The role of dissolved organic matter (DOM) quality in the growth enhancement of Alexandrium fundyense (Dinophyceae) in laboratory culture1

Several algal species responsible for harmful algal blooms (HABs), such as Alexandrium fundyense, are mixotrophic under certain environmental conditions. The ability to switch between photosynthetic and heterotrophic modes of growth may play a role in the development of HABs in coastal regions. We examined the influence of humic dissolved organic matter (HDOM) derived from terrestrial (plant/soil) and microbial sources on the growth of A. fundyense. We found that a terrestrially derived HDOM, Suwannee River humic acid (SRHA), did enhance A. fundyense growth; however, a microbially derived HDOM, Pony Lake fulvic acid (PLFA) did not enhance growth. A. fundyense grows in association with bacteria in culture and we observed that bacterial cell densities were much lower in A. fundyense cultures than in bacteria‐only cultures, consistent with bacterial grazing by A. fundyense in culture. In bacteria‐only cultures with added algal exudates (EX), the addition of PLFA and SRHA resulted in a slight increase in bacterial cell density compared to cultures without HDOM added. Changes over time in the chemical quality of the HDOM in the A. fundyense cultures reflected contributions of microbially derived material with similar characteristics as the PLFA. Overall, these results suggest that the chemical differences between SRHA and PLFA are responsible for the greater effect of SRHA on A. fundyense growth, and that the differential effect is not a result of an effect on the growth of associated bacteria.     

Life cycle size dynamics in Didymosphenia geminata (Bacillariophyceae)

Didymosphenia geminata has received a great deal of attention in the last 25 years, and considerable effort has gone into determining the origin, ecological impact, and economic consequences of its invasive behavior. While environmental conditions are a controlling influence in distribution, the extreme success of the species may be tied to its basic biology and life history. Little is known, however, about population dynamics, size restoration and reproduction of D. geminata. The objective of this study was to determine the temporal patterns in cell size frequency, size restoration strategy, and synchronization of life cycles between populations in close proximity. We implemented FlowCam technology to measure the length of more than 100,000 D. geminata cells from two sites in South Boulder Creek, Colorado over 1 year. We applied finite mixture modeling to uncover temporal patterns in size distribution. Our results show that collections of D. geminata exhibited a complex, multimodal size distribution, almost always containing four overlapping age cohorts. We failed to observe direct visual evidence of the sexual phase. Multiple abrupt and directional shifts in size distribution, however, were documented providing conclusive evidence of cell size restoration. Lastly, nodules in close proximity were asynchronous with respect to size frequency profiles and size diminution, highlighting the relevance of spatial heterogeneity in in situ diatom size dynamics. This study is the first to document the complexity of diatom cell size distribution in a lotic system, size restoration in D. geminata, and the variability in rates of size reduction at microhabitat spatial scales.     

Phylogenetics and comparative analysis of the mitochondrial genomes of three violet‐ringed octopuses

Similar morphological characters and little molecular data of Amphioctopus rex, A. neglectus and A. cf. ovulum resulted in their unknown phylogenetic statuses and equivocal relationships. In this study, the complete mitochondrial genomes of these three species collected in Chinese waters were sequenced and compared with each other to clarify the relationships among them. The lengths of the mitochondrial genomes varied from 15,646 bp to 15,814 bp, and the A + T content and GC skew for protein‐coding genes showed little variation. In contrast, both a dendrogram based on codon usage and the gene arrangements of the three octopuses showed that A. rex was more closely related to A. neglectus than to A. cf. ovulum. Five data sets and two methods (maximum likelihood and Bayesian inference) were utilized for the first time to explore the phylogenetic relationships among these three species in Octopodidae. The results indicated that a data set combining protein‐coding genes and RNA genes (PR) was optimal for analysing the relationships among 43 cephalopods. All of the phylogenetic trees divided the cephalopods into 10 taxa and supported the monophyly of Oegopsida, Myopsida, Sepiidae and Octopodidae. In this study, Idiosepiidae was classified as sister to Sepiolidae. Trees constructed using all data sets robustly supported the monophyly of the genus Amphioctopus. Notably, A. rex was more closely related to A. neglectus than to A. cf. ovulum, although these three species share the characteristic of violet rings on dark ocelli.     

Identification of species and materia medica within Angelica L. (Umbelliferae) based on phylogeny inferred from DNA barcodes

DNA barcodes have been increasingly used in authentication of medicinal plants, while their wide application in materia medica is limited in their accuracy due to incomplete sampling of species and absence of identification for materia medica. In this study, 95 leaf accessions of 23 species (including one variety) and materia medica of three Pharmacopoeia‐recorded species of Angelica in China were collected to evaluate the effectiveness of four DNA barcodes (rbcL, matK, trnH‐psbA and ITS). Our results showed that ITS provided the best discriminatory power by resolving 17 species as monophyletic lineages without shared alleles and exhibited the largest barcoding gap among the four single barcodes. The phylogenetic analysis of ITS showed that Levisticum officinale and Angelica sinensis were sister taxa, which indicates that L. officinale should be considered as a species of Angelica. The combination of ITS + rbcL + matK + trnH‐psbA performed slight better discriminatory power than ITS, recovering 23 species without shared alleles and 19 species as monophyletic clades in ML tree. Authentication of materia medica using ITS revealed that the decoction pieces of A. sinensis and A. biserrata were partially adulterated with those of L. officinale, and the temperature around 80 °C processing A. dahurica decoction pieces obviously reduced the efficiency of PCR and sequencing. The examination of two cultivated varieties of A. dahurica from different localities indicated that the four DNA barcodes are inefficient for discriminating geographical authenticity of conspecific materia medica. This study provides an empirical paradigm in identification of medicinal plants and their materia medica using DNA barcodes.     

Effects of algal food quality on sexual reproduction of Daphnia magna

The objective of our study was to investigate sexual reproduction of Daphnia magna associated with mating behaviors and hatching rates, according to different algal food sources. Since a diatom is known to contain more abundant long‐chain poly unsaturated fatty acids (PUFAs), we hypothesized that the diatom‐consuming D. magna would exhibit more successful reproduction rates. Upon the hypothesis, we designed three experiments using two algal species, a green alga (Chlorella vulgaris) and a diatom (Stephanodiscus hantzschii). From the results, we found that the mating frequency and copulation duration increased in the treatment with S. hantzschii, resulting in a significant increase of hatching rates of resting eggs. In the other two repetitive mating strategies (e.g., one female vs. multiple males, and one male vs. multiple females), we found that the hatching rates of resting eggs were greater in the S. hantzschii treatment. In addition to the mating strategy, male body size significantly increased in the diatom treatment, hence average diameter of penis was also statistically different among the treatments (greater diameter in the S. hantzschii treatment). To examine the effect of algal food quality, we estimated quantity of fatty acids in the two algal species. Our result showed that S. hantzschii had a higher proportion of long‐chain PUFAs than C. vulgaris. Furthermore, a stable isotope analysis revealed that carbon and nitrogen originated from S. hantzschii were more assimilated to D. magna. In summary, our study manifested that diatom consumption of D. magna leads to more successful sexual reproduction. We then discussed how the diatom consumption of zooplankton influences food web dynamics in a freshwater ecosystem.     

Responses of a native plant species from invaded and uninvaded areas to allelopathic effects of an invader

Invaders exert new selection pressures on the resident species, for example, through competition for resources or by using novel weapons. It has been shown that novel weapons aid invasion but it is unclear whether native species co‐occurring with invaders have adapted to tolerate these novel weapons. Those resident species which are able to adapt to new selective agents can co‐occur with an invader while others face a risk of local extinction. We ran a factorial common garden experiment to study whether a native plant species, Anthriscus sylvestris, has been able to evolve a greater tolerance to the allelochemicals exerted by the invader, Lupinus polyphyllus. Lupinus polyphyllus produces allelochemicals which potentially act as a novel, strong selective agent on A. sylvestris. We grew A. sylvestris seedlings collected from uninvaded (naïve) and invaded (experienced) sites growing alone and in competition with L. polyphyllus in pots filled with soil with and without activated carbon. Because activated carbon absorbs allelochemicals, its addition should improve especially naïve A. sylvestris performance in the presence of the invader. To distinguish the allelochemicals absorption and fertilizing effects of activated carbon, we grew plants also in a mixture of soil and fertilizer. A common garden experiment indicated that the performances of naïve and experienced A. sylvestris seedlings did not differ when grown with L. polyphyllus. The addition of activated carbon, which reduces interference by allelochemicals, did not induce differences in their performances although it had a positive effect on the aboveground biomass of A. sylvestris. Together, these results suggest that naïve and experienced A. sylvestris plants tolerated equally the invader L. polyphyllus and thus the tolerance has not occurred over the course of invasion.     

Stimulated rejuvenation of dormant Aulacoseira granulata (Bacillariophyta) by Gloeocystis planctonica (Chlorophyta) in a eutrophic river

The abundance of Aulacoseira granulata (Ehrenburg) Simonsen and Gloeocystis planctonica (West & G.S.West) Lemmermann was assessed during the summers of 2005 and 2010 in the eutrophic Fox River, Wisconsin, USA. In both years, a mid‐summer bloom of G. planctonica was followed by the rapid growth of A. granulata. Laboratory experiments in which A. granulata was grown in cell‐free filtrate of a G. planctonica culture revealed that the growth of A. granulata was stimulated in the G. planctonica‐treated medium relative to controls. This effect was detected when dormant A. granulata cells were used as the source culture for the experiment but not when actively growing cells were used. Dormant A. granulata also grew more rapidly in river water collected after the 2010 G. planctonica bloom relative to river water collected before the bloom. These results suggest that the summer bloom of A. granulata in the river was stimulated by G. planctonica. This relationship can be described as stimulated rejuvenation, an interaction where the transition of an algal resting stage into active growth is triggered by exposure to another species.     

Variation in Polyphenolic Profiles,Antioxidant and Antimicrobial Activity of Different Achillea Species as Natural Sources of Antiglycative Compounds

A comparative study was carried out on the methanolic extracts from six Achillea species and the examined polyphenols from these plants on the formation of advanced glycation end‐products (AGE) in vitro. A. pachycephala which was richer in flavonoids (15 mg quercetin/g W) and phenolics (111.10 mg tannic acid/g DW) with substantial antioxidant activity (IC₅₀ = 365.5 μg/ml) presented strong anti‐AGE properties. Chlorogenic acid, luteolin, quercetin and caffeic acid were identified as the major polyphenols in the extracts by HPLC. In general, polyphenolic content follows the order of A. pachycephalla > A. nobilis > A. filipendulina > A. santolina > A. aucheri > A. millefolium. Most extracts exhibited marked anti‐AGE ability in the bovine serum albumin (BSA)/methylglyoxal (MG) system, though A. pachycephala showed the highest potential. The formation of AGEs was assessed by monitoring the production of fluorescent products and circular dichroism (CD) spectroscopy. Diminution in free radical production (assessed by 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assays) is discussed as potential mechanism for delay or reduced AGE. The results demonstrate the antiglycative, antioxidant and antimicrobial potential of Achillea species which can be attributed to polyphenols content and the effectiveness on generation of AGEs, thus Achillea species can be considered as natural sources for slowing down glycation related diseases.     

Morphology and Phylogeny of Three Pseudovorticella Species (Ciliophora: Peritrichia) from Brackish Waters of China

The biodiversity of peritrich ciliates from brackish biotopes is rarely investigated, especially members of the genus Pseudovorticella. Here, the morphology of three species of Pseudovorticella, i.e. P. cf. vestita (Stokes, 1883) Jankowski, 1976, P. spathulata sp. n., and P. qinghaiensis sp. n. isolated from brackish waters were studied. Pseudovorticella cf. vestita is characterized by inverted bell‐shaped cell; a J‐shaped macronucleus; a single contractile vacuole ventrally located; P3 three‐rowed; pellicle striated with highly developed pellicular vesicles; 18–22 transverse silverlines between peristome and aboral trochal band, and 9–13 between aboral trochal band and scopula. Pseudovorticella spathulata sp. n. differs from its congeners by the following combination of characters: elongate‐elliptical cell; a single contractile vacuole near ventral wall of infundibulum; a J‐shaped macronucleus; P3 three‐rowed; 24–34 silverlines between oral area and aboral trochal band and 6–10 between aboral trochal band and scopula. Pseudovorticella qinghaiensis sp. n. is characterized by: cell with an oval outline; a single contractile vacuole near ventral wall of infundibulum; a C‐shaped macronucleus; P3 three‐rowed; 30–35 and 9–11 transverse silverlines above and below the trochal band, respectively. The SSU rDNA sequences of five Pseudovorticella species, namely P. annulata, P. monilata, P. parakenti, P. spathulata sp. n., and P. cf. vestita, plus that of Zoothamnium hartwigi, are reported for the first time and their evolutionary relationships are investigated. Five undefined Pseudovorticella forms are considered might be conspecific with P. monilata. Two congeners are conspecific with P. spathulata sp. n. Phylogenetic analyses based on SSU rDNA sequences reveal that Pseudovorticella is not monophyletic and Z. hartwigi clusters with its congeners as expected.     

Competitive interactions between two allelopathic algal species: Heterosigma akashiwo and Phaeodactylum tricornutum

ABSTRACT

Both Heterosigma akashiwo and Phaeodactylum tricornutum have been reported to produce allelochemicals capable of inhibiting the growth of co-occurring microalgae. Here, potential allelopathy between H. akashiwo and P. tricornutum was evaluated using bi-algal culture, cell-free culture filtrate and a no-contact co-culturing system in nutrient-replete media. Experiments were also conducted in the no-contact co-culturing system under nutrient-limited conditions. In nutrient-replete bi-algal culture, the growth of P. tricornutum and H. akashiwo each tended to be strongly suppressed when the other species was inoculated at high cell densities. A mathematical model was used to simulate the growth interactions of the two species in bi-algal culture and showed that P. tricornutum outcompeted H. akashiwo over time with different initial cell densities under nutrient-sufficient conditions, indicating that P. tricornutum was more potent in allelopathy. Heterosigma akashiwo growth was inhibited both in the P. tricornutum culture filtrate and no-contact co-culturing system. This confirmed that the extracellular allelopathic compounds released by P. tricornutum were one of the sources of the H. akashiwo growth inhibition. Nutrient deficiency did not increase the extent of allelopathic activity of allelochemicals.     

Integrative taxonomy of the Rhinolophus macrotis complex (Chiroptera,Rhinolophidae) in Vietnam and nearby regions

The taxonomic status of Rhinolophus macrotis sensu lato (s.l.) in Vietnam and adjacent territories remains problematic. To address this issue, we performed an integrated study of morphological, acoustic, and genetic characters of R. macrotis s.l. specimens and compared these with sympatric species within the philippinensis group (R. marshalli, R. paradoxolophus, and R. rex). Our results reveal that in addition to a cryptic species of R. macrotis previously found in Jiangxi and Jingmen, China, R. macrotis s.l. in continental Asia includes three further species, namely R. cf. siamensis, R. cf. macrotis, and R. cf. macrotis “Phia Oac.” These four taxa are distinguished from genuine R. macrotis in Nepal and R. siamensis in Thailand by their morphological and/or genetic features. Further taxonomic evaluation of the subspecies of R. macrotis s.l. is needed to determine their affinities with recently recognized cryptic species and to possibly describe new taxa. Our results also show that interspecific divergences in mitochondrial DNA sequences (Cytb and COI genes) among taxa within the philippinensis group (particularly between R. cf. siamensis/R. cf. macrotis and R. rex/R. paradoxolophus) are significantly lower than those of other morphological groups in the genus. These phylogenetic patterns might be explained by recent allopatric speciation or ancient introgression events among ancestors of the taxa during the Pleistocene. However, further investigations including genetic analyses of nuclear genes are needed to test the latter hypothesis.     

Survival strategy of the endangered tree Acer catalpifolium Rehd., based on 13C fractionation

We conducted a field investigation and evaluation of ¹³C natural abundance to determine the growth habit and propagation strategy of Acer catalpifolium Rehd., a tree species native to China that is highly endangered. The results showed that A. catalpifolium is a K‐selected strategist and pioneer species. Its narrow ecological range limits its geographical distribution, and poor fecundity limits its population size. The analysis of ¹³C natural abundance showed that A. catalpifolium does not use organic matter for reproduction when its stand volume is less than 1.08 × 10⁶ cm³ or it is less than 18.6 m tall, but it does use this strategy when it has a sufficient 1.08 × 10⁶ cm³ stand volume or more or is taller than 18.6 m. If environmental conditions are not conducive (e.g., severe human disturbance, cliff edges, or fierce interspecific competition) to the continued growth of the tree, A. catalpifolium may allocate organic matter for reproduction. Human disturbance seems to promote the population expansion of A. catalpifolium. We provide our suggestions for the promotion and protection of A. catalpifolium as a species.     

Hybridization and introgression among three Aconitum (Ranunculaceae) species of different ploidy levels in the Tatra Mountains (Western Carpathians)

Hybridization among species of A conitum effects their morphology and ecology. In this study the hybridization between the diploid 2n(2x) = 16 ( A . lasiocarpum and A . variegatum) and tetraploid 2n(4x) = 32 ( A . firmum) species was documented in the Tatra Mountains (Western Carpathians) in a small, local population in a semi‐natural site. The hybrid species were: homoploid A . × pawlowskii ( A . lasiocarpum × A . variegatum), and triploid A . × berdaui ( A . firmum × A . variegatum, 2n(3x) = 24). Chloroplast DNA (cpDNA) alleles formed two distinct haplotypes, one typical for the tetraploid and another for diploid lines, shared between the tetraploid, triploid and diploid groups, indicating introgressive hybridization. The presumed gene flow was from the tetraploid to diploid species via the triploid bridge. The only two specimens of A . × pawlowskii that harbored tetraploid ( A . firmum) type cpDNA possessed bracteoles of A . firmum‐type. The remaining introgressed (cpDNA and Inter Simple Sequence Repeats (ISSR)) specimens ( A . variegatum) were morphologically pure, implying cryptic introgression. ISSR loci shared between the tetraploid A . firmum and diploid A . variegatum support the hypothesis of an ancient allopolyploid origin of A . firmum and the diploid species of A . variegatum‐type as one of its parent.     

A polyphasic approach to the delimitation of diatom species: a case study for the genus Pinnularia (Bacillariophyta)

Diatoms are one of the most abundant and arguably the most species‐rich group of protists. Diatom species delimitation has often been based exclusively on the recognition of morphological discontinuities without investigation of other lines of evidence. Even though DNA sequences and reproductive experiments have revealed several examples of (pseudo)cryptic diversity, our understanding of diatom species boundaries and diversity remains limited. The cosmopolitan pennate raphid diatom genus Pinnularia represents one of the most taxon‐rich diatom genera. In this study, we focused on the delimitation of species in one of the major clades of the genus, the Pinnularia subgibba group, based on 105 strains from a worldwide origin. We compared genetic distances between the sequences of seven molecular markers and selected the most variable pair, the mitochondrial cox1 and nuclear encoded LSU rDNA, to formulate a primary hypothesis on the species limits using three single‐locus automated species delimitation methods. We compared the DNA‐based primary hypotheses with morphology and with other available lines of evidence. The results indicate that our data set comprised 15 species of the P. subgibba group. The vast majority of these taxa have an uncertain taxonomic identity, suggesting that several may be unknown to science and/or members of (pseudo)cryptic species complexes within the P. subgibba group.     

Biodiversity of Klebsormidium (Streptophyta) from alpine biological soil crusts (Alps,Tyrol, Austria,and Italy)

Forty Klebsormidium strains isolated from soil crusts of mountain regions (Alps, 600–3,000 m elevation) were analyzed. The molecular phylogeny (internal transcribed spacer rDNA sequences) showed that these strains belong to clades B/C, D, E, and F. Seven main (K. flaccidum, K. elegans, K. crenulatum, K. dissectum, K. nitens, K. subtile, and K. fluitans) and four transitional morphotypes (K. cf. flaccidum, K. cf. nitens, K. cf. subtile, and K. cf. fluitans) were identified. Most strains belong to clade E, which includes isolates that prefer humid conditions. One representative of the xerophytic lineage (clade F) as well as few isolates characteristic of temperate conditions (clades B/C, D) were found. Most strains of clade E were isolated from low/middle elevations (<1,800 m above sea level; a.s.l.) in the pine‐forest zone. Strains of clades B/C, D, and F occurred sporadically at higher elevations (1,548–2,843 m a.s.l.), mostly under xerophytic conditions of alpine meadows. Comparison of the alpine Klebsormidium assemblage with data from other biogeographic regions indicated similarity with soil crusts/biofilms from terrestrial habitats in mixed forest in Western Europe, North America, and Asia, as well as walls of buildings in Western European cities. The alpine assemblage differed substantially from crusts from granite outcrops and sand dunes in Eastern Europe (Ukraine), and fundamentally from soil crusts in South African drylands. Epitypification of the known species K. flaccidum, K. crenulatum, K. subtile, K. nitens, K. dissectum, K. fluitans, K. mucosum, and K. elegans is proposed to establish taxonomic names and type material as an aid for practical studies on these algae, as well as for unambiguous identification of alpine strains. New combination Klebsormidium subtile (Kützing) Mikhailyuk, Glaser, Holzinger et Karsten comb. nov. is made.     

Contrasting effects of high‐intensity photosynthetically active radiation on two bloom‐forming dinoflagellates

While light limitation can inhibit bloom formation in dinoflagellates, the potential for high‐intensity photosynthetically active radiation (PAR) to inhibit blooms by causing stress or damage has not been well‐studied. We measured the effects of high‐intensity PAR on the bloom‐forming dinoflagellates Alexandrium fundyense and Heterocapsa rotundata. Various physiological parameters (photosynthetic efficiency F_v/F_m, cell permeability, dimethylsulfoniopropionate [DMSP], cell volume, and chlorophyll‐a content) were measured before and after exposure to high‐intensity natural sunlight in short‐term light stress experiments. In addition, photosynthesis‐irradiance (P‐E) responses were compared for cells grown at different light levels to assess the capacity for photophysiological acclimation in each species. Experiments revealed distinct species‐specific responses to high PAR. While high light decreased F_v/F_m in both species, A. fundyense showed little additional evidence of light stress in short‐term experiments, although increased membrane permeability and intracellular DMSP indicated a response to handling. P‐E responses further indicated a high light‐adapted species with Chl‐a inversely proportional to growth irradiance and no evidence of photoinhibition; reduced maximum per‐cell photosynthesis rates suggest a trade‐off between photoprotection and C fixation in high light‐acclimated cells. Heterocapsa rotundata cells, in contrast, swelled in response to high light and sometimes lysed in short‐term experiments, releasing DMSP. P‐E responses confirmed a low light‐adapted species with high photosynthetic efficiencies associated with trade‐offs in the form of substantial photoinhibition and a lack of plasticity in Chl‐a content. These contrasting responses illustrate that high light constrains dinoflagellate community composition through species‐specific stress effects, with consequences for bloom formation and ecological interactions within the plankton.     

Coexistence of two Cyclotella diatom species in the plankton of Lake Baikal

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Temperature × light interaction and tolerance of high water temperature in the planktonic freshwater flagellates Cryptomonas (Cryptophyceae) and Dinobryon (Chrysophyceae)

Using microcosm experiments, we investigated the interactive effects of temperature and light on specific growth rates of three species each of the phytoplanktonic genera Cryptomonas and Dinobryon. Several species of these genera play important roles in the food web of lakes and seem to be sensitive to high water temperature. We measured growth rates at three to four photon flux densities ranging from 10 to 240 μmol photon · m^?2 · s^?1 and at 4–5 temperatures ranging from 10°C to 28°C. The temperature × light interaction was generally strong, species specific, and also genus specific. Five of the six species studied tolerated 25°C when light availability was high; however, low light reduced tolerance of high temperatures. Growth rates of all six species were unaffected by temperature in the 10°C–15°C range at light levels ≤50 μmol photon · m^?2 · s^?1. At high light, growth rates of Cryptomonas spp. increased with temperature until the temperature optimum was reached and then declined. The Dinobryon species were less sensitive than Cryptomonas spp. to photon flux densities of 40 μmol photon · m^?2 · s^?1 and 200 μmol photon · m^?2 · s^?1 over the entire temperature range but did not grow under a combination of very low light (10 μmol photon · m^?2 · s^?1) and high temperature (≥20°C). Among the three Cryptomonas species, cell volume declined with temperature and the maximum temperature tolerated was negatively related to cell size. Since Cryptomonas is important food for microzooplankton, these trends may affect the pelagic carbon flow if lake warming continues.     

Comparative phylogeographic study of Hosta sieboldiana and Hosta albomarginata (Asparagaceae) in Japan

We analyzed variations in chloroplast DNA (cpDNA) in the widespread herbaceous species Hosta sieboldiana and Hosta albomarginata across large portions of their geographic ranges in the Japanese archipelago. Our objective was to compare the phylogeographic histories and phylogeographic structures of the two congeneric species in the Japanese archipelago. The location of the study is Japanese archipelago. We sequenced 1380 bp of noncoding cpDNA from 45 populations of H. sieboldiana (n = 362) and 55 populations of H. albomarginata (n = 436) to assess genetic variations within and among populations across almost the entire distributions of the species in Japan. Extant patterns of geographic structure were analyzed using statistical parsimony networks and spatial analysis of molecular variance (SAMOVA). We also used Monmonier's algorithm to detect genetic barriers between regions. Relationships between the populations were examined using a neighbor‐joining (NJ) method. Four haplotypes were found for H. sieboldiana, whereas eight haplotypes were identified for H. albomarginata. Total genetic haplotype diversity (hT) and within‐population haplotype diversity (hS) for H. sieboldiana were 0.352 and 0.040, respectively, while the values for H. albomarginata were 0.529 and 0.085, respectively. The population differentiations (GST) for H. sieboldiana and H. albomarginata were 0.839 and 0.886, respectively. The SAMOVA analysis revealed two clusters in H. sieboldiana and four clusters in H. albomarginata. Differentiations between and among the clusters were supported by the BARRIER analysis and the NJ tree. We detected differences in the population genetic structure between the two species. We found that H. sieboldiana had lower haplotype diversity than H. albomarginata. These results may be partially explained by the difference in ecological habitats and geographic distributions between the species. Hosta albomarginata is more widely distributed than H. sieboldiana in East Asia including Russia, and this large distribution range would enable more chances to intraspecific gene flow.