. These findings, in contrast to the previous conclusions, highlight the importance of adequate sampling strategies in phylogeographical studies.     

Hydathode anatomy in Potentilla palustris (Rosaceae)

Guttating leaf teeth of Potentilla palustris plants from Wisconsin, USA, were cleared or processed for plastic sectioning or scanning electron microscopy. Anatomical features include: 1) long slender hydathode area occupying most of the tooth, 2) adaxial pad of small, flat epidermal cells with 50 or more sunken water pores about the size of ordinary abaxial stomates, 3) three converged bundles that extend distally, where their tracheary files are separated by intervening files of xylem parenchyma cells with sinuous walls, 4) adaxial mass of small, loosely arranged epithem cells above the xylem, 5) one slender phloem strand that extends only about a third of the way into the hydathode, and 6) bundle sheath extending distally only abaxially and along the flanks of the hydathode. Potentilla hydathodes differ significantly from non-guttating ones described earlier in Physocarpus (Rosaceae).     

Palynological study of Potentilla subg. Potentilla (Rosaceae) in the Western Mediterranean

A palynological study by LM and SEM was made of 26 taxa of Potentilla L. subg. Potentilla. It is more precise on material from 110 populations, mainly from the western Mediterranean. On the basis of morphometry, the subg. Potentilla can be said to have a stenopalynous nature, due to the absence of significant differences between the taxa studied and to the high degree of overlapping shown by their range of variation. With respect to ornamentation, which is striate, only P. rupestris pollen can be separately identified by a much more marked striation than the other species studied. An attempt was made to observe the taxonomic and phylogenetic relationships between the species of the natural groups of Potentilla on the basis of their pollen characters.     

Karyosystematic study of Potentilla L. subgen. Potentilla (Rosaceae) in the Iberian Peninsula

Chromosome numbers in 80 populations belonging to 18 species of Potentilla L. subgen. Potentilla from the Iberian Peninsula and two of P. maura, a North African endemic taxon, have been counted. The basic number of chromosomes is always x = 7 and these chromosomes are small (between 1 and 2 μm). For three species, the number of chromosomes is reported for the first time and, for another six, this number has been established in Iberian representatives. Moreover, new ploidy levels have been obtained for P. hispanica and P. crantzii with regard to their entire distribution area, and in P. cinerea and P. neumanniana for the Iberian Peninsula. Some taxonomic, phylogenetic and phytogeographic comments are made for several species or groups of species from the West Mediterranean region. In 13 species only one ploidy level has been found, but six species have several ploidy levels. Seven ploidy levels occur in the investigated taxa. The frequency of each ploidy level represented within Iberian Potentilla is analysed and the data are compared with those available for taxa from the rest of the distribution area of the genus.     

Potentilla basaltica (Rosaceae), a new species from Nevada

Potentilla basaltica Tiehm & Ertter is described, illustrated and compared to other members of theMultijugae group,P. newberryi, andIvesia. The leaf form and small flowers are reminiscent ofIvesia, indicating a possible new link between the two genera.     

Variation in Potentilla sect. Aureae (Rosaceae) in the Baltic states

The morphological variation of four Baltic representatives of the genus Potentilla section Aurea–P. neumanniana, P. arenaria, P. subarenaria and P. crantzii was studied with multivariate methods. Altogether 41 characters were used. The most important characters for the phenetical classification are those of the epidermis: characters of stellate and glandular hairs and numbers of cells. Macromorphological characters are less important, the most useful of these being the length of sepals and stipules and the number of teeth of the central leaflet. All four species are significantly distinct. Even P. subarenaria, a putative hybrid of P. arenaria and P. neumanniana, is clearly separated. At the same time, the species are morphologically quite variable, and it is possible to distinguish subclusters (morphotypes) within P. neumanniana, P. subarenaria and P. crantzii, which are also statistically distinct. The varieties described by Wolf (1908) under the name P. verna (P. neumanniana) do not agree well with the morphs in our material. However, it can be admitted that var. typica and var. neumanniana axe prevalent, var. pseudo-incis? and var. incis? occur occasionally; only var. longifoli? can be quite clearly delimited.     

Facultative apomixis and hybridization in arctic Potentilla section Niveae (Rosaceae) from Svalbard

The degree of sexual seed set and the ability to cross were investigated in three taxa of Potentilla section Niveae ( P. chamissonis , P. insularis and P. nivea ) from the Svalbard Archipelago. Emasculated and bagged flowers had little or no seed set, while 71% of the emasculated, bagged and pollinated flowers had some. The taxa are interpreted as pseudogamous apomicts. Parental plants and offspring were subjected to isozyme analysis. Most of the offspring were clones of the mother plant, but 1.7% had bands from the pollen donor. The sexual offspring were all produced by mother plants of P. insularis , which is interpreted as a facultative apomict. Surprisingly, crosses between different taxa gave higher seed to ovule ratios and numbers of sexually produced offspring than crosses within taxa. Some of the sexually produced hybrid offspring had the same kind of hairs on the petioles as their mother taxon, showing that hybrids may not be intermediate in hair characters, which are considered important in the delimitation of these taxa. The results of the present study indicate very close relationships among the investigated plants.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 142 , 373−381.     

The role of shrub (Potentilla fruticosa) on ecosystem CO2 fluxes in an alpine shrub meadow

Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO₂ sinks. On the plateau, alpine shrub meadow is one of typical grassland ecosystems. The major alpine shrub on the plateau is Potentilla fruticosa L. (Rosaceae), which is distributed widely from 3 200 to 4 000 m. Shrub species play an important role on carbon sequestration in grassland ecosystems. In addition, alpine shrubs are sensitive to climate change such as global warming. Considering global warming, the biomass and productivity of P. fruticosa will increase on Qinghai-Tibetan Plateau. Thus, understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau. However, the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear. The objectives of the present study were to evaluate the magnitude of CO₂ exchange of P. fruticosa shrub patches around the upper distribution limit and to elucidate the role of P. fruticosa on ecosystem CO₂ fluxes in an alpine meadow.Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity (NEP), ecosystem respiration (R e), and gross primary productivity (GPP) of P. fruticosa shrub patches at three elevations around the species' upper distribution limit. Ecosystem CO₂ fluxes and environmental factors were measured from 17 to 20 July 2008 at 3 400, 3 600, and 3 800 m a.s.l. We examined the maximum GPP at infinite light (GPP max) and maximum R e (R emax) during the experimental time at each elevation in relation to aboveground biomass and environmental factors, including air and soil temperature, and soil water content.Important findings Patches of P. fruticosa around the species' upper distribution limit absorbed CO₂, at least during the daytime. Maximum NEP at infinite light (NEP max) and GPP max of shrub patches in the alpine meadow varied among the three elevations, with the highest values at 3 400 m and the lowest at 3 800 m. GPP max was positively correlated with the green biomass of P. fruticosa more strongly than with total green biomass, suggesting that P. fruticosa is the major contributor to CO₂ uptake in the alpine shrub meadow. Air temperature influenced the potential GPP at the shrub-patch scale. R emax was correlated with aboveground biomass and R emax normalized by aboveground biomass was influenced by soil water content. Potentilla fruticosa height (biomass) and frequency increased clearly as elevation decreased, which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.     

金露梅与格桑花

青藏高原的格桑花是什么植物或者说是什么植物的花,存在广泛争议,困扰着想一探究竟的人们。格桑花作为一种精神存在于藏族百姓心中,是他们追求幸福吉祥和美好生活的情感象征,是重要的雪域文化标识,认识熟知并开发利用好它,将有助于推动藏区生态、文化和产业振兴。金露梅是青藏高原分布最广的树木,按集生羽状复叶小叶数可分为5叶金露梅和7叶金露梅,《中国植物志》对它们的记载分别是金露梅（Potentilla fruticosa L.）和小叶金露梅（P.parvifolia Fisch.）。通过对青藏高原植被和历史文化景观考察,结合当地藏民描述及地方传说,本研究认为格桑花就是金露梅,其分布海拔可以拓展到5200 m的高寒恶劣环境。金露梅生性强健,耐寒、耐旱、耐瘠薄、耐强光,象征着藏族同胞刚毅、坚强、勤劳质朴、不畏严寒、生命力顽强的品格。     

Morphological and genetic variations of Potentilla matsumurae (Rosaceae) between fellfield and snowbed populations

Identifying ecological factors associated with local differentiation of populations is important for understanding microevolutionary processes. Alpine environments offer a unique opportunity to investigate the effects of habitat-specific selective forces and gene flow limitations among populations at a microscale on local adaptation because the heterogeneous snowmelt patterns in alpine ecosystems provide steep environmental changes. We investigated the variation in morphological traits and enzyme loci between fellfield and snowbed populations of Potentilla matsumurae, a common alpine herb with a wide distribution along snowmelt gradients in northern Japan. We found significant differences in morphological traits between fellfield and snowbed habitats in a northern distribution region. These differences were maintained when plants were grown under uniform conditions in a greenhouse. Allozyme variations among 15 populations from geographically separated regions with different historical backgrounds showed that the populations are more genetically differentiated between the fellfield and snowbed habitats within a region than between populations occupying the same habitat type in different regions. These results suggest that variation in snowmelt regimes could be a driving force creating local adaptation and genetic differentiation of alpine plant populations.     

Morphometric analysis of Alaskan members of the genus Potentilla sect. Niveae (Rosaceae)

A morphometric study of Potentilla nivea, P unijlora, and P hookeriana, as well as the close relative of the latter, P furcata, has been carried out, and the quantitative data subjected to Canonical Discriminant Analysis. The four taxa belong to the arctic-alpine section Niveae of Potentilla, and material for the analysis was collected in Alaska, U. S. A. The a priori defined groups are based on petiole hair type, the qualitative, and only, character traditionally used to distinguish taxa within Potentilla sect. Niveae. The hair types recognized previously by taxonomists have been vaguely defined, and the intraspecific variation of other morphological characters has never been discussed. Ordination by canonical discriminant analysis was performed to characterize mean differences among species, to obtain insight into group differences, and to estimate character weights from correlations between canonical variates and original variables. The four taxa differ significantly in the canonical analysis of six quantitative characters. Leaflet length, incision depth (length of leaflet teeth), and ovule number are shown to be the most important discriminators. A key to the four taxa, taking into account the intra- vesus interspecific variation, as well as character weights, is provided.     

Refugia of Potentilla matsumurae (Rosaceae) located at high mountains in the Japanese archipelago

Molecular phylogeographic studies have revealed the genetic patterns and glacial-interglacial history of many plant and animal species. To infer the Quaternary history of alpine plants in the Japanese archipelago, which is poorly known, we investigated 203 individuals of Potentilla matsumurae and its varieties from 22 populations. We found 11 haplotypes based on approximately 1400 bp of two intergenetic spacers in chloroplast DNA (trnT-L and rpl20-rps20). The distribution of these haplotypes was geographically structured, which was supported by haplotype composition, principal component analysis, and unweighted pair group method with arithmetic mean (UPGMA), and N(ST) (0.71) was significantly greater than G(ST) (0.68). In addition to the positive correlation between genetic and geographic distance (Mantel test, r = 0.497, P < 0.001), an abrupt genetic change was detected between mountains in central Honshu and the Tohoku region. This genetic boundary was further supported by analysis of molecular variance (AMOVA), and high variation (54.0%) was explained by differences on either side of this boundary. Moreover, haplotypes in central Honshu were thought to have diverged, based on an outgroup comparison. These results suggest that mountains in central Honshu served as refugia during the Quaternary climatic oscillation, although the results could not reveal the history of most mountains in the Tohoku region and Hokkaido. Nevertheless, following floristic studies, our results indicate that alpine plants in Japan experienced a history different from that in Europe; i.e. they retreated into refugia during warm periods to avoid forest development, rather than glaciers.     

Repeated Range Expansion and Glacial Endurance of Potentilla glabra (Rosaceae) in the Qinghai-Tibetan Plateau

To date, little is still known about how alpine species occurring in the Qinghai-Tibetan Plateau (QTP) responded to past climatic oscillations. Here, by using variations of the chloroplast trnJ-L, we examined the genetic distribution pattern of 101 individuals of Potentilla glabra, comprising both the interior QTP and the plateau edge. Phylogenetic and network analyses of 31 recovered haplotypes identified three tentative clades (A, B and C). Analysis of molecular variance (amova) revealed that most of the genetic variability was found within populations (0.693), while differentiations between populations were obviously distinct (Fst = 0.307). Two independent range expansions within clades A and B occurring at approximately 316 and 201 thousand years ago (kya) were recovered from the hierarchical mismatch analysis, and these two expansions were also confirmed by Fu's Fs values and 'g' tests. However, distant distributions of clade C and private haplotypes from clades A and B suggest that they had survived the Last Glacial Maximum (LGM) and previous glaciers in situ since their origins. Our findings based on available limited samples support that multiple refugia of a few cold-enduring species had been maintained in the QTP platform during LGM and/or previous glacial stages.     

Molecules and morphology in concert: tests of some hypotheses in arctic Potentilla (Rosaceae)

We developed a combined molecular and morphological approach to unravel complex variation at low taxonomic levels, exemplified by some arctic members of Potentilla. Twenty-one populations from Svalbard were analyzed for random amplified polymorphic DNAs (RAPDs) and 64 morphological characters to test the hypotheses that (1) the P. nivea complex (section Niveae) consists of three taxa (P. chamissonis, P. insularis, and P. nivea), (2) three "eco-morphotypes" in P. pulchella (section Multifidae) should be considered different taxa, and (3) P. insularis originated as an intersectional hybrid (Niveae × Multifidae). Twenty-two RAPD multilocus phenotypes were observed in the 136 plants analyzed based on 35 markers. Three fairly distinct groups of RAPD phenotypes were identified in the P. nivea complex based on multivariate analyses and an analysis of molecular variance (AMOVA; 77.6% among-group variation). The variation within the P. nivea complex was more or less continuous in multivariate analyses of the morphological data. We identified, however, several individual morphological characters that separated unambiguously among the three groups of RAPD phenotypes, revealing that these groups correspond to the previously hypothesized taxa. Many identical RAPD multilocus phenotypes were observed in the "eco-morphotypes" of P. pulchella, suggesting that its conspicuous morphological variation is caused by plasticity or by genetic variation at a small number of loci. The hypothesis of the hybrid origin of P. insularis was not supported by the RAPD data. Overall, very little RAPD variation was observed within populations of the four taxa (2.1-16.7% in AMOVA analyses; average genotypic diversity, D, was 0.10-0.30). We conclude that detailed, concerted analysis of molecules and morphology is a powerful tool in low-level taxonomy.     

Molecular phylogeography and hybridization in members of the circumpolar Potentilla sect. Niveae (Rosaceae)

Glacial events and the formation of ice-free areas serving as refugia for plants and animals are important in shaping present patterns of genetic diversity in arctic areas. Beringia, situated in northeastern Russia and Alaska, has been pointed out as a major refugium. This study focuses on the historical biogeography of the circumpolar taxon Potentilla sect. Niveae. The taxonomy of the group is complex, most likely highly influenced by hybridization and apomixis. cpDNA microsatellites together with AFLP fragments were used to map the genetic variability in the section, from Beringia across the Canadian Arctic to Greenland. The data support the hypothesis that Beringia, as well as parts of adjacent arctic Canada, served as refugia during the Wisconsinan glaciation, and there is some evidence for a northern and a southern migration route out of Beringia. The hair type groups within sect. Niveae are more or less genetically distinct, and hybridization, especially with sect. Multifida, takes place. Haplotype diversity as well as frequency is at its maximum close to the Last Glacial Maximum ice cap edge. This pattern can be explained by merging of previously isolated refugia, by repeated extinction/colonization events close to the ice edge, and by hybridization among sympatric taxonomical lineages.     

Potentilla jiaozishanensis sp. nov. (sect. Leptostylae,Rosaceae) from southwest China

Potentilla jiaozishanensis, a distinct new species of Rosaceae from Yunnan, China, is described and illustrated. Morphologically, it is closely related to P. stenophylla var. stenophylla but clearly differs from the latter by its bidentate leaflets, lanceolate epicalyx‐segments that are longer than the sepals, villose ovaries and achenes. Moreover, the pollen grains of P. jiaozishanensis are markedly different from those of P. stenophylla var. stenophylla in size and shape. The newly described species is endemic to the Jiaozishan Mountains, southwest China.     

Karyomorphological study of the Spiraea japonica complex (Rosaceae)

Reported in this paper is a karyomorphological study on one natural population of each of eight varieties in theSpiraea japonica complex. The interphase and mitotic prophase can be classified into the simple chromocenter type and the proximal type, respectively. The metaphase karyotypes of the eight varieties were formulated as follows:S. japonica var.japonica: 2n=18=14m+2sm+2st;S. japonica var.acuta: 2n=18=11m+4sm+3st;S. japonica var.incisa: 2n=18=12m+4sm+2st;S. japonica var.stellaris: 2n=18=15m+1sm+2st;S. japonica var.acuminata: 2n=18=14m+2sm+2st;S. japonica var.ovalifolia: 2n=18=10m+2sm+2st+4t;S. japonica var.glabra: 2n=18=10m+4sm+4st;S. japonica var.fortunei: 2n=36=17m+16sm+3st. Karyomorphological study reveals that the chromosome numbers within the complex are stable, and that karyomorphological divergence between the varieties lies mainly in chromosome size and organization. Based on the karyomorphological data and geographical distribution of the complex, the differentiation pattern as well as evolutionary mechanism of the complex is evaluated.