Basal Angiosperms Research Articles

How deep is the conflict between molecular and fossil evidence on the age of angiosperms?

The timing of the origin of angiosperms is a hotly debated topic in plant evolution. Molecular dating analyses that consistently retrieve pre-Cretaceous ages for crown-group angiosperms have eroded confidence in the fossil record, which indicates a radiation and possibly also origin in the Early Cretaceous. Here, we evaluate paleobotanical evidence on the age of the angiosperms, showing how fossils provide crucial data for clarifying the situation. Pollen floras document a Northern Gondwanan appearance of monosulcate angiosperms in the Valanginian and subsequent poleward spread of monosulcates and tricolpate eudicots, accelerating in the Albian. The sequence of pollen types agrees with molecular phylogenetic inferences on the course of pollen evolution, but it conflicts strongly with Triassic and early Jurassic molecular ages, and the discrepancy is difficult to explain by geographic or taphonomic biases. Critical scrutiny shows that supposed pre-Cretaceous angiosperms either represent other plant groups or lack features that might confidently assign them to the angiosperms. However, the record may allow the Late Jurassic existence of ecologically restricted angiosperms, like those seen in the basal ANITA grade. Finally, we examine recently recognized biases in molecular dating and argue that a thoughtful integration of fossil and molecular evidence could help resolve these conflicts.

The morphological relationship between carpels and ovules in angiosperms: pitfalls of morphological interpretation

Carpels and ovules have been differently interpreted over the past two centuries. In this review, some of these interpretations are highlighted, with particular emphasis on the current situation. Ovules are part of and are enclosed in carpels in all living angiosperms. Living angiosperms are monophyletic, and the evolutionary association between ovules and the leaf-like part, the carpel wall, had taken place at or before the time the clade of extant angiosperms was established. From what we know at present, there are no ‘cauline’ ovules in extant angiosperms. Developmentally, carpel walls and ovules are not always synchronous across all extant angiosperms. In early development ovules may be relatively precocious or relatively late compared with carpel walls. They are late in early-diverging angiosperms (ANITA grade, magnoliids, some early-diverging eudicots) but precocious in some more derived groups (e.g. some Caryophyllales and Primulaceae). Carpel primordia have a certain depth in the floral apex, and the entire activated area of a carpel primordium may be several cell layers thick. Thus, the carpel is ‘embedded’ or ‘rooted’ within the remaining floral apex. The parts of a carpel develop at different times in carpel ontogeny and probably evolved at different times on the line leading to the angiosperms, which needs to be considered in interpretations. Carpel development depends on a complex genetic network, which increased stepwise over evolutionary time and contains hundreds of genes revealed in molecular developmental biology. The evolutionary history of such networks in carpel walls and ovules is unlikely to be easily disentangled, as most of these genes are not transcription factors.

De novo assembly of Persea americana cv. \u2018Hass\u2019 transcriptome during fruit development

BackgroundAvocado (Persea americana Mill.) is a basal angiosperm from the Lauraceae family. This species has a diploid genome with an approximated size of ~ 920 Mbp and produces a climacteric, fleshy and oily fruit. The flowering and fruit set are particularly prolonged processes, lasting between one to three months, generating important differences in physiological ages of the fruit within the same tree. So far there is no detailed genomic information regarding this species, being the cultivar ‘Hass’ especially important for avocado growers worldwide. With the aim to explore the fruit avocado transcriptome and to identify candidate biomarkers to monitore fruit development, we carried out an RNA-Seq approach during 4 stages of ‘Hass’ fruit development: 150 days after fruit set (DAFS), 240 DAFS, 300 DAFS (harvest) and 390 DAFS (late-harvest).ResultsThe ‘Hass’ de novo transcriptome contains 62,203 contigs (x̅=988 bp, N50 = 1050 bp). We found approximately an 85 and 99% of complete ultra-conserved genes in eukaryote and plantae database using BUSCO (Benchmarking Universal Single-Copy Orthologs) and CEGMA (Core Eukaryotic Gene Mapping Approach), respectively. Annotation was performed with BLASTx, resulting in a 58% of annotated contigs (90% of differentially expressed genes were annotated). Differentially expressed genes analysis (DEG; with False Discovery Rate ≤ 0.01) found 8672 genes considering all developmental stages. From this analysis, genes were clustered according to their expression pattern and 1209 genes show correlation with the four developmental stages.ConclusionsCandidate genes are proposed as possible biomarkers for monitoring the development of the ‘Hass’ avocado fruit associated with lipid metabolism, ethylene signaling pathway, auxin signaling pathway, and components of the cell wall.

Transcriptomics of manually isolated Amborella trichopoda egg apparatus cells

Key messageA protocol for the isolation of egg apparatus cells from the basal angiosperm Amborella trichopoda to generate RNA-seq data for evolutionary studies of fertilization-associated genes.Sexual reproduction is particularly complex in flowering plants (angiosperms). Studies in eudicot and monocot model species have significantly contributed to our knowledge on cell fate specification of gametophytic cells and on the numerous cellular communication events necessary to deliver the two sperm cells into the embryo sac and to accomplish double fertilization. However, for a deeper understanding of the evolution of these processes, morphological, genomic and gene expression studies in extant basal angiosperms are inevitable. The basal angiosperm Amborella trichopoda is of special importance for evolutionary studies, as it is likely sister to all other living angiosperms. Here, we report about a method to isolate Amborella egg apparatus cells and on genome-wide gene expression profiles in these cells. Our transcriptomics data revealed Amborella-specific genes and genes conserved in eudicots and monocots. Gene products include secreted proteins, such as small cysteine-rich proteins previously reported to act as extracellular signaling molecules with important roles during double fertilization. The detection of transcripts encoding EGG CELL 1 (EC1) and related prolamin-like family proteins in Amborella egg cells demonstrates the potential of the generated data set to study conserved molecular mechanisms and the evolution of fertilization-related genes and their encoded proteins.

Scaling of phloem hydraulic resistance in stems and leaves of the understory angiosperm shrub Illicium parviflorum.

Recent studies in canopy-dominant trees revealed axial scaling of phloem structure. However, whether this pattern is found in woody plants of the understory, the environment of most angiosperms from the ANA grade (Amborellales-Nymphaeales-Austrobaileyales), is unknown. We used seedlings and adult plants of the understory tropical shrub Illicium parviflorum, a member of the lineage Austrobaileyales, to explore the anatomy and physiology of the phloem in their aerial parts, including changes through ontogeny. Adult plants maintain a similar proportion of phloem tissue across stem diameters, but larger conduit dimensions and number cause the hydraulic resistance of the phloem to decrease toward the base of the plant. Small sieve plate pores resulted in an overall higher sieve tube hydraulic resistance than has been reported in other woody angiosperms. Sieve elements increase in size from minor to major leaf veins, but were shorter and narrower in petioles. The low carbon assimilation rates of seedlings and mature plants contrasted with a 3-fold higher phloem sap velocity in seedlings, suggesting that phloem transport velocity is modulated through ontogeny. The overall architecture of the phloem tissue in this understory angiosperm shrub scales in a manner consistent with taller trees that make up the forest canopy. Thus, the evolution of larger sieve plate pores in canopy-dominant trees may have played a key role in allowing woody angiosperms to extend beyond their understory origins.

Wood evolution: Baileyan trends and Functional traits in the fossil record

ABSTRACTWe revisited questions about changes in the incidences of functional wood anatomical traits through geologic time and compared the incidences of these traits in the fossil record with modern wood anatomical diversity patterns in order to test classical (“Baileyan”) and more recent ecophyletic hypotheses of xylem evolution. We contrast patterns through time for tropical and higher (paleo)latitudes. Data are from the InsideWood database. There are striking differences between woods from high and mid latitudes versus tropical (paleo)-latitudes. At temperate and subtropical latitudes (Laurasia and high latitude Gondwana), the epoch by epoch time series supports the Baileyan transformation series of vessel-bearing woody angiosperms (basal woody angiosperms and eudicots): “primitive” features such as scalariform perforations, exclusively solitary vessels, apotracheal diffuse parenchyma and heterocellular rays abound in the Cretaceous and become much less frequent in the Cenozoic, especially post-Eocene. In contrast, in the paleotropics hardly any changes occur in the incidences – each epoch has an equally “modern” spectrum of wood anatomical attributes. Although climatic gradients from the poles to the equator were less steep in the Cretaceous than in the late Cenozoic, the wood anatomical differences between mid-high latitude woods and tropical woods were much more pronounced in the Cretaceous than in later epochs. This seeming paradox is discussed but we cannot resolve it.We suggest that tropical conditions have accelerated xylem evolution towards greater hydraulic efficiency (simple perforations), biological defense and hydraulic repair (elaborate paratracheal parenchyma patterns) as evidenced by late Cretaceous tropical latitude woods having near modern incidences of almost all traits. At higher paleolatitudes of both the Northern and Southern Hemisphere “ancestral” features such as scalariform perforations were retained in cooler and frost-prone regions where they were not selected against in mesic habitats because of lower demands on conductive efficiency, and could even be advantageous in trapping freeze-thaw embolisms. The fossil wood record remains too incomplete for testing hypotheses on the wood anatomy of the earliest angiosperms. The low incidence of so-called “xerophobic” woods sensu Feild with scalariform perforations with numerous (over 40) closely spaced bars in the Cretaceous tropical fossil record is puzzling. At higher paleolatitudes such woods are common in the Cretaceous.Ring porosity, an indicator of seasonal climates and deciduousness, occurs at low levels in the Cretaceous and Paleogene at higher paleolatitudes only, and reaches modern levels in the Miocene. In Neogene and Recent temperate Northern Hemisphere, wide vessels are virtually restricted to ring-porous woods. In the tropics, there is a low incidence of ring porosity throughout all epochs.The fossil record indicates that ecophysiological adaptation to tropical or temperate conditions was already evident in the Cretaceous with considerable latitudinal differences.

The complete chloroplast genome sequence of Myristica yunnanensis (Myristicaceae)

Myristica yunnanensis is a member of Myristicaceae. The M. yunnanensis chloroplast genome is found to be 155,923 bp in length and has a base composition of A (30.04%), G (19.28%), C (19.91%), and T (30.77%). The genome contained two short inverted repeat (IRa and IRb) regions (48,004 bp) which were separated by a large single-copy (LSC) region (87,088 bp) and a small single-copy (SSC) region (20,731 bp). The genome encodes 120 unique genes, including 85 protein-coding genes, 27 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Further, complete chloroplast sequence of M. yunnanensis was aligned together with Horsfieldia pandurifolia and other Magnoliales and basal angiosperms species which have reported the complete chloroplast sequence. This complete chloroplast genome will provide valuable information for the development of DNA markers for future species resource development and phylogenetic analysis of M. yunnanensis.

Biogeografía de la sección Cymbostemon (Illicium, Schisandraceae) en el Nuevo Mundo

Illicium es un genero de la familia Schisandraceae (Angiospermas Basales), nativo del Sudeste Asiatico, del viejo mundo, las Indias Occidentales, el Caribe Mexicano y el sudeste de Estados Unidos, en el Nuevo Mundo. La dispersion balistica de sus semillas y su presencia en bosques nublados y zonas templadas en occidente, sugieren que su distribucion disjunta es producto de procesos de vicarianza y no de dispersion a larga distancia. Se presenta un repaso de la biologia, ecologia y biogeografia del genero en el Nuevo Mundo.

Recent advances in New Caledonian biogeography.

The biota of New Caledonia is one of the most unusual in the world. It displays high diversity and endemism, many peculiar absences, and far-flung biogeographic affinities. For example, New Caledonia is the only place on Earth with both main clades of flowering plants - the endemic Amborella and 'all the rest', and it also has the highest concentration of diversity in conifers. The discovery of Amborella's phylogenetic position led to a surge of interest in New Caledonian biogeography, and new studies are appearing at a rapid rate. This paper reviews work on the topic (mainly molecular studies) published since 2013. One current debate is focused on whether any biota survived the marine transgressions of the Paleocene and Eocene. Total submersion would imply that the entire fauna was derived by long-distance dispersal from continental areas since the Eocene, but only if no other islands (now submerged) were emergent. A review of the literature suggests there is little actual evidence in geology for complete submersion. An alternative explanation for New Caledonia's diversity is that the archipelago acted as a refugium, and that the biota avoided the extinctions that occurred in Australia. However, this is contradicted by the many groups that are anomalously absent or depauperate in New Caledonia, although represented there by a sister group. The anomalous absences, together with the unusual levels of endemism, can both be explained by vicariance at breaks in and around New Caledonia. New Caledonia has always been situated at or near a plate boundary, and its complex geological history includes the addition of new terranes (by accretion), orogeny, and rifting. New Caledonia comprises 'basement' terranes that were part of Gondwana, as well as island arc and forearc terranes that accreted to the basement after it separated from Gondwana. The regional tectonic history helps explain the regional biogeography, as well as distribution patterns within New Caledonia. These include endemics on the basement terranes (for example, the basal angiosperm, Amborella), disjunctions at the West Caledonian fault zone, and great biotic differences between Grande Terre and the Loyalty Islands.

Intergeneric Relationships within the Early-Diverging Angiosperm Family Nymphaeaceae Based on Chloroplast Phylogenomics.

The order Nymphaeales, consisting of three families with a record of eight genera, has gained significant interest from botanists, probably due to its position as a basal angiosperm. The phylogenetic relationships within the order have been well studied; however, a few controversial nodes still remain in the Nymphaeaceae. The position of the Nuphar genus and the monophyly of the Nymphaeaceae family remain uncertain. This study adds to the increasing number of the completely sequenced plastid genomes of the Nymphaeales and applies a large chloroplast gene data set in reconstructing the intergeneric relationships within the Nymphaeaceae. Five complete chloroplast genomes were newly generated, including a first for the monotypic Euryale genus. Using a set of 66 protein-coding genes from the chloroplast genomes of 17 taxa, the phylogenetic position of Nuphar was determined and a monophyletic Nymphaeaceae family was obtained with convincing statistical support from both partitioned and unpartitioned data schemes. Although genomic comparative analyses revealed a high degree of synteny among the chloroplast genomes of the ancient angiosperms, key minor variations were evident, particularly in the contraction/expansion of the inverted-repeat regions and in RNA-editing events. Genome structure, and gene content and arrangement were highly conserved among the chloroplast genomes. The intergeneric relationships defined in this study are congruent with those inferred using morphological data.

Aquacultural, Nutritional and Therapeutic Biology of Delicious Seeds of Euryale ferox Salisb. : A Minireview.

Euryale ferox Salisb. (Makhana) is a rooted macro-hydrophyte, grown as a crop in north Bihar wetlands, India. Makhana refers to yummy pops prepared through mechanical smacking of the baked seeds of E. ferox. New techniques have been evolved to produce pops from seeds at a brisk pace. It is specially associated with marital rituals possibly in view of its spermatogenic properties. It has a high amino acid index but a low glycemic value. The plant carries medicinal values against cardiovascular and diabetes-related diseases. Makhana pops with a high volume to mass ratio, is developed as a reliable system for drug delivery in the recent times. There is a fair prospect of raising multi-faceted industry based on Makhana culture, harvest, post-harvest safety, preparation of pops and various types of food products therefrom and marketing in areas where water-logging is considered as a curse. It may generate employment and strengthen regional economy propping check on population migration primarily due to non-employment and poverty. Active research is required to harness this macro-hydrophyte along with co-culture of compatible fish varieties and other hydrophytes into a sustainable livelihood and economic prosperity.

Nectary ultrastructure of Cabomba caroliniana Gray (Cabombaceae)

Cabomba Aubl. is a genus considered as a potential genetic model for studies of early angiosperm evolution, accordingly, it is important to expand the knowledge of it. This paper reports the study of the anatomy and the ultrastructure of the nectary of Cabomba caroliniana Gray using bright-field microscope, scanning and transmission electron microscope in order to understand its secretion mechanism. C. caroliniana has protoginous flowers and the anthesis lasts two days. Nectaries of C. caroliniana are located in two basal lobes or yellow auricles of each white petal. Most nectar is observed in the area above the pronounced auricles. The secretion is released mainly by the four-cellular trichomes or hydropotens present in both nectary epidermis. The cellular ultrastructure indicates that the nectary is active during the two days of the anthesis. This agrees with the fact that in both anthesis days the fertile structures of the flower (first the stigmata and then the anthers) are disposed above the nectaries. The nectar secretion mechanism is discussed in relation to the present knowledge. The results of this study are related to what has been described for other basal angiosperms.

The complete mitochondrial genome of Schisandra sphenanthera (Schisandraceae)

Schisandra sphenanthera (Austrobaileyales) is a famous traditional Chinese medicine being long-history used, is also one of early-diverging angiosperms and important links to uncover the early evolution of angiosperms. Here the complete mitochondrial genome of S. sphenanthera was obtained for the first time. It is 1,106,521 bp in length with 46.4% GC content. It contains 58 genes, including 41 protein coding genes, three ribosomal RNA genes and 14 transfer RNA genes. Phylogenetic analysis indicated that S. sphenanthera was placed in the basal angiosperm just after Amborella and Nuphar. The mitogenome of S. sphenanthera would provide a reliable genetic and evolutionary resource.

Formation pattern in five types of pollen tetrad in Pseuduvaria trimera (Annonaceae).

In basal angiosperms, there are several types of permanent tetrad but their formation pattern remains elusive. Pseuduvaria trimera has five types of tetrads and is the species with the most abundant tetrad types in Annonaceae. In order to interpret the formation pattern of different tetrad types, pollen development was investigated from the microspore mother cell stage to the bicellular pollen stage and the ultrastructure of pollen wall in the five tetrad types using light microscopy, transmission electron microscopy, and confocal laser scanning microscopy. Both successive and intermediate cytokinesis were observed within the same anther. The nucleus location of the microspores together with cytokinesis determine the number and the spatial arrangement of callose plates, and further have an effect on the tetrad types. The anthers with or without septation and the arrangement of microsporocytes might be also related to the tetrad type. The individual pollen grains within the tetrads are connected with each other by crosswall cohesion and cytoplasmic channels at localized points in the proximal walls. The various types of tetrads, cytokinesis, and cohesion in P. trimera reflect the high diversity in pollen development, which enhances the dramatic variety in pollen morphology in this family. Our observations of the development of tetrads provided some new insights for interpreting the factors influencing the types of tetrads, and reported the existence of a cytoplasmic channel in Annonaceae for the first time.

Genome-wide identification and analysis of MICU genes in land plants and their potential role in calcium stress

Mitochondrial calcium uptake (MICU) plays a vital role in the regulation of mitochondrial calcium homeostasis, and, consequently, influences calcium signaling transduction. Although genes involved in mitochondrial calcium uptake have been well studied in animals, less is known about their ubiquity and function in plants. In this study, we identified 96 MICU genes in land plants. On the basis of phylogenetic analysis of MICU proteins, they were classified into three clades: MICU from eudicots (Clade I), from monocots (Clade II), and from a basal angiosperm, a bryophyte, and a lycophyte (Clade III). Pairwise identity analysis across all MICU proteins showed that they are highly conserved among land plants at the protein level. Conserved motif analysis showed that most MICU proteins contained three EF-hands, and an additional EF-hand motif first identified in the MICU of Arabidopsis thaliana but not mammals was found in all 96 putative MICU proteins. This suggests that a cellular pathway of calcium uptake and signaling that requires three EF-hand motifs is evolutionarily conserved in plants. In addition, we discovered that MICU-defective mutants of Arabidopsis thaliana exhibited longer roots than wild-type under high calcium stress. Concurrently, the mRNA transcription levels of MICU were decreased under high calcium conditions. These results suggest that loss-of-function mutations of MICU may have potential roles in helping plants resist high calcium stress. This study provides clues to the possible role of plant MICU in mitochondrial calcium uptake, as well as useful information to support further studies on MICU function in plants.

Functional diversification of Arabidopsis SEC1-related SM proteins in cytokinetic and secretory membrane fusion

Sec1/Munc18 (SM) proteins contribute to membrane fusion by interacting with Qa-SNAREs or nascent trans-SNARE complexes. Gymnosperms and the basal angiosperm Amborella have only a single SEC1 gene related to the KEULE gene in Arabidopsis However, the genomes of most angiosperms including Arabidopsis encode three SEC1-related SM proteins of which only KEULE has been functionally characterized as interacting with the cytokinesis-specific Qa-SNARE KNOLLE during cell-plate formation. Here we analyze the closest paralog of KEULE named SEC1B. In contrast to the cytokinesis defects of keule mutants, sec1b mutants are homozygous viable. However, the keule sec1b double mutant was nearly gametophytically lethal, displaying collapsed pollen grains, which suggests substantial overlap between SEC1B and KEULE functions in secretion-dependent growth. SEC1B had a strong preference for interaction with the evolutionarily ancient Qa-SNARE SYP132 involved in secretion and cytokinesis, whereas KEULE interacted with both KNOLLE and SYP132. This differential interaction with Qa-SNAREs is likely conferred by domains 1 and 2a of the two SM proteins. Comparative analysis of all four possible combinations of the relevant SEC1 Qa-SNARE double mutants revealed that in cytokinesis, the interaction of SEC1B with KNOLLE plays no role, whereas the interaction of KEULE with KNOLLE is prevalent and functionally as important as the interactions of both SEC1B and KEU with SYP132 together. Our results suggest that functional diversification of the two SEC1-related SM proteins during angiosperm evolution resulted in enhanced interaction of SEC1B with Qa-SNARE SYP132, and thus a predominant role of SEC1B in secretion.

Allocation of the epidermis to stomata relates to stomatal physiological control: Stomatal factors involved in the evolutionary diversification of the angiosperms and development of amphistomaty

The proportion of the leaf epidermis allocated to stomata (EP%) and stomatal function (the capacity to adjust stomatal pore area to regulate stomatal conductance: Gs) are key components in leaf gas exchange, and have likely played a major role in plant evolution. We examined the velocity of change in Gs (Gs50%) during a transition from steady state conditions in the light to darkness and EP% in 31 vascular plants with diverse evolutionary origins. Across all species, EP% correlated to Gs50% and the magnitude of Gs reduction (GsLIGHT-GsDARK) after the cessation of illumination. Those species with higher absolute and relative Gs50% values tended to distribute stomata more evenly over the abaxial and adaxial leaf surfaces, whereas species with lower Gs50% utilised only one leaf surface for gas exchange. Groups that diverged at relatively early stages in plant phylogeny, including ferns, gymnosperms and basal angiosperms, exhibited lower EP% and Gs50%, and took longer to achieve the initial 50% reduction in Gs (T50%) than the more recently diverging angiosperms; in particular, the amphistomatous monocot grasses, which also showed higher absolute rates of photosynthesis and Gs. We propose that selective pressures induced by declining [CO2] over the past 100 Myr have favoured greater allocation of the epidermis to stomata, increased amphistomaty (the presence of stomata on the abaxial and adaxial surfaces) and faster control of Gs in the more recently derived angiosperm groups. Modification of photosynthesis to enhance the carbon and water use efficiencies of C3 crops may therefore require concurrent increases in stomatal density and in the capacity of stomata to react quickly to environmental pressures.

Floral development of petaloid Alismatales as an insight into the origin of the trimerous Bauplan in monocot flowers.

Monocots are remarkably homogeneous in sharing a common trimerous pentacyclic floral Bauplan. A major factor affecting monocot evolution is the unique origin of the clade from basal angiosperms. The origin of the floral Bauplan of monocots remains controversial, as no immediate sister groups with similar structure can be identified among basal angiosperms, and there are several possibilities for an ancestral floral structure, including more complex flowers with higher stamen and carpel numbers, or strongly reduced flowers. Additionally, a stable Bauplan is only established beyond the divergence of Alismatales. Here, we observed the floral development of five members of the three 'petaloid' Alismatales families Butomaceae, Hydrocharitaceae, and Alismataceae. Outer stamen pairs can be recognized in mature flowers of Alismataceae and Butomaceae. Paired stamens always arise independently, and are either shifted opposite the sepals or close to the petals. The position of stamen pairs is related to the early development of the petals. In Butomaceae, the perianth is not differentiated and the development of the inner tepals is not delayed; the larger inner tepals (petals) only permit the initiation of stamens in antesepalous pairs. Alismataceae has delayed petals and the stamens are shifted close to the petals, leading to an association of stamen pairs with petals in so-called stamen-petal complexes. In the studied Hydrocharitaceae species, which have the monocot floral Bauplan, paired stamens are replaced by larger single stamens and the petals are not delayed. These results indicate that the origin of the floral Bauplan, at least in petaloid Alismatales, is closely linked to the position of stamen pairs and the rate of petal development. Although the petaloid Alismatales are not immediately at the base of monocot divergence, the floral evolution inferred from the results should be a key to elucidate the origin of the floral Bauplan of monocots.

Floral Biology and Embryological Studies are Important for Conservation of Threatened Plants Having Reproductive Bottlenecks:A Case Study of <i>Illicium griffithii</i> Hook. f. & Thomson

Information on reproductive biology of threatened plant species could be useful for conservation, particularly when the species fails to perpetuate in nature due to regeneration failure. In flowering plants, the domain of reproductive biology includes structural details of reproductive units such as flower or inflorescence, formation of viable gametes, pollination dynamics, role of pollinators, pollen–pistil interactions as determined through compatibility, breeding system and mating strategies, fertilization and embryogeny, seed development, dispersal and germination. The importance of reproductive biology in species conservation has been demonstrated through a case study of Illicium griffithii Hook f. & Thomson, a threatened plant species from Arunachal Pradesh. I. griffithii (Illiciaceae) is a member of the ANITA clade and a representative taxon of the three most basal angiosperms. The flowers of I. griffithii are obligate xenogamous, and hence compatible pollen grains only germinate on the stigmatic papillae. Esterase and phosphatase enzymatic activities are absent in most stigmatic surfaces. Therefore, stigmatic receptivity is absent in many carpels. The ovules are anatropous and bitegmic with a four-celled/four-nucleate structure of embryo sac at maturity. Antipodals and filiform apparatus are absent. Presence of mucilage cells in the embryo sac facilitates the entry of pollen tubes into it. Embryolike organization of the endosperm is present, with one pole globular having smaller cells and the other pole roughly filamentous with larger cells resembling that of a suspensor. Extragynoecial compitum is not observed in I. griffithii . The flowers are brooding sites for the midges and the young ovules are eaten by larvae of the midges. Only 10% of the flowers mature into 13-seeded fruits and the carpels of the remaining 90% of the flowers have seeds ranging from 1 to 5. The seedling survival rate is only 7%. In addition to the above-mentioned reproductive bottlenecks, the species is also being over-harvested. It is now categorized as endangered. The findings of the present study on reproductive biology of I. griffithii should help in improving its conservation status.

The largest early-diverging angiosperm family is mostly pollinated by ovipositing insects and so are most surviving lineages of early angiosperms.

Insect pollination in basal angiosperms is assumed to mostly involve 'generalized' insects looking for food, but direct observations of ANITA grade (283 species) pollinators are sparse. We present new data for numerous Schisandraceae, the largest ANITA family, from fieldwork, nocturnal filming, electron microscopy, barcoding and molecular clocks to infer pollinator/plant interactions over multiple years at sites throughout China to test the extent of pollinator specificity. Schisandraceae are pollinated by nocturnal gall midges that lay eggs in the flowers and whose larvae then feed on floral exudates. At least three Schisandraceae have shifted to beetle pollination. Pollination by a single midge species predominates, but one species was pollinated by different species at three locations and one by two at the same location. Based on molecular clocks, gall midges and Schisandraceae may have interacted since at least the Early Miocene. Combining these findings with a review of all published ANITA pollination data shows that ovipositing flies are the most common pollinators of living representatives of the ANITA grade. Compared to food reward-based pollination, oviposition-based systems are less wasteful of plant gametes because (i) none are eaten and (ii) female insects with herbivorous larvae reliably visit conspecific flowers.