Dissecting evolutionary dynamics of ecologically important traits is a long-term challenge for biologists. Attempts to understand natural variation and molecular mechanisms have motivated a move from laboratory model systems to non-model systems in diverse natural environments. Next generation sequencing methods, along with an expansion of genomic resources and tools, have fostered new links between diverse disciplines, including molecular biology, evolution, and ecology, and genomics. Great progress has been made in a few non-model wild plants, such as Arabidopsis relatives, monkey flowers, and wild sunflowers. Until recently, the lack of comprehensive genomic information has limited evolutionary and ecological studies to larger QTL regions rather than single gene resolution, and has hindered recognition of general patterns of natural variation and local adaptation. Further efforts in accumulating genomic data and developing bioinformatic and biostatistical tools are now poised to move this field forward. Integrative national and international collaborations and research communities are needed to facilitate development in the field of evolutionary and ecological genomics.
Abstract Beta diversity is the change in species composition among areas in a geographic region. The proportion of species shared between two areas often decreases when the distance separating them increases, leading to an increase in beta diversity. This study compares beta diversity among four classes of terrestrial vertebrates (mammals, birds, reptiles, and amphibians) at both regional (biogeographic realm) and global extents, using the same sets of faunal sample units for all four groups in each comparison. Beta diversity is lower for the two endothermic taxa (birds and mammals) than for the two ectothermic taxa (reptiles and amphibians) in all six biogeographic realms examined. When the four taxa in the six biogeographic realms are combined, beta diversity at the species rank is higher than that of the genus rank by a factor of 1.24, and is higher than that of the family rank by a factor of 1.85. The ratio of beta diversity at the genus rank to that at the family rank is 1.50. Beta diversity is slightly higher for ecoregions of 5000–99,999 km2 than for ecoregions of 100,000–5,000,000 km2.
Abstract New inference techniques, such as supertrees, have improved the construction of large phylogenies, helping to reveal the tree of life. In addition, these large phylogenies have enhanced the study of other evolutionary questions, such as whether traits have evolved in a neutral or adaptive way, or what factors have influenced diversification. However, supertrees usually lack branch lengths, which are necessary for all these issues to be investigated. Here, divergence times within the largest family of flowering plants, namely the Asteraceae, are reviewed to estimate time-calibrated branch lengths in the supertree of this lineage. An inconsistency between estimated dates of basal branching events and the earliest asteraceous fossil pollen record was detected. In addition, the impact of different methods of branch length assignment on the total number of transitions between states in the reconstruction of sexual system evolution in Asteraceae was investigated. At least for this dataset, different branch length assignation approaches influenced maximum likelihood (ML) reconstructions only and not Bayesian ones. Therefore, the selection of different branch length information is not arbitrary and should be carefully assessed, at least when ML approaches are being used. The reviewed divergence times and the estimated time-calibrated branch lengths provide a useful tool for future phylogenetic comparative and macroevolutionary studies of Asteraceae.
Abstract Adenophora is an extremely variable genus, and its taxonomy is very controversial. Of the genus, Adenophora potaninii complex, including A. potaninii, A. bockiana, A. wawreana, A. lobophylla, A. biformifolia, A. polydentata, and A. wawreana var. lanceifolia, is a typical group with different taxonomical treatments due to high level of morphological diversity. We carried out extensive biosystematic studies based on population sampling, transplantation experiments and offspring tests, cluster analysis, and a crossing experiment. The results reveal four main findings. (i) Leaf forms of the A. potaninii complex were extremely polymorphic; the leaf form of A. potaninii and A. bockiana, and that of A. wawreana and A. biformifolia could be found, respectively, on a single population or among the offsprings of a single plant. (ii) Cluster analysis and a crossing experiment indicated that A. bockiana and A. polydentata could not be separated from A. potaninii, nor A. biformifolia from A. wawreana. (iii) Adenophora potaninii and A. wawreana were gradational in morphology and their compatibility value was slightly reduced compared to that within each entity. (iv) Adenophora lobophylla was distinct from the other members of the complex in shape and size of corolla, relative length of style, and shape of capsule. This species was incompatible reproductively with the other members of the complex, but partly compatible with A. stenanthina, a species in another section. Therefore, we recognized only one species with two subspecies in the complex, A. potaninii subsp. potaninii and subsp. wawreana, moved A. lobophylla out of the complex, and reduced all the other names as new synonyms.
Abstract We propose a simple statistical approach for using Dispersal–Vicariance Analysis (DIVA) software to infer biogeographic histories without fully bifurcating trees. In this approach, ancestral ranges are first optimized for a sample of Bayesian trees. The probability P of an ancestral range r at a node is then calculated as where Y is a node, and F(rY) is the frequency of range r among all the optimal solutions resulting from DIVA optimization at node Y, t is one of n topologies optimized, and Pt is the probability of topology t. Node Y is a hypothesized ancestor shared by a specific crown lineage and the sister of that lineage “x”, where x may vary due to phylogenetic uncertainty (polytomies and nodes with posterior probability <100%). Using this method, the ancestral distribution at Y can be estimated to provide inference of the geographic origins of the specific crown group of interest. This approach takes into account phylogenetic uncertainty as well as uncertainty from DIVA optimization. It is an extension of the previously described method called Bayes-DIVA, which pairs Bayesian phylogenetic analysis with biogeographic analysis using DIVA. Further, we show that the probability P of an ancestral range at Y calculated using this method does not equate to pp*F(rY) on the Bayesian consensus tree when both variables are <100%, where pp is the posterior probability and F(rY) is the frequency of range r for the node containing the specific crown group. We tested our DIVA-Bayes approach using Aesculus L., which has major lineages unresolved as a polytomy. We inferred the most probable geographic origins of the five traditional sections of Aesculus and of Aesculus californica Nutt. and examined range subdivisions at parental nodes of these lineages. Additionally, we used the DIVA-Bayes data from Aesculus to quantify the effects on biogeographic inference of including two wildcard fossil taxa in phylogenetic analysis. Our analysis resolved the geographic ranges of the parental nodes of the lineages of Aesculus with moderate to high probabilities. The probabilities were greater than those estimated using the simple calculation of pp*F(ry) at a statistically significant level for two of the six lineages. We also found that adding fossil wildcard taxa in phylogenetic analysis generally increased P for ancestral ranges including the fossil's distribution area. The ΔP was more dramatic for ranges that include the area of a wildcard fossil with a distribution area underrepresented among extant taxa. This indicates the importance of including fossils in biogeographic analysis. Exmination of range subdivision at the parental nodes revealed potential range evolution (extinction and dispersal events) along the stems of A. californica and sect. Parryana.
Abstract The fruit morphology of 18 taxa representing seven genera of the family Polygonaceae in West Africa was investigated using scanning electron microscopy. The achenes are trigonous, lenticular, globose, subglobose, heart shaped, ovoid, or cone like. Sizes range from 0.12 × 0.10 cm2 in Polygonum plebeium to 7.87 × 0.58 cm2 in Afrobrunnichia erecta. Colors are brown to black. The cells are isodiametric in P. plebeium, irregular in A. erecta, Antigonon leptopus, and Harpagocarpus snowdenii, and polygonal in other species. The walls are straight, curved, or undulate and are either raised or depressed. Afrobrunnichia erecta is characterized by deeply sinuate lateral walls. The cell surface may be smooth or tuberculate or fibrillate in the family, usually covered with wax deposits. The combination of these characters is mainly taxonomically useful at the tribal level and rarely at the specific or infraspecific level for the delimitation of the taxa.
Abstract It has been proposed that relative allocation to female function increases with plant size in animal-pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size-dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect-pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high-density population, 48% of ramets were male without female flowers, but in the low-density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal-pollinated plants, pointing towards further studies to test the hypothesis of size-dependent sex allocation using different allocation currencies.
Abstract Phytolacca is the biggest and most original genus in Phytolaccaceae and an important genus in plant systematic studies. Light microscopy results show that the Phytolacca americana L. ovule arises from the caulis (floral receptacle). The perisperm and hypostase are simultaneously initiated from the top several layers of cells of chalaza after fertilization, and the perisperm is located between the nucellus and hypostase. In the early stages of development, the hypostase cells are thin-walled with dense cytoplasm, clear nuclei, and some reserve granules. Later, at the heart-shaped embryo stage, the hypostase cells are dead and thick-walled. The main functions of the hypostase may be to maintain cellular division and perisperm growth without delivering nutrient materials to the perisperm. An evolutionary picture of placentation in Caryophyllales is also presented.
Abstract Recent years have witnessed a proliferation of quantitative methods for biogeographic inference. In particular, novel parametric approaches represent exciting new opportunities for the study of range evolution. Here, we review a selection of current methods for biogeographic analysis and discuss their respective properties. These methods include generalized parsimony approaches, weighted ancestral area analysis, dispersal–vicariance analysis, the dispersal–extinction–cladogenesis model and other maximum likelihood approaches, and Bayesian stochastic mapping of ancestral ranges, including a novel approach to inferring range evolution in the context of island biogeography. Some of these methods were developed specifically for problems of ancestral range reconstruction, whereas others were designed for more general problems of character state reconstruction and subsequently applied to the study of ancestral ranges. Methods for reconstructing ancestral history on a phylogenetic tree differ not only in the types of ancestral range states that are allowed, but also in the various historical events that may change the ancestral ranges. We explore how the form of allowed ancestral ranges and allowed transitions can both affect the outcome of ancestral range estimation. Finally, we mention some promising avenues for future work in the development of model-based approaches to biogeographic analysis.
Abstract Terminology of inflorescence diversity has often been used in a confusing way in the literature, partly because it was based on uncritical and outdated definitions. In particular, the terms cyme, thyrse, and panicle have been misused. Although a more critical classification worked out by several authors is available, it is unfortunately not in general use because most of the relevant publications are written in German. In addition, some terms have not been used in the same way by morphologists and developmental geneticists. The present review attempts to remedy the situation with a simple outline of a classification based on: (i) different branching patterns; (ii) differential elongation of axes of different orders; and (iii) repetition of basic ramification patterns in different ways. Racemose and cymose branching are two extreme patterns; the former with limitation of axial orders to two, the second with limitation of lateral axes of each order to two. In a branching system, a sequence of racemose → cymose and, within the cyme, of dichasial → monochasial is common, but the reverse sequence generally does not occur. Systematic and evolutionary aspects of inflorescences are briefly discussed. Branching patterns are often stable in larger clades. Inflorescences of mutants studied in developmental genetic studies are mainly altered in flower or branch numbers or relative branch length, but not in branching patterns. This is also a contribution towards the goal of a unified terminology for the different fields of biology dealing with inflorescences.
Abstract In the present study, the karyotypes of 34 populations belonging to 11 species and one variety of Heracleum from the Hengduan Mountains in China were examined. Chromosome numbers and the karyotypes of three species (H. souliei, H. kingdoni, and H. wenchuanense) are reported for the first time, as are the karyotypes of H. moellendorffii and H. henryi (tetraploid). Populations of H. candicans, H. franchetii, and H. kingdoni in the Hengduan Mountains were found to consist of a mixture of diploid and tetraploid plants. Except for four species of Heracleum, namely H. candicans, H. franchetii, H. henryi, and H. kingdoni, which have both diploid and tetraploid karyotypes, all other species of Heracleum are were found to be diploid. All karyotypes were found to belong to the 2A type of Stebbins, with the exception of H. candicans var. obtusifolium, which belongs to 2B, and H. hemsleyanum and H. franchetii (Mt. Dujuan, Daocheng, Sichuan, China), which belong to 1A. There was only a slight difference in the karyotype asymmetry index, which suggests a close kinship for species of Heracleum and that the entire phylogenetic development of Heracleum is relatively primitive. Species that exhibited advanced morphological features were also more advanced in karyotype structure, with the order of karyotype evolution being 1A→2A→2B. This phenomenon indicates that the species distributed in the Hengduan Mountains have not diverged completely and that the Hengduan Mountains are a relatively young and active area for the evolution of Heracleum. Polyploidization in Heracleum may be an important evolutionary mechanisms for some species, generating diversity. The biological attributes, distribution range, and the geological history of the genus have all played a part in accelerating the evolution through polyploidization or aneuploidization. It is known that as the distribution latitude of Heracleum decreases from north to south, the chromosome number, ploidy level, and asymmetry structure appear to increase. In the Hengduan Mountains, these tendencies are also evident. Finally, based on all the available cytogeographic data, we speculate that the more advanced tetraplont or aneuploid species of Heracleum in India may be derived from early diplont species that were distributed in the Caucasus region and Hengduan Mountains. The dispersal of Heracleum was from Eurasia to India, because this correlates with the emergence of the Himalayan Mountains through tectonic movement. Thus, the Hengduan Mountains are not only a center of diversity for Heracleum, but also a center of active speciation in modern times.
Abstract As one of the big genera in Apiaceae, Bupleurum L. has received considerable attention from plant taxonomists. Nevertheless, there are still many gaps in our knowledge of this genus, especially of those species endemic to China that have often been excluded from previous studies. In spite of a few recent studies on the phylogeny and classification of the Chinese Bupleurum, the most essential problem of species delimitation still remains unresolved. We re-evaluate the taxonomy of the Chinese Bupleurum using morphological and molecular evidence. Careful observations of living plants growing the field and herbarium specimens were made to understand the morphological variation and to ensure species identification for the molecular analysis. Phylogenetic analyses were carried out on sequence data of nuclear ribosomal internal transcribed spacer (nrITS), trnH-psbA, and matK, using parsimony and Bayesian approaches to evaluate species relationships. Analyses of both nrITS and combined datasets of the three regions revealed the following results: (i) the Chinese Bupleurum species were divided into two major lineages; and (ii) most species were well defined, but some traditional inter- and infraspecific relationships were not supported. Our results, along with the results of previous works support that the Chinese Bupleurum species were derived from two different lineages and should be placed in Neves and Watson's subgenus Bupleurum. Our detailed taxonomic re-assessment of several Chinese species resulted in new taxonomic recombinations with rank changes for three species: Bupleurum tenerum, B. amplexicaule, and B. franchetii; new combination for one variety, B. smithii var. flaviflorum; and the description of one variety and one species, B. stenophyllum var. leiocarpum and B. sikangense.
Abstract Gentianopsis paludosa (Hook. f.) Ma (Gentianaceae) is an important species in Tibetan folk medicine commonly used to clear away the “heat evils” and toxic materials. A survey of market samples revealed that nine adulterant species, Gentianopsis barbata, G. contorta, G. grandis, Halenia elliptica, Lomatogonium macranthum, L. rotatum, Swertia angustifolia, S. bifolia and S. erythrosticta, are often marketed as G. paludosa. Methods to distinguish G. paludosa from its adulterants are limited by current morphological and chemical methods. DNA sequence analysis of the nuclear ribosomal DNA internal transcribed spacer region (ITS) was used in the differentiation of G. paludosa from the adulterant species. The data showed that the internal transcribed spacer regions differ significantly between G. paludosa and all nine adulterant species, so that they could be easily distinguished at the DNA level.
Abstract Species of Prunus L. sect. Persica are not only important fruit trees, but also popular ornamental and medicinal plants. Correct identification of seedlings, barks, or fruit kernels is sometimes required, but no reliable morphological characters are available. Nowadays, the technique of DNA barcoding has the potential to meet such requirements. In this study, we evaluated the suitability of 11 DNA loci (atpB-rbcL, trnH-psbA, trnL-F, trnS-G, atpF-H, rbcL, matK, rpoB, rpoC1, nad1, and internal transcribed spacer [ITS]) as candidate DNA barcodes for peaches, using samples from 38 populations, covering all the species in sect. Persica. On the whole, the primers worked well in this group and sequencing difficulties were met only in the case of ITS locus. Five loci (rbcL, matK, rpoB, rpoC, and nad1) have very low variation rates, whereas atpB-rbcL, atpF-H, trnH-psbA, trnL-F and trnS-G show more variability. The most variable loci, atpB-rbcL and trnH-psbA, can distinguish three of the five species. Two two-locus combinations, atpB-rbcL+trnL-F and atpB-rbcL+atpF-H, can resolve all five species. We also find that identification powers of the loci are method-dependent. The NeighborNet method shows higher species identification power than maximum parsimony, neighbor joining, and unweighted pair group method with arithmetic mean methods.
Abstract Studies on the evolution of tropical taxa emphasize the role of vicariance and the break-up of Gondwana in explaining modern distributions. Earlier studies on figs (Ficus spp.) support this view. In the current study, we used an expanded sample (208 spp.) and improved molecular dating techniques to reconstruct the phylogenetic and biogeographic history of Ficus. Consistent with previous studies, our biogeographic analysis indicated that the ancestor of Ficus was present in Gondwana. However, a relaxed clock analysis relying on uncorrelated rates in BEAST suggested that the Neotropical section Pharmacosycea split-off in South America 86.67 Mya, and that other Ficus lineage ancestors originated in India. Most of the basal lineages appeared to have diverged following KT extinction, then rapidly diversified after India collided with continental Asia. The Afrotropical species most likely evolved initially in the Indian subcontinent then dispersed to Africa, either in the late Cretaceous of Madagascar or even later, following the Eocene collision of India with Asia. The Neotropical section Americana, either island-hopped to South America or took a northern route to the Americas through Europe prior to the terminal Eocene global cooling event. Ficus may have arrived in eastern Malesia following the collision of India with Asia, then widely dispersed thereafter. Given the wide ranges in our date estimates, several other scenarios are possible. However, contrary to earlier reports, our analyses suggest that vicariance played a relatively minor role compared with ecological opportunity and dispersal in the diversification of genus Ficus.
Abstract The origin of morphological and ecological novelties is a long-standing problem in evolutionary biology. Understanding these processes requires investigation from both the development and evolution standpoints, which promotes a new research field called “evolutionary developmental biology” (evo-devo). The fundamental mechanism for the origin of a novel structure may involve heterotopy, heterochrony, ectopic expression, or loss of an existing regulatory factor. Accordingly, the morphological and ecological traits controlled by the regulatory genes may be gained, lost, or regained during evolution. Floral morphological novelties, for example, include homeotic alterations (related to organ identity), symmetric diversity, and changes in the size and morphology of the floral organs. These gains and losses can potentially arise through modification of the existing regulatory networks. Here, we review current knowledge concerning the origin of novel floral structures, such as “evolutionary homeotic mutated flowers”, floral symmetry in various plant species, and inflated calyx syndrome (ICS) within Solanaceae. Functional evo-devo of the morphological novelties is a central theme of plant evolutionary biology. In addition, the discussion is extended to consider agronomic or domestication-related traits, including the type, size, and morphology of fruits (berries), within Solanaceae.
Abstract Microtropis macrocarpa C.Y. Cheng & T.C. Kao has been treated as a synonym of Microtropis macrophylla Merr. & Freeman in most taxonomic reports in China. According to our study, M. macrocarpa is an independent species endemic to Yunnan, China. Microtropis macrophylla and Microtropis pachyphylla Merr. & Freeman should be treated as synonyms of Microtropis longifolia Wall. ex Kurz. M. macrocarpa is also identified as a critically endangered species, CR B1ab (i,ii,iii,v), based on the IUCN Red List Categories and Criteria. The foliar surface, anther and pollen structures were also observed with a scanning electron microscope.
Abstract A universal method of molecular dating that can be applied to all families and genera regardless of their fossil records, or lack thereof, is highly desirable. A possible method for eudicots is to use a large phylogeny calibrated using deep fossils including tricolpate pollen as a fixed (124 mya) calibration point. This method was used to calculate node ages within three species-poor disjunct basal eudicot genera, Caulophyllum, Podophyllum and Pachysandra, and sensitivity of these ages to effects such as taxon sampling were then quantified. By deleting from one to three accessions related to each genus in 112 different combinations, a confidence range describing variation due only to taxon sampling was generated. Ranges for Caulophyllum, Podophyllum and Pachysandra were 8.4–10.6, 7.6–20.0, and 17.6–25.0 mya, respectively. However, the confidence ranges calculated using bootstrapping were much wider, at 3–19, 0–32 and 11–32 mya, respectively. Furthermore, deleting 10 adjacent taxa had a large effect in Pachysandra only, indicating that undersampling effects are significant among Buxales. Changes to sampling density in neighboring clades, or to the position of the fixed fossil calibration point had small to negligible effects. Non-parametric rate smoothing was more sensitive to taxon sampling effects than was penalized likelihood. The wide range for Podophyllum, compared to the other two genera, was probably due to a high degree of rate heterogeneity within this genus. Confidence ranges calculated by this method could be narrowed by sampling more individuals within the genus of interest, and by sequencing multiple DNA regions from all species in the phylogeny.
Abstract The karyomorphology of three species in Dipentodon (Dipentodontaceae), Perrottetia (Celastraceae), and Tapiscia (Tapisciaceae), namely Dipentodon sinicus, Perrottetia racemosa, and Tapiscia sinensis, was investigated in the present study. Recent molecular research has discovered close relationships among these three genera, which has led to the establishment of the order Huerteales with Perrottetia being placed in Dipentodontaceae. Herein we report the chromosome numbers of D. sinicus and P. racemosa for the first time, and present their karyotype formulas as 2n= 34 = 22 sm + 12 st (D. sinicus), 2n= 20 = 11 m + 9 sm (P. racemosa), and 2n= 30 = 22 m(2SAT) + 8sm (T. sinensis). Asymmetry of their karyotypes is categorized to be Type 3B in D. sinicus, Type 2A in P. racemosa, and Type 2A in T. sinensis. Each of the species shows special cytological features. Compared with Perrottetia, Dipentodon has a different basic chromosome number, a higher karyotype asymmetry, and different karyomorphology of its interphase nuclei, mitotic prophase, and metaphase. Thus, on the basis of these results, we have reservations regarding the suggestion of placing Dipentodon and Perrottetia together in the family Dipentodontaceae.
Glycosmis longipetala F. J. Mou & D. X. Zhang is described from Guangxi and Yunnan provinces in southwestern China. The new species is similar to G. cochinchinensis (Lour.) Pierre ex Engl. by its simple leaves, but distinguishable in having long-elliptic or oblanceolate (vs. ovate) leaves, long-ovoid to ellipsoid (vs. ovoid) floral buds, ovaries with many tubercles (vs. smooth) and glabrous (vs. pubescent) stamens. The pollen grains of the new species are 23.9±3.09 (20.8–27.0)×22.0±1.80 (20.4–24.4) μm in size with reticulate exine ornamentation in equatorial area and foveolate in polar area. The chromosome number of the new species is 2n=72.
Abstract Phylogeny and infrageneric relationships were reconstructed for Korean Viola (Violaceae) using eight chloroplast sequences: the atpB-rbcL intergenic spacer, the atpF-H intergenic spacer, the matK gene, the psbA-trnH intergenic spacer, the psbK-I intergenic spacer, the rpl16 intron, the rpoC1 exon 2, and the trnL-trnF regions. The combined analyses of the eight chloroplast regions suggest that sections Dischidium and Chamaemelanium are monophyletic, whereas section Nomimium is paraphyletic; sections Dischidium and Chamaemelanium form a clade with subsections Hypocarpae and Trigonocarpae of section Nomimium, but unresolved within the clade; two subsections (subsects. Bilobatae and Vaginatae) of section Nomimium form a clade and are placed between the stem and stemless species group; and subsection Patellares of section Nomimium is monophyletic, and Viola dissecta is diverged first in the clade with high support (BS = 100, PP = 100). Our present results support the subsectional grouping based on morphological characteristics, although discordance remained at the series level.
Abstract The pollen morphology of 11 species (including two subspecies and two varieties) belonging to two genera (Helianthemum and Fumana) of the family Cistaceae in Egypt was studied using light and scanning electron microscopy. Pollen grains of the studied taxa were found to be radially symmetrical and tricolporate. Pollen size, shape, apertures, and exine ornamentation characteristics were valuable parameters among the studied taxa. The largest pollen size was recorded in H. salicifolium and the smallest one observed in H. kahiricum subsp. schweinfurthii. Pollen shape in the Egyptian taxa varied from (sub-)prolate to prolate spheroidal, but F. arabica is different in having sub-oblate grains. The pollen data confirm that H. lippii and H. sessiliflorum are very closely related species. Pollen sculpture was useful in distinguishing between H. vesicarium var. vesicarium and H. vesicarium var. ciliatum. Three main pollen types of exine ornamentation were recognized: retipilate; reticulate to verrucate; and striate. Based on palynological data, a key for the studied taxa is suggested.
Abstract The pollen morphology of 13 taxa (34 specimens) of the genera Glechoma L., and Marmoritis Benth. was investigated in detail using light, scanning electron, and transmission electron microscopy. Pollen grains of all studied taxa are small to large in size (P= 32.5–60.4 μm, E= 20.2–50.5 μm), prolate-spheroidal to prolate in shape and mostly hexacolpate (the amb more or less circular or rarely ellipsoid) with granular membranes. The sexine ornamentation of Glechoma is bireticulate; the muri of the primary reticulum are irregularly circled, and lumen size is short. In contrast, the sexine surfaces of the Marmoritis pollen tend to more elongate or wider at the muri of the primary reticulum than those of the Glechoma. The pollen wall stratification of selected taxa (three from Glechoma and one from Marmoritis) is characterized by unbranched columellae, and continuous or distinctly discontinuous endexine based on transmission electron microscopy observation. The results of Glechoma and Marmoritis reveal rather similar pollen morphological features, however, fine details of sexine ornamentation are characteristic to differentiate the pollen taxa. Although these differences may be useful in establishing the taxonomic boundary between two genera, they are too weak to segregate diagnostic characters.
Abstract Embryophytes (land plants) are distinguished from their green algal ancestors by diplobiontic life cycles, that is, alternation of multicellular gametophytic and sporophytic generations. The bryophyte sporophyte is small and matrotrophic on the dominant gametophyte; extant vascular plants have an independent, dominant sporophyte and a reduced gametophyte. The elaboration of the diplobiontic life cycle in embryophytes has been thoroughly discussed within the context of the Antithetic and the Homologous Theories. The Antithetic Theory proposes a green algal ancestor with a gametophyte-dominant haplobiontic life cycle. The Homologous Theory suggests a green algal ancestor with alternation of isomorphic generations. The shifts that led from haplobiontic to diplobiontic life cycles and from gametophytic to sporophytic dominance are most probably related with terrestrial habitats. Cladistic studies strongly support the Antithetic Theory in repeatedly identifying charophycean green algae as the closest relatives of land plants. In recent years, exceptionally well-preserved axial gametophytes have been described from the Rhynie chert (Lower Devonian, 410 Ma), and the complete life cycle of several Rhynie chert plants has been reconstructed. All show an alternation of more or less isomorphic generations, which is currently accepted as the plesiomorphic condition among all early polysporangiophytes, including basal tracheophytes. Here we review the existing evidence for early embryophyte gametophytes. We also discuss some recently discovered plants preserved as compression fossils and interpreted as gametophytes. All the fossil evidence supports the Antithetic Theory and indicates that the gametophytic generation/sporophytic generation size and complexity ratios show a gradual decrease along the land plant phylogenetic tree.
Omphalogramma souliei Franch. is an endangered perennial herb only distributed in alpine areas of SW China. ISSR markers were applied to determine the genetic variation and genetic structure of 60 individuals of three populations of O. souliei in NW Yunnan, China. The genetic diversity at the species level is low with P=42.5% (percentage of polymorphic bands) and Hsp=0.1762 (total genetic diversity). However, a high level of genetic differentiation among populations was detected based on different measures (Nei's genetic diversity analysis: Gst=0.6038; AMOVA analysis: Fst=0.6797). Low level of genetic diversity within populations and significant genetic differentiation among populations might be due to the mixed mating system in which xenogamy predominated and autogamy played an assistant role in O. souliei. The genetic drift due to small population size and limited current gene flow also resulted in significant genetic differentiation. The assessment of genetic variation and differentiation of the endangered species provides important information for conservation on a genetic basis. Conservation strategies for this rare endemic species are proposed.
