Showing papers in "International Journal of Plant Sciences in 2012"
TL;DR: Evidence is presented to demonstrate that the evolutionary barrier to entry to the Cerrado is a weak one, presumably because of the ease of evolution of the necessary adaptations to fire regimes for lineages inhabiting neighboring fire-free biomes.
Abstract: A recent controversy concerns whether plant traits that are assumed to be adaptations to fire originally evolved in response to selective factors other than fire. We contribute to this debate by investigating the evolution of the endemic woody flora of the fire-prone Cerrado of central Brazil, the most species-rich savanna in the world. We review evidence from dated phylogenies and show that Cerrado lineages started to diversify less than 10 million years ago. These Cerrado lineages are characterized by fire-resistant traits such as thick, corky bark and root sprouting, which have been considered to have evolved as adaptations to drought or nutrient-deficient soils. However, the fact that the lineages carrying these features arose coincident with the rise to dominance of flammable C4 grasses and expansion of the savanna biome worldwide, and postdating the earlier origin of seasonal climates and the nutrient-poor, acid Cerrado soils suggests that such traits should be considered as adaptations to fire regimes. The nature of these features as adaptations to fire is further suggested by their absence or poor development in related lineages found in fire-free environments with similar edaphic conditions to the Cerrado and by their repeated independent origin in diverse lineages. We present evidence to demonstrate that the evolutionary barrier to entry to the Cerrado is a weak one, presumably because of the ease of evolution of the necessary adaptations to fire regimes for lineages inhabiting neighboring fire-free biomes.
189 citations
TL;DR: It is concluded that conifer success cannot be dismissed as being uniquely associated with habitats that are unfavorable for angiosperms, and all conifers can be characterized by a common set of functional attributes that allow them to exist in an important group of niches.
Abstract: Angiosperm radiation in the Cretaceous is thought to have profoundly diminished the success of the conifers, the other major woody plant group present at the time. However, today the conifers persist and often thrive despite their supposed inferiority in vegetative and reproductive function. By exploring this apparent conflict for global tree dominance, we seek here to reveal patterns that explain not only how the allegedly inferior conifers persist among angiosperms but also why some conifer groups became extinct in the Cretaceous. We find that despite the profound contrast between the dominant conifer families in the Southern and Northern Hemispheres, all conifers can be characterized by a common set of functional attributes that allow them to exist in an important group of niches, from high latitudes to the equator. In these environments, conifers are often highly efficient at outcompeting, outliving, or outsurviving angiosperms. Hence, we conclude that conifer success cannot be dismissed as being uniquely associated with habitats that are unfavorable for angiosperms.
135 citations
TL;DR: It is suggested that angiosperm taxa, which diversified since the early Cretaceous, evolved thinner roots with greater root length per unit of biomass invested (i.e., specific root length [SRL]) than earlier diverging taxa.
Abstract: On the basis of a synthesis of recent progress in belowground ecology, we advance and discuss a hypothesis that relates root trait evolution to the increased dominance of angiosperms into dry upland habitats and the decline of atmospheric CO2 concentration that began in the Cretaceous. Our hypothesis is built from examining patterns of fine root adaptations during the Cretaceous, when angiosperms dramatically diversified in association with arbuscular and ectomycorrhizal root-fungal symbionts. We then explore the potential effects of root adaptations and mycorrhizas on the geochemical carbon cycle. On the basis of phylogenetic analyses of root traits among extant plant species, we suggest that angiosperm taxa, which diversified since the early Cretaceous, evolved thinner roots with greater root length per unit of biomass invested (i.e., specific root length [SRL]) than earlier diverging taxa. We suggest that these changes in root morphology were facilitated by a decline in atmospheric CO2, which l...
125 citations
TL;DR: A number of functional aspects of fern biology are reviewed to include both gametophytic and sporophytic physiology, and it is possible that angiosperms engineered conditions that lead to aseasonal tropical forests and that wetter forests may have facilitated fern diversification.
Abstract: The Cretaceous period saw dramatic shifts in the functional plant biology of the Earth’s flora. This was an episode of explosive plant radiations that produced our modern angiosperm-dominated world. This period was also a time of great Pteridophytic diversification and experimentation and saw the rise of most extant fern lineages. Prominent among these was the widespread appearance of epiphytic species. In modern tropical forest canopies, epiphytic ferns often represent some of the most abundant taxa and can dominate epiphyte biomass. Yet from most perspectives, the epiphytic habitat is vastly different from the forest floor. What happened during the Cretaceous that led to such widespread epiphyte fern diversification? What are the traits that allow extant ferns to flourish in this dry, nutrient-poor, bright habitat? How did terrestrial ferns cope with this new habitat? We review a number of functional aspects of fern biology to include both gametophytic and sporophytic physiology. It is possible that ang...
105 citations
TL;DR: Focusing on newly discovered phylogenetic “hotbeds” of CAM and C4 evolution will allow for inclusion of relevant C3 taxa and a finer evaluation of the possible environmental and organismal traits that would strongly favor the evolution of one syndrome over the other.
Abstract: Crassulacean acid metabolism (CAM) and C4 photosynthetic syndromes have much in common: they employ a shared biochemical pathway that enables the concentration of CO2 inside plant cells, they are both considered to be adaptations to stressful environments, and they are both arguably among the most convergent of complex traits, having each evolved multiple times in various plant lineages. They are also both signature elements of stress-adapted floras the world over and play fundamental roles in the ecological success of flowering plants. In spite of these similarities, the obvious phenotypic and ecological differences between certain groups of fully optimized C4 and CAM plants have led us to generally view these syndromes as very distinct ecological adaptations. A broad look at the distribution of CAM and C4 plants across a very large phylogeny of angiosperms highlights that while CAM photosynthesis seems to have evolved more often, both CAM and C4 origins show tight and overlapping clustering in many regi...
101 citations
TL;DR: Tracheid anatomical variables improved the understanding of climate effects on tree growth and wood formation under harsh environmental conditions, as those experienced in continental Mediterranean climates, where limiting factors show multiple shifts across the year.
Abstract: A detailed understanding of how the climate models the hydraulic system of trees is still lacking, in spite of the need to understand tree response to the ongoing process of climatic change. A systematic correlation of tracheid anatomical features with climate has not been implemented in Mediterranean ecosystems, where climatic change is expected to be particularly intense. We measured ring width and cell number—in addition to intraring position, lumen size, and wall thickness of tracheids—in 10 Juniperus thurifera individuals from north-central Spain. We used this information to perform an exploratory analysis of how these parameters correlated with climatic variables in 1965–2004. Cell number and ring width shared a relatively similar climatic signal, whereas the anatomical variables provided differentiated and diverse signals about climatic conditions during their formation. Earlywood and latewood tracheids differed in controlling factors, with earlywood tracheid size and wall thickness being positivel...
77 citations
TL;DR: Angiosperm pollen tube walls consist largely of callose and contain far less material than do tube walls of other seed plants, which have little or no callose but high cellulose and pectin content.
Abstract: Early angiosperm history was marked by a shift from a long to an exceptionally brief fertilization process. Ovules and their associated female gametophytes became greatly reduced in size, resulting in the precocious production of eggs and a greatly abbreviated pollination-to-fertilization period. The shift to small ovules was accompanied by the origin of an enclosing carpel (angiospermy) and associated accessory organs that together formed a small and ephemeral reproductive shoot, or flower. An unappreciated innovation, which arose within the context of these reductions in size and the longevity of reproductive tissues, was a set of traits that gave ancestrally slow-growing pollen tubes the capacity to evolve faster growth rates. Angiosperm pollen tube walls consist largely of callose and contain far less material than do tube walls of other seed plants, which have little or no callose but high cellulose and pectin content. This and other aspects of their novel wall architecture are hypothesized t...
62 citations
TL;DR: This review investigates patterns of growth form diversification in Piperales, an early-diverging lineage and the most morphologically diverse clade among magnoliids, as well as the biomechanical significance of developmental characters, such the organization, loss, and gain of woodiness.
Abstract: A striking feature of early angiosperm lineages is the variety of life forms and growth forms, which ranges from herbs, aquatic herbs, climbers, and epiphytes to woody shrubs and trees. This morphological and anatomical diversity is arguably one of the factors explaining how angiosperms dominate many ecosystems worldwide. However, just how such a wide spectrum of growth forms has evolved in angiosperms remains unclear. In this review, we investigate patterns of growth form diversification in Piperales, an early-diverging lineage (with stem age estimated at 201–128 Myr ago) and the most morphologically diverse clade among magnoliids. We outline patterns of growth form diversity and architecture as well as the biomechanical significance of developmental characters, such the organization, loss, and gain of woodiness. Asaroideae and Saururaceae are terrestrial as well as semiaquatic to aquatic herbaceous perennials bearing rhizomes. The Aristolochioideae and Piperaceae show higher levels of growth form divers...
60 citations
TL;DR: The evolution of flammable grasses is the latest expression of angiosperm innovation, generating even more frequent fires capable of carving into forests, particularly after the spread of C4 grasses from ∼8 Ma.
Abstract: Fires have been burning plants since the early Devonian and were common in the Mesozoic, before angiosperms became prominent. Fires were common in the Cretaceous, when angiosperms first spread to cover significant areas of the world. We suggest that this spread was facilitated by intrinsic angiosperm properties that altered fire regimes in two fundamental ways. The first was to promote more frequent fires than the slower-growing gymnosperms that they replaced. The high productivity of angiosperms would have fueled more frequent fires, while reproductive innovations allowed for more rapid recovery, particularly in upland areas too dry for ferns. The evolution of flammable grasses is the latest expression of angiosperm innovation, generating even more frequent fires capable of carving into forests, particularly after the spread of C4 grasses from ;8 Ma. The second major impact of angiosperms on fire was the development of forests. Closed broadleaved forests fundamentally changed fire regimes by producing a vegetation structure that intrinsically excludes fires. No conifer analogues for fire-excluding forests seem to exist today or to have existed in the evolutionary past. Both fire-promoting and fire-excluding ecosystems are a product of angiosperm innovations. While these novel ecosystems may have caused the extinction of several ancient lineages, ferns and conifers still persist within them. One conifer lineage, the genus Pinus, has shown remarkable adaptability to highly flammable ecosystems, including frequently burned C4 grasslands.
58 citations
TL;DR: Numerical cladistic analysis of anatomically preserved seed cones yields a well-resolved phylogeny of crown and stem group Pinaceae that is roughly concordant with the results of analyses that include living species only.
Abstract: This study describes a specimen that extends the oldest fossil evidence of Pinus L. to the Early Cretaceous Wealden Formation of Yorkshire, UK (131–129 million years ago), and prompts a critical reevaluation of criteria that are employed to identify crown group genera of Pinaceae from anatomically preserved seed cones. The specimen, described as Pinus yorkshirensis sp. nov., is conical, 5 cm long, and 3.1 cm in maximum diameter. Bract/scale complexes are helically arranged and spreading. Vasculature of the axis forms a complete cylinder with few resin canals in the wood, and the inner cortex is dominated by large resin canals. Bracts are short, with two resin canals, and separate from the scale base laterally. Distally, the ovuliferous scales broaden and thicken to form a rhomboidal apophysis with a dorsal umbo, characters found only in the genus Pinus among living conifers. Resin canals enter the ovuliferous scale abaxial to the vascular tissue, which divides distally to form a row of adaxially convex bu...
47 citations
TL;DR: Relationships among genera of the tribe Episcieae are investigated using an array of chloroplast DNA, nuclear ribosomal genes, and low-copy nuclear genes to provide resolution for the monophyly of the genera and relationships among themonophyletic groups.
Abstract: The Gesneriaceae is a family known for convergent evolution of complex floral forms. As a result, defining genera and resolving evolutionary relationships among such genera using morphological data alone has been challenging and often does not accurately reflect monophyletic lineages. The tribe Episcieae is the most diverse within Neotropical Gesneriaceae in terms of its number of species and morphological diversity. As a result, defining genera using floral characters has been historically troublesome. Here we investigate relationships among genera of the tribe using an array of chloroplast DNA, nuclear ribosomal genes, and low-copy nuclear genes to provide resolution for the monophyly of the genera and relationships among the monophyletic groups. All known genera in the tribe (with the exception of the monospecific Lampadaria) have been sampled, and most have been sampled to provide an assessment to determine their monophyly. Of the 17 genera in the tribe that comprise more than a single species, we hav...
TL;DR: Evidence from extant comparative biology and the Early Cretaceous fossil record of leaves and wood do not support the hypotheses that vessels improved drought tolerance of angiosperms, increased angiosperm’s photosynthetic abilities, or provided an immediate leap in hydraulic capacity.
Abstract: A hypothesized advantage of the building block of the angiosperm vascular network, the vessel, is often cited as a critical innovation that elevated the competitive abilities of early angiosperms above nonangiosperms during the Cretaceous. Here we synthesize recent discoveries on the hydraulic functions of living basal angiosperm lineages with evidence from the fossil record to trace the early evolutionary significance of vessels in the early ecophysiological radiation of angiosperms. Evidence from extant comparative biology and the Early Cretaceous fossil record of leaves and wood do not support the hypotheses that vessels improved drought tolerance of angiosperms, increased angiosperm’s photosynthetic abilities, or provided an immediate leap in hydraulic capacity. Instead, later tuning of vessel structure for increased flow efficiency—in particular, by the evolution of simple perforation plates—enabled major increases in xylem hydraulic efficiency.
TL;DR: This work investigated the floral development of five annual, unicarpellate species of Delphinium, focusing on perianth organization, and showed that the nectar-storing organ in these species results from the postgenital fusion of two primordia of the internal perian fourth whorl.
Abstract: Delphinieae (Ranunculaceae) comprise ∼650 species of temperate herbs in Eurasia, North America, and Africa. Their zygomorphic flowers have been the object of numerous studies in morphology, ecology, and developmental genetics, and new phylogenetic insights make it timely to synthesize knowledge about their evolution. Key features of Delphinieae flowers are unusual nectaries consisting of paired organs of the inner perianth whorl that are completely enclosed by a single dorsal organ of the outer whorl. We investigated the floral development of five annual, unicarpellate species of Delphinium, focusing on perianth organization. The results show that the nectar-storing organ in these species results from the postgenital fusion of two primordia of the internal perianth whorl. Eleven floral traits traced on a phylogeny of Delphinieae reveal only two homoplasies in the perianth, namely, the nightcap shape of the dorsal organ of the external perianth whorl and the reduction of the internal perianth whorl to two ...
TL;DR: Xylem traits are linked to differences in life history types in fynbos species, with most taxa from the drier site having greater levels of cavitation resistance and lower levels of xylem-specific hydraulic conductivity than taxaFrom the wetter site.
Abstract: Xylem safety and efficiency were analyzed for stems of evergreen shrubs that inhabit fynbos communities in the Mediterranean-type climate region of South Africa. We hypothesized that species with different life history types would differ in xylem function on account of their different regeneration niches. Comparisons were made among postfire nonsprouters, facultative sprouters, obligate sprouters, and opportunists. Measurements included xylem resistance to water stress‐induced cavitation (xylem safety) and xylem-specific hydraulic conductivity (xylem efficiency) at a dry site and at a wetter site. Life history types differed in hydraulic traits: xylem safety was greater in life history types with disturbance-dependent recruitment. By contrast, water stress resistance was lowest in postfire obligate resprouters that recruit seedlings during fire-free intervals in the litter layer of shady microsites. Among life history types, greater xylem safety came at the cost of reduced hydraulic efficiency. This pattern was also observed between field sites, with most taxa from the drier site having greater levels of cavitation resistance and lower levels of xylem-specific hydraulic conductivity than taxa from the wetter site. We conclude that xylem traits are linked to differences in life history types in fynbos species.
TL;DR: The results show that the ancestor of Cinchonoideae and its sister, Ixoroideae, was present in South America during the Late Cretaceous and dispersed to the Paleotropics no later than the Eocene, and the findings of fossils of Cephalanthus in Europe and western Siberia support its presence in the boreotropical forests.
Abstract: The Rubiaceae is the fifth largest plant family and is found on all continents, mostly in (sub-)tropical regions. Despite a large representation of Rubiaceae in the Paleotropics, the subfamily Cinchonoideae has its primary distribution in the Neotropics. Within the Cinchonoideae only two tribes, Naucleeae and Hymenodictyeae, have Paleotropical centers of distribution. In this study, we used information from five chloroplast DNA markers and fossil data to investigate when the subfamily was established in the Neotropics as well as major subsequent dispersal events within and out of the Neotropics and within the Paleotropics. Our results show that the ancestor of Cinchonoideae and its sister, Ixoroideae, was present in South America during the Late Cretaceous. Dispersal to Central America was estimated to occur during the Early Paleocene, and subsequent dispersals to the Caribbean islands occurred during the Oligocene–Miocene. The ancestor of Naucleeae and Hymenodictyeae dispersed to the Paleotropics no late...
TL;DR: A survey of the fossil record demonstrates that most anatomical traits that are now unique to the angiosperms were more broadly distributed among extinct lineages, which may have enabled a greater range of architectural possibilities.
Abstract: Angiosperms represent more than three-quarters of all land plant species despite existing for only a quarter of land plant history, inspiring much interest in understanding what aspects of angiosperm biology may have enabled their unparalleled success. However, comparative study of extant plants cannot fully address the basis of angiosperm dominance because most living nonflowering plants are members of recently radiating lineages as young or younger than the flowering plants and, thus, are a highly biased sampling of the full 400 Myr history of vascular plant diversity. Here, a survey of the fossil record demonstrates that most anatomical traits that are now unique to the angiosperms were more broadly distributed among extinct lineages. However, the growth capacities of angiosperms are likely to have been uniquely high for all of vascular plant history and may have enabled a greater range of architectural possibilities, including the fast-growing annual herbs that represent a large proportion of angiospe...
TL;DR: Parallel changes in petal size and color in selfing populations from two climatically different regions plus the maintenance of differences in flower size andcolor between large- and small-flowered populations when grown in a common glasshouse environment suggests genetic differentiation in these traits associated with mating system evolution.
Abstract: Floral traits used to attract and reward pollinators should become vestigial during the evolution of self-fertilization from outcrossing due to the reduced fitness benefits of investing in pollinator attraction. However, few traits have been studied, and covariation with outcrossing is rarely evaluated using genetic estimates of the mating system. We examined covariation between petal size and color and genetic estimates of outcrossing among populations of the yellow-flowered, bee-pollinated Camissoniopsis cheiranthifolia that exhibit striking variation in the mating system. We measured brightness, chroma, and hue, using a spectrophotometer, and petal size, using image analysis for flowers sampled in the field from 25 populations across the species’ geographic range. Petals were brighter with higher chroma and lower hue (less red) in large-flowered populations than in small-flowered populations. Petal size, brightness, and chroma also correlated positively with the proportion of seeds outcrossed estimated...
TL;DR: The results indicate that peripheral populations may experience higher genetic drift and lower gene flow than their central counterparts, possibly because of smaller population sizes, spatial isolation, and a more complex landscape structure.
Abstract: A common assumption in ecology and evolutionary biology is that genetic diversity declines and differentiation increases toward the edge of a species’ geographic range, where populations tend to be smaller and more isolated. We tested these predictions in a characteristic Eurasian steppe plant, Stipa pennata, by inspecting 230 AFLP bands in 26 populations (345 individuals) along a 3300-km longitudinal gradient from the range core, in Russia, to the range periphery, in central Europe. Overall, our study species showed low genetic diversity within populations (mean proportion of polymorphic ) and moderately high genetic differentiation among them (mean ). As predicted, genetic diversity declined significantly from the range core to the periphery but was not correlated with population size. Pairwise genetic differentiation was significantly higher among peripheral populations than central populations but did not show a pronounced relationship with geographic distance. Our results indicate that peripheral pop...
TL;DR: Petal surface micromorphology in relation to pollination type is examined, finding that the almost complete elimination of PCS during the shift of pollination syndrome from bee to birds may be adaptively driven as a both probird and antibee trait.
Abstract: Bird pollination has evolved in four species of Macaronesian Lotus from a bee-pollinated ancestor. The transition is associated with the modification of several floral traits, including flower color and size, relative size and orientation of the petals, and nectar composition and quantity. Here, we examine petal surface micromorphology in relation to pollination type, using SEM and LM. In the bee-pollinated Lotus (the majority of the genus), papillose conical cells (PCS) are the most abundant epidermal type on dorsal and lateral petals. However, bird-pollinated species completely lack PCS on their dorsal petals and have only a small patch of PCS in a highly localized region of the lateral petal. In the bee-pollinated species (including those most closely related to the bird-pollinated species), PCS develop early in floral development. In contrast, the small amount of residual PCS in bird-pollinated species forms later in development, after the other two major epidermal types have been formed. The almost c...
TL;DR: The combination of strongly ornamented monocolpate pollen grains permanently united in tetrahedral tetrads is unusual and to the best of the authors' knowledge has not been reported previously in a gymnosperm.
Abstract: Ricciisporites tuberculatus Lundblad is a prominently sculptured palynomorph that is permanently united in tetrads. This palynomorph has a wide geographic distribution and reaches a stratigraphically important acme in the Late Triassic of Europe, Greenland, and Arctic Canada. This palynomorph has not yet been found in situ in a fossilized reproductive structure, and consequently its botanical affinity is unclear. Some authors have suggested that R. tuberculatus was produced by a seed plant, but others have suggested that this palynomorph was produced by a liverwort comparable to Riccia. In order to clarify the botanical affinity of R. tuberculatus, we have analyzed its morphology using SEM and TEM. Individual grains within the tetrad are equipped with a single distal colpus, and the ultrastructure of the palynomorph wall is characterized by a granular inner sexine and an electron-dense laminated nexine. These morphological features ally R. tuberculatus to the gymnosperms. The combination of strongly ornam...
TL;DR: The role of size and shape leaf covariation in the evolutionary processes of white oaks is highlighted and its effect on species differentiation is tested.
Abstract: A combined genetic and morphometric approach was used to study leaf shape and size variability among three sympatric and interfertile white oak species (Quercus frainetto, Quercus petraea, and Quercus pubescens) sampled in a mixed forest in central Italy. Leaf shape and size were analyzed separately to discriminate species, to identify unique leaf shape traits, and to analyze the relationships between hybrid phenotypes and their parental species. In addition, the covariation of leaf shape and size (i.e., allometry) was tested at the intraspecific level, and the differences in allometric trajectories were compared among species and hybrids. Finally, size correction of leaf shape data allowed quantification of the contribution of allometry to total variability and testing of its effect on species differentiation. Within pure oak species, leaf allometry was a significant component of leaf variation related to environmental variability, while when hybridization occurred leaf allometry was affected by the inhe...
TL;DR: This first experimental sequence on extended dehardening in bryophytes counters the assumption that field shoots hydrated longer than four consecutive days are entirely dehardened and provides evidence that mosses can harden to DT without relying on external cues such as partial hydration.
Abstract: Dehardening (deacclimation) to water stress is an integral phase of desiccation tolerance (DT) in bryophytes. Shoots of the desert moss Syntrichia caninervis were harvested and dehardened after exposure to field CO2 concentrations of 380 ppm (ambient) and 550 ppm (elevated). The dehardening period consists of three phases, with shoots from the first phase (3–7 d) the least able to recover from a rapid-drying event and the second (12–18 d) and third (21–27 d) phases characterized by shoots hardening to desiccation and approaching control levels. Response variables following this pattern include tissue chlorosis, protonemal emergence and area, shoot growth resumption, total regenerative shoot production, and probability of fungal attack. Dehydrin levels did not increase over time during the 27-d experimental hydrating period and thus could not account for the observed constitutive hardening to DT. This first experimental sequence on extended dehardening in bryophytes counters the assumption that field shoot...
TL;DR: Crystallized or spheroidal storage substances contained in the axial parenchyma also suggest that the local environment had become unstable by at least the Guadalupian.
Abstract: A novel coniferous tree trunk, Plyophyllioxylon hulstaiense gen. nov. et sp. nov., is described from the Lower Shihhotse Formation (Guadalupian, Permian) of the Hulstai coalfield, in the Inner Mongolia Autonomous Region of northern China. The decorticated tree trunk is permineralized and is characterized by broad eustele and well-developed pycnoxylic secondary xylem. The parenchymatous pith is up to 30 mm in diameter, with the central portion septated by diaphragms and the perimedullary cells continuous. The primary xylem is endarch; tracheids from protoxylem to metaxylem possess helical, annular, and scalariform/reticulate thickenings. The monarch leaf traces initiate from the pith margin and are arranged according to a helical phyllotaxy of 3/24 or 4/24. Tracheids in the secondary xylem have uni- to biseriate araucarioid pits; cross field pits are cupressoid. Ray cells are parenchymatous, with smooth walls, uni- to biseriate. Vertically aligned or isolated axial xylem parenchyma is interpreted as an evo...
TL;DR: Using reverse transcription polymerase chain reaction, it is shown that most RAD copies are expressed across floral and leaf tissues in Lonicera × bella, which favors the hypothesis that a similar interaction between CYC and RAD may occur outside of the Lamiales.
Abstract: Evidence from Antirrhinum majus indicates that transcription factors CYCLOIDEA (CYC), DIVARICATA (DIV), and RADIALIS (RAD) play a role in specifying floral symmetry. In bilaterally symmetrical flowers, CYC and RAD are implicated in dorsal identity, while DIV patterns ventral identity. In this study, we examined duplication events within the RAD-like gene family in Dipsacales and report the phylogenetic relationships of the RAD-like genes across Pentapetaleae. Like CYC-like and DIV-like genes, we found three Pentapetaleae clades of RAD-like genes: RAD1, RAD2, and RAD3, with AmRAD in the RAD2 clade. Unlike CYC-like and DIV-like gene families, only one of these duplications appears to have taken place around the diversification of the Pentapetaleae: RAD1 spans the monocots and eudicots, while RAD2 and RAD3 are Pentapetaleae specific. We found additional duplications within these gene clades in Dipsacales, especially within the Morinaceae, Dipsacaceae, and Valerianaceae, which also contain additional duplicat...
TL;DR: It is demonstrated that two main osmundaceous reproductive morphologies; i.e., differentiated reduced or unreduced fertile laminae were already present and widespread in Gondwana by this time, and suggested that fossil representatives are better placed in morphotaxa than in any current genus.
Abstract: Two new compression-impression species of the Osmundaceae described from reproductive and vegetative remains are erected for the first time from the Early Jurassic of Argentina. Todites cacereii sp. nov. and Osmundopsis rafaelii sp. nov. demonstrate that two main osmundaceous reproductive morphologies; i.e., differentiated reduced or unreduced fertile laminae were already present and widespread in Gondwana by this time. On the basis of a discussion of relevant morphological characters, the phylogenetic meaning of the fossils Todites and Osmundopsis is explored. Likewise, the systematics and taxonomy of fossil taxa and their relationships with modern ones are discussed in light of current hypotheses. In this regard, because clear synapomorphies or apomorphies are not yet fully understood, it is suggested that fossil representatives are better placed in morphotaxa (Todites, Osmundopsis) than in any current genus. Nonetheless, the clear record of characters of the leptopteroid clade by the early Jurassic pro...
TL;DR: Angiosperm woods from the Campanian Crevasse Canyon Formation and the Maastrichtian Jose Creek Member of the McRae Formation are described, with Baasia and Fulleroxylon representing the first North American fossil wood records of Celastraceae and Myrtaceae, respectively.
Abstract: Late Cretaceous angiosperm woods from the Western Interior of North America are poorly known relative to palynomorphs and leaf macrofossils. In this report we describe angiosperm woods from the Campanian Crevasse Canyon Formation and the Maastrichtian Jose Creek Member of the McRae Formation, in south-central New Mexico. New taxa include Baasia armendarisense (Celastraceae), Fulleroxylon armendarisense (Myrtaceae), and Pygmaeoxylon paucipora (magnoliid of uncertain affinities). Previously described taxa include Metcalfeoxylon (eudicots), Paraphyllanthoxylon (most likely Laurales), and Platanoxylon (Platanaceae). Tree habit is indicated for Metcalfeoxylon, which is known from in situ stumps with a maximum basal diameter of 0.75 m, and for Baasia and Paraphyllanthoxyon, which are known from axes at least 0.14 m in diameter. Baasia and Fulleroxylon represent the first North American fossil wood records of Celastraceae and Myrtaceae, respectively. Baasia also indicates that within Celastraceae, the pattern of...
TL;DR: This study is the first to investigate the relation between pollination intensity and female fertility in a wind-pollinated species and provides support for the contribution of gametophytic competition to sex ratio variation in plants.
Abstract: Variation in pollination intensity can influence the degree of gametophytic competition with diverse consequences for plant fitness. Such effects should be particularly important in wind-pollinated plants because they commonly possess uniovulate flowers. In several dioecious species, competition between female- and male-determining microgametophytes has been proposed as a cause of female-biased sex ratios. Here, we examine functional relations among pollination intensity, seed set, sex ratios, and sporophyte vigor in Rumex hastatulus, a wind-pollinated, dioecious plant. Using controlled pollinations, we applied a range of pollen grain numbers (1–71) to female flowers. Pollination intensity significantly predicted percent seed set, which was >80% when more than 15 pollen grains were added to stigmas. We estimated that the proportion of pollen grains participating in fertilization was 0.28 and the proportion of fertilized ovules developing into seed was 0.89. Overall, progeny sex ratios were female biased (...
TL;DR: Ginkgo cranei is the only Tertiary species of the genus described in which the ovulate organs are studied in some detail and corroborates the hypothesis that modern Ginkgo evolved from its ancestors by reduction and is helpful to classify Cenozoic ginks in a natural system.
Abstract: The evolutionary history of Ginkgo is poorly understood for the Cenozoic Era because of the rarity of fossil reproductive organs. We here describe a new species, Ginkgo cranei sp. nov., on the basis of well-preserved ovulate organs and associated leaves from the Upper Paleocene Sentinel Butte Formation of North Dakota, USA. The ovulate organ is of the modern type, which lacks a pedicel supporting each of the two ovules. The ovules are seated in separate collars directly attached to the peduncle, but only one of them is mature. Stomatal complexes are mostly amphicyclic, with deeply sunken guard cells and slightly raised subsidiary cells. They are sparsely distributed among epidermal cells characterized by domelike, strongly bulging periclinal walls and developed anticlinal wall flanges in integument and collar cuticles. The associated leaves are generally similar to the ovulate organ in cuticular structure. Ginkgo cranei is the only Tertiary species of the genus described in which the ovulate organs are st...
TL;DR: Fossil winged seeds from the early Miocene of Ethiopia represent the earliest and only definitive record of the ecologically and economically important legume genus Newtonia (Fabaceae: “Mimoseae”) and provide evidence that tropical moist forest persisted on the Ethiopian Plateau into the earlyMiocene.
Abstract: Numerous fossil winged seeds from the early Miocene (22–21 Ma) of Ethiopia represent the earliest and only definitive record of the ecologically and economically important legume genus Newtonia (Fabaceae: ‘‘Mimoseae’’). These fossils represent a new species and provide evidence that tropical moist forest persisted on the Ethiopian Plateau into the early Miocene.
TL;DR: The features of sheath cells evidenced by ZIO, such as the presence of Golgi bodies and smooth endoplasmic reticulum, indicate that these cells have secretory activity and participate in producing secretions.
Abstract: Pterodon pubescens Benth., a legume of the Brazilian Cerrado, produces oil that is employed in folk and conventional medicine. In this study, we investigated the distribution, structure, and secretion mechanisms of the secretory cavities in the mature embryo, seedlings, and vegetative organs of adult plants of P. pubescens, using light and electron microscopy as well as cytochemical methods (ZIO). Secretory cavities occur in the epicotyl and eophylls of seedlings and in the primary stem and leaves of adult plants, and they are absent in the embryo. These cavities are constituted by a wide lumen and a uniseriate epithelium of secretory cells. A parenchyma sheath surrounds each gland. Oils and terpenes were histochemically detected in the epithelium and in the lumen of the cavities. Ultrastructurally, epithelial cells showed proliferation of endoplasmic reticulum, abundant mitochondria, polyribosomes, polymorphic plastids, and lipid droplets. Multivesicular bodies and paramural bodies were also common in th...