Plant evolution

The foliar epidermis micromorphology of 24 species of Alchemilla (Rosaceae) was studied by scanning electron microscopy (SEM). The trichomes were examined on both abaxial and adaxial leaf surfaces. Two trichome type classes were recognized: the straight cylindrical appressed-subappressed and the straight cylindrical -flat ribbon-shape hairs. The first type was dominant and consisted of two subtypes. Glandular trichomes were either one-celled stalk with capitated head cell or a three-four-celled stalk with subglobular head cell. Epicuticular waxes were composed of two main types, including film (the crust, smooth layer) and crystalloids (membrane and irregular, rosette, aggregate platelets and plates). In all examined species, the stomata were situated lower than the epidermal layer and their shape varied from oval to round and elliptical. Three type of epicuticular wax distribution on the stomata surface were recorded. The foliar epidermis micro morphological characters proved to play an outstanding role in the taxonomy and classification of the genus.

This paper introduces a functional-structural plant model based on artificial life concepts and L-systems. This model takes into account realistic physiological rules, the architecture of the plants and their demography. An original benefit of this approach is that it allows the simulation of plant evolution at both functional and life-history levels implementing mutations to the L-systems and a set of genetic parameter values. The conducted experiments focus on the evolutionary emergence of different life history strategies in an environment with heterogeneous resource availability and disturbance frequency. It is found that, depending on the encountered conditions, the plants develop three major strategies classified as competitors, stress-tolerators and ruderals according to Grime's CSR theory. Most of the evolved characteristics comply with theoretical biology or field observations on natural plants. Besides these results, our modelling framework is highly flexible and many refinements can be readily implemented depending on the issues one intends to address. Moreover, the model can readily be used to address many questions at the interface between evolutionary ecology, plant functional and community ecologies and ecosystem ecology.

A well-resolved phylogeny of Flaveria is used to infer evolutionary relationships among species, biogeographical distributions, and C4 photosynthetic evolution. Data on morphology, life history, and DNA sequences (chloroplastic trnL-F, nuclear ITS and ETS) for 21 of 23 known species were collected. Each data set was analyzed separately and in combination using maximum parsimony and Bayesian analyses. The phylogeny of Flaveria is based on the combined analysis of all data. Our phylogenetic evidence indicates that C3 Flaveria are all basal to intermediate (C3-C4 and C4-like) and fully expressed C4 Flaveria species. Two strongly supported clades (A and B) are present. Using this phylogeny, we evaluate the current systematics of the genus and suggest the removal and reevaluation of certain taxa. We also infer the center of origin and dispersal of Flaveria species. Multiple origins of photosynthetic pathway intermediacy in Flaveria are recognized. C3-C4 intermediacy has evolved twice in the genus and is found to be evolutionarily intermediate in clade A, but not necessarily in clade B. C4-like photosynthesis is also derived once in each clade. In addition, fully expressed C4 photosynthesis may have evolved up to three times within clade A.

Originally coined to emphasize morphological differences, ‘microphyll’ and ‘megaphyll’ became synonymous with the idea that vascular plant leaves are not homologous. Although it is now accepted that leaves evolved independently in several euphyllophyte lineages, ‘megaphyll’ has grown to reflect another type of homology, that of euphyllophyte leaf precursor structures. However, evidence from the fossil record and developmental pathways fails to indicate homology and suggests homoplasy of precursor structures. Thus, as I discuss here, ‘megaphyll’ should be abandoned because it perpetuates an unsupported idea of homology, leading to misconceptions that pervade plant biology thinking and can bias hypothesis and inference in developmental and phylogenetic studies. Alternative definitions are needed that are based on development and phylogeny for different independently evolved leaf types.

Throughout the history of the classification of extant ferns (monilophytes) and lycophytes, familial and generic concepts
have been in great flux. For the organisation of lycophytes and ferns in herbaria, books, checklists, indices and spore
banks and on the internet, this poses a problem, and a standardized linear sequence of these plants is therefore in great
need. We provide here a linear classification to the extant lycophytes and ferns based on current phylogenetic knowledge;
this provides a standardized guide for organisation of fern collections into a more natural sequence. Two new families,
Diplaziopsidaceae and Rhachidosoraceae, are here introduced.

Background
Experimental manipulations of floral nectar in food deceptive species can reveal insights
into the evolutionary consequences of the deceptive strategy. When coupled to pollen tracking,
the effects of the deceptive pollination syndrome on both male and female reproductive
success may be quantified. Attraction of pollinators in deceit-pollinated species often relies
on producing a conspicuous floral display which may increase visibility to pollinators, but inturn
may increase within plant selfing.
Methodology
To understand the role of deception in Orchidaceae reproduction we studied Cypripedium
candidum. All species of the Cypripedium genus employ a generalized food deceptive pollination
strategy and have been suggested as a model system for the study of pollinator
deception. We conducted a nectar addition experiment that randomly assigned the four
plants closest to a transect point to receive one of four histochemical dyes. Two individuals
selected for nectar addition in each of altogether 25 blocks received 2μl of 25% sucrose
solution in the labellum of each flower, while two others received no artificial nectar. Number
of fruits produced, fruit mass and fruit abortion were scored at the end of the four-month
experiment.
Results
Nectar addition increased (p<0.0001) self-pollination and pollen discounting by nearly 3x,
while plants not receiving nectar had greater (p<0.0001) numbers of non-self pollinia deposited
and lower rates of pollen discounting. There was a non-significant (p = 0.0645) trend for
deceptive plants to set more fruit, while presence of nectar did not affect pollen export.
Conclusions
This study demonstrates the adaptive advantages of food deception by showing a concurrent
reduction in particular male and female functions when a food reward is restored to a deceptive flower. We found generalized food deception to not only decrease inbreeding
depression in the system, but concurrently have no effect on pollinator attraction and fruit
set when compared with rewarding flowers.

Mathematical models of fluid flow through and embolism resistance of extinct plant xylem provide insight into the ecology and physiology of individual fossil plants. Disparate lineages of vascular plants exhibit a variety of ecophysiological strategies: extreme adaptations for maximum flow and maximum safety have both been documented in living and extinct plants. Analysis of early-diverging vascular plants and early-diverging seed plants shows that a variety of hydraulic strategies were pursued early in the evolution of terrestrial plants, especially during the Devonian and Carboniferous Periods. Analysis of five species of the Lower and Middle Devonian trimerophyte genus Psilophyton indicates that some species possess low-resistance metaxylem tracheids with numerous, highly porous pits and relatively low embolism resistance, whereas other species contain xylem with higher embolism resistance and lower hydraulic conductivity. Despite a simple vegetative morphology, physiological analysis of several Psilophyton fossils suggests that species possessed distinct ecophysiological strategies and there may be cryptic functional diversity within other trimerophyte genera. When integrated with previous hydraulic analyses of extinct and extant plants, including the Lower Devonian stem group lycophyte Asteroxylon mackiei; a series of Carboniferous stem group seed plants, including Medullosa, Callistophyton, and Lyginopteris; eleven genera of extant conifers and cycads; two species of ginkgophytes, and others, the occupation of tracheid-based hydraulic ecospace can be mapped. Soon after the evolution of vascular tissue in land plants, the high-conductivity/low-safety-margin space was occupied; particularly by plants that grew in the tropical lowland swamps during the Carboniferous Period. Upon the disappearance of the coal swamp floras during the Permian Period, that portion of the ecospace may have remained unoccupied until the evolution of angiosperms with vessels in the Cretaceous Period. Taken as a whole, the evolution of vascular tissue during (and after) the terrestrialization process records several physiological adaptive radiations, occurring early in plant evolution, which likely had major effects on global environmental and biogeochemical processes.

 Type specimens are permanently preserved biological specimens that fix the usage of species names. This method became widespread from 1935 onwards and is now obligatory.
 WeusedDNAsequencingoftypesandmorerecentcollectionsofwildandcultivatedmelons to reconstruct the evolutionary history of the genus Citrullus and the correct names for its species.
 WediscoveredthatthetypespecimenofthenameCitrulluslanatus,preparedbyaLinnaean collector in South Africa in 1773, is not the species now thought of as watermelon. Instead, it is a representative of another species that is sister to C. ecirrhosus, a tendril-less South African endemic. The closest relative of the watermelon instead is a West African species. Our nuclear and plastid data furthermore reveal that there are seven species of Citrullus, not four as assumed.  Our study implies that sweet watermelon originates from West, not southern Africa as previously believed, and that the South African citron melon has been independently domesticated. These findings affect and explain numerous studies on the origin of these two crops that led to contradictory results because of the erroneous merging of several distinct species.

Recently discovered megafossil plant remains in late Early Permian (Kungurian) marine sediments on northern Axel Heiberg Island, Canadian Arctic Archipelago, provide a much needed datum point for paleobiogeographic considerations in this part of North America. The fossil plants represent at least ten families belonging to several major groups (sphenopsids, ferns, pteridosperms, ginkgos, cordaitaleans, and conifers). The conifers Rufloria and Walchia are the most commonly represented taxa, while other gymnosperms constitute much of the remaining collection. Lycopsids are absent and sphenopsids as well as ferns are present, but rare. The plant material probably originated from Crockerland and has a complex taphonomic history. There appears to be a strong phytogeographic connection with the Angaran floral realm. In addition, some floral elements occurring here are known mostly from the Early Mesozoic elsewhere. These findings support the idea that plant evolution was most intensive in extrabasinal settings; with migration into the depositional lowlands often occurring at times when climatic conditions became favorable for range expansion out of the uplands. The Axel Heiberg Island flora is another datum point for rare, but significant late Early Permian age floras on the North American continent. ß

Rhizome morphology of 18 Zingiberales species growing in situ in lowland Ecuadorian rainforest (Payamino) covering six of the eight families of the order is presented. Phenetic and morphological analyses reveal two strategies that vary starkly in their mode of construction and geometry. Furthermore, parsimony-based character evolution in a resolved phylogenetic framework identifies convergent evolution of these strategies. The two strategies uncovered by the phenetic and morphological analyses are correlated with branching localization and timing: species showing delayed, non-positional–preferential branching exhibit poorly predictable, non-geometric rhizomes whereas species exhibiting immediate branching occurring at specific internodes display predictable, highly geometric rhizome morphologies. Hence, the control of two simple developmental parameters defines two distinct modes of construction in basitonically branched, rhizomatous plants. Multiple switches in the state of these characters during the evolution of Zingiberales resulted in diversification and convergence of rhizome morphologies in the order.

El estudio de las floras del pasado, su diversidad y evolución a través del tiempo es el tema central de la investigación paleobotánica, ya sea a través del análisis de impresiones de hojas, frondes, flores, frutos o semillas, leños permineralizados, o también el estudio de componentes microscópicos como los granos de polen, esporas, y algas. resulta interesante tener en cuenta la importancia de las plantas como principal fuente de alimento del reino animal y como proveedor de los hábitats donde se desarrollan, características estas que han ido cambiando a través del tiempo. Muchos grupos de plantas se extinguieron mientras que otros se originaron y diversificaron planteando numerosos interrogantes a todos los que nos dedicamos al estudio de las floras del pasado. Preguntas frecuentes como ¿cuáles fueron los principales forzantes que modelaron sus cambios y evolución? ¿cuándo, y en qué ambientes, se originaron algunos grupos de plantas, como por ejemplo las plantas con flor? ¿cómo y por qué algunos grupos sobre-Rev. Mus. Argentino Cienc. Nat., n.s. 14(2): 175-187, 2012 ISSN 1514-5158 (impresa) ISSN 1853-0400 (en línea) El mundo de las plantas en los últimos 130 millones de años: el Museo y sus investigadores como propulsores del conocimiento Abstract: The world of plants in the last 130 million years: The Museum and its researchers as propellants of knowledge. the magnificence and diversity of the extant flora, with plants adapted to almost all environments and latitudes throughout the world have originated, and originate, innumerable questions to all who study its fossil record. this Museum and its researchers have played a leading role in answering many of these questions almost from the very beginning. In early stages of the Museum the fossil plant record was highlighted by Hermann Burmeister and Florentino Ameghino, among others. After 1951, with the formation of the Paleobotany division, the discipline began to have a significant rise in the Museum with growing and progressive incorporation of researchers, increase of scientific collections and the transfer of knowledge through scientific meetings and publications in renowned national and international journals. In this context, it is worth noting the task conducted by dr. Alberto castellanos and the first Heads of the Paleobotany division: drs. carlos Menéndez (1951), Wolfgang Volkheimer (1975 and Sergio Archangelsky (1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) who laid the foundations that would position the Museum as one of the most important centers in Argentina on the study of Paleobotany.

The extant regional vegetation of Panotla, Tlaxcala, Mexico, is the result of its geography, mainly due to the buildup of the Mexican Trans-volcanic Belt. Before this volcanic belt originated, palaeobotanical evidence suggests that topographic, palaeoclimatic and ecological conditions were different, allowing the establish- ment of an evergreen tropical forest represented by plants similar to Terminalia, Cedrela and cf. Hypodaphnys, which together suggest the presence of a warm–humid (tropical) climate in a region not higher than 900 masl. In contrast, today Panotla is located at an altitude that varies from 2100 to 2300 masl, has a temperate sub-humid climate, with annual precipitation of 1650 mm, maximum annual temperature of 24.3 °C, and its vegetation is composed of a white pine (Pinus pseudostrobus Lindol.), oak (Quercus spp.) and white cedar (Cupressus benthamii Endl.). Geological and palaeobiological evidence suggests an active volcanic and tectonic scenario that influenced plant evolution by shifting climatic conditions from high temperature- humid to high temperature-dry, selecting the plant communities in the region through time, supporting the change from a tropical rain forest to a xeric vegetation.

Gynoecial morphology of Magnolia grandiflora is revised, with ‘follicles’ reinterpreted as condensed branching
systems forming a flower-like syncupulate infructescence (‘secondary flower). Flowers appear on the main axis in the axils or on basal ramifications of gynoecial paracladia, those developing into fruits being incased by glandular calyptras, commonly perceived as seeds. Fruit wall is formed of zygomorphic corolla tube with persistent calyx and petaloid tepals, containing a solitary inverted seed in the fertile locule, with analogies in diverse ‘eudicots’. These findings imply a reconsideration of ‘basal angiosperms’.

area. The phases of maximum fragmentation, which appear to have been connected with only the coldest periodsin the last instance during the second part of isotopic stages 6 (from c. 160 to 130000 years) and 2 (from c. 24 to 12 O00 years BP)relate to less than 10% of the last 800 O00 years, and the phases of maximum forest extension would likewise appear to be less than 10% of the period. The remaining 80-90% of the time relates to 'intermediate situations' which varied from period to period, and these intermediate extension situations seem to have been the norm over the larger part of the Quaternary, rather than the present situation which is closer to a situation of maximum extension. Fonds Documentaire ORSTOM Cote :

Polyploid genomes evolve and follow a series of dynamic transfigurations along with adaptation and speciation. The initial formation of a new polyploid individual within a diploid population usually involves a triploid bridge, a two-step mechanism of cell fusions between ubiquitous (reduced) and rare (unreduced) gametes. The primary fusion event creates an intermediate triploid individual with unbalanced genome sets, a situation of genomic-shock characterized by gene expression dysregulation, high dosage sensitivity, disturbed cell divisions, and physiological and reproductive attributes drastically altered. This near-sterile neotriploid must produce (even) eupolyploids through secondary fusion events to restore genome steadiness, meiotic balance, and fertility required for the demographic establishment of a nascent lineage. Natural conditions locate several difficulties to polyploid establishment, including the production of highly unbalanced and rarely unreduced (euploid) gametes, frequency-dependent disadvantages (minority cytotype exclusion), severe fitness loss, and ecological competition with diploid parents. Persistence and adaptation of neopolyploids depend upon genetic and phenotypic novelty coupled to joint selective forces that preserve shock-induced genomic changes (subgenome homeolog partitioning) and drive meiotic (reproductive) stabilization and ecological diversification. Thus, polyploid establishment through the triploid bridge is a feasible but not ubiquitous process that requires a number of low-probability events and singular circumstances. Yet, frequencies of polyploids suggest that polyploid establishment is a pervasive process. To explain this disparity, and supported in experimental evidence, I propose that situations like hybridization and ploidy-state transitions associated to genomic shock and substantial developmental alterations can transiently activate apomixis as a mechanism to halt genomic instability and cancel factors restraining neopolyploid's sexual fertility, particularly in triploids. Apomixis –as a temporal alternative to sex– skip meiosis and syngamy, and thus can freeze genomic attributes, avoid unbalanced chromosomal segregation and increase the formation of unreduced euploid gametes, elude frequency-dependent reproductive disadvantages by parthenogenetic development of the embryo and permissive development of endosperm during seed formation, and increase the effective population size of the neopolyploid lineage favoring the formation rate of eupolyploids compared to aneuploids. The subsequent action of genome resilience mechanisms that alleviate transcriptomic shock and selection upon gene interactions might restore a stable
meiosis and sexual fertility within few generations, as observed in synthetic polyploids. Alternatively, provided that resilience mechanisms fail, the neopolyploid might retain apomixis and hold genomically and transcriptionally altered states for many generations.

Throughout the history of the classification of extant ferns (monilophytes) and lycophytes, familial and generic concepts have been in great flux. For the organisation of lycophytes and ferns in herbaria, books, checklists, indices and spore banks and on the internet, this poses a problem, and a standardized linear sequence of these plants is therefore in great need. We provide here a linear classification to the extant lycophytes and ferns based on current phylogenetic knowledge; this provides a standardized guide for organisation of fern collections into a more natural sequence. Two new families, Diplaziopsidaceae and Rhachidosoraceae, are here introduced.

Here, the coevolution of mycorrhizal fungi and roots is assessed in the light of evidence now available, from palaeobotanical and morphological studies and the analysis of DNA-based phylogenies. The first bryophyte-like land plants, in the early Devonian (400 million years ago), had endophytic associations resembling vesiculararbuscular mycorrhizas (VAM) even before roots evolved. Mycorrhizal evolution would have progressed from endophytic hyphae towards balanced associations where partners were interdependent due to the exchange of limiting energy and nutrient resources. Most mycorrhizas are mutualistic, but in some cases the trend for increasing plant control of fungi culminates in the exploitative mycorrhizas of achlorophyllous, mycoheterotrophic plants. Ectomycorrhizal, ericoid and orchid mycorrhizas, as well as nonmycorrhizal roots, evolved during the period of rapid angiosperm radiation in the Cretaceous. It is hypothesised that roots gradually evolved from rhizomes to provide more suitable habitats for mycorrhizal fungi and provide plants with complex branching and leaves with water and nutrients. Selection pressures have caused the morphological divergence of roots with different types of mycorrizas. Root cortex thickness and exodermis suberization are greatest in obligately mycorrhizal plants, while nonmycorrhizal plants tend to have fine roots, with more roots hairs and relatively advanced chemical defences. Major coevolutionary trends and the relative success of plants with different root types are discussed.

To gain insights into the nature of the mitochondrial genome in the common ancestor of all green plants, we have completely sequenced the mitochondrial DNA (mtDNA) of Mesostigma viride. This green alga belongs to a morphologically heterogeneous class (Prasinophyceae) that includes descendants of the earliest diverging green plants. Recent phylogenetic analyses of ribosomal RNAs (rRNAs) and concatenated proteins encoded by the chloroplast genome identified Mesostigma as a basal branch relative to the Streptophyta and the Chlorophyta, the two phyla that were previously thought to contain all extant green plants. The circular mitochondrial genome of Mesostigma resembles the mtDNAs of green algae occupying a basal position within the Chlorophyta in displaying a small size (42,424 bp) and a high gene density (86.6% coding sequences). It contains 65 genes that are conserved in other mtDNAs. Although none of these genes represents a novel coding sequence among green plant mtDNAs, four of t...

• Premise of the Study: Secondary xylem (wood) produced by a vascular cambium supports increased plant size and underpins
the most successful model of arborescence among tracheophytes. Woody plants established the extensive forest ecosystems that dramatically changed the Earth’s biosphere. Secondary growth evolved in several lineages in the Devonian, but only two occurrences have been reported previously from the Early Devonian. The evolutionary history and phylogeny of wood production are poorly understood, and Early Devonian plants are key to illuminating them.
• Methods: A fossil plant preserved anatomically by cellular permineralization in the Lower Devonian (Emsian, ca. 400–395
million years old) Battery Point Formation of Gaspé Bay (Quebec, Canada) is described using the cellulose acetate peel
technique.
• Key Results: The plant, Franhueberia gerriennei Hoffman et Tomescu gen. et sp. nov., is a basal euphyllophyte with a centrarch protostele and metaxylem tracheids with circular and oval to scalariform bordered multiaperturate pits (P-type tracheids). The outer layers of xylem, consisting of larger-diameter P-type tracheids, exhibit the features diagnostic of secondary xylem: radial fi les of tracheids, multiplicative divisions, and a combination of axial and radial components.
• Conclusions: Franhueberia is one of the three oldest euphyllophytes exhibiting secondary growth documented in the Early Devonian. Within the euphyllophyte clade, these plants represent basal lineages that predate the evolution of stem-leaf-root organography and indicate that underlying mechanisms for secondary growth became part of the euphyllophyte developmental toolkit very early in the clade’s evolution.

Recent advances in molecular phylogenetics and a series of important palaeobotanical discoveries have revolutionized our understanding of angiosperm diversification. Yet, the origin and early evolution of their most characteristic feature, the flower, remains poorly understood. In particular, the structure of the ancestral flower of all living angiosperms is still uncertain. Here we report model-based reconstructions for ancestral flowers at the deepest nodes in the phylogeny of angiosperms, using the largest data set of floral traits ever assembled. We reconstruct the ancestral angiosperm flower as bisexual and radially symmetric , with more than two whorls of three separate perianth organs each (undifferentiated tepals), more than two whorls of three separate stamens each, and more than five spirally arranged separate carpels. Although uncertainty remains for some of the characters, our reconstruction allows us to propose a new plausible scenario for the early diversification of flowers, leading to new testable hypotheses for future research on angiosperms.

Most evolutionary studies of oceanic islands have focused on the Pacific Ocean. There are very few examples from the Atlantic archipelagos, especially Macaronesia, despite their unusual combination of features, including a close proximity to the continent, a broad range of geological ages, and a biota linked to a source area that existed in the Mediterranean basin before the late Tertiary. A chloroplast DNA (cpDNA) restriction site analysis of Argyranthemum (Asteraceae: Anthemideae), the largest endemic genus of plants of any volcanic archipelago in the Atlantic Ocean, was performed to examine patterns of plant evolution in Macaronesia. cpDNA data indicated that Argyranthemum is a monophyletic group that has speciated recently. The cpDNA tree showed a weak correlation with the current sectional

Leaf and cupule/nut remains belonging to Fagus (beech) have previously been reported from three plant-bearing formations on Iceland, the 15 Ma Selárdalur-Botn Formation, the 13.5 Ma Dufansdalur-Ketilseyri Formation, and the ca. 9-8 Ma SkarWstrfnd-Mó kollsdalur Formation, and have traditionally been assigned to various species. In this paper, we study Fagus leaves and cupules from the Miocene of Iceland based on unpublished and newly collected material and assess their taxonomic position. Leaves from Selárdalur (15 Ma) and Tafla (13.5 Ma) are described as a new species, Fagus friedrichii, on grounds of unique combinations of morphological features such as the large elliptical leaves with densely spaced secondary veins, the attenuate leaf apex, and the consistently craspedodromous venation.

Shaping Plant Evolution Amborella trichopoda is understood to be the most basal extant flowering plant and its genome is anticipated to provide insights into the evolution of plant life on Earth (see the Perspective by Adams ). To validate and assemble the sequence, Chamala et al. (p. 1516 ) combined fluorescent in situ hybridization (FISH), genomic mapping, and next-generation sequencing. The Amborella Genome Project (p. 10.1126/science.1241089 ) was able to infer that a whole-genome duplication event preceded the evolution of this ancestral angiosperm, and Rice et al. (p. 1468 ) found that numerous genes in the mitochondrion were acquired by horizontal gene transfer from other plants, including almost four entire mitochondrial genomes from mosses and algae.

The colonization of the epiphytic niche of Neotropical forest canopies played an important role in orchid's extraordinary diversification, with rare reversions to the terrestrial habit. To understand the evolutionary context of those reversals, we investigated the diversification of Galeandra, a Neotropical orchid genus which includes epiphytic and terrestrial species. We hypothesized that reversion to the terrestrial habit accompanied the expansion of savannas. To test this hypothesis we generated a comprehensive time-calibrated phylogeny and employed comparative methods. We found that Galeandra originated towards the end of the Miocene in Amazonia. The terrestrial clade originated synchronously with the rise of dry vegetation biomes in the last 5 million years, suggesting that aridification dramatically impacted plant diversification and habits in the Neotropics. Shifts in habit impacted floral spur lengths and geographic range size, but not climatic niche. The longer spurs and narrower ranges characterize epiphytic species, which probably adapted to specialized long-tongued Euglossini bee pollinators inhabiting forested habits. The terrestrial species present variable floral spurs and wider distribution ranges, with evidence of self-pollination, suggesting the loss of specialized pollination system and concomitant range expansion. Our study highlights how climate change impacted habit evolution and associated traits such as mutualistic interactions with pollinators.

Los aguacates son un fruto de importancia comercial en el mundo y fuente de miles de empleos a nivel global. Sin embargo, este fruto es un anacronismo, un fantasma evolutivo de una era en la que megabestias se alimentaban del fruto y lo dispersaban. Al extinguirse los gigantescos animales, los aguacates debieron seguirles el paso hacia la tumba, pero un mamífero recién llegado del viejo mundo los salvó de su extinción. Descubre el resto en este artículo sobre fantasmas evolutivos.

Polyploidization is a basic feature of plant evolution. Nearly all of the main food, cotton and oil crops are polyploid. When ploidy levels increase, yields double; this phenomenon suggested a new strategy of rice breeding that utilizes wide crosses and polyploidization dual advantages to breed super rice. Because low seed set rates in polyploid rice usually makes it difficult to breed, the selection of Ph-liked gene lines was emphasized. After progenies of indica-japonica were identified and selected, two polyploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The procedure included seven steps: selecting parents, crossing or multiple crossing, back-crossing, doubling chromosomes, identifying the polyploid, and choosing plants with high seed set rates that can breed themselves into stable lines. The characteristics of PMeS were determined by observing meiotic behaviors and by cross-identification of seed sets. PMeS-1 and PMeS-2, (japonica rice), have several characteristics different from other polyploid rice lines, including a higher rate of seed set (more than 65%, increasing to more than 70% in their F1 offspring); and stable meiotic behaviors (pairing with bivalents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromosomes in metaphase and without micronuclei in anaphase and telophase). The latter was obviously different from control polyploid line Dure-4X, which displayed abnormal meiotic behaviors including a higher rate of multivalents, univalents and trivalents in prophase, lagging chromosomes in metaphase and micronuclei in anaphase and telophase. There were also three differences of the breeding method between PMeS lines and normal diploid lines: chromosomes doubling, polyploidism identifying and higher seed set testing. The selection of PMeS lines is the first step in polyploid rice breeding; their use will advance the progress of polyploid rice breeding, which will in turn offer a new way to breed super rice.

This paper describes a system for simulating the evolution of artificial 2D plant morphologies. Virtual plant genotypes are inspired by the mathematical formalism known as Lindenmayer systems (L-systems). The phenotypes are the branching structures resulting from the derivation and graphic interpretation of the genotypes. Evolution is simulated using a genetic algorithm with a fitness function inspired by current evolutionary hypotheses concerning the factors that have had the greatest effect on plant evolution. The system also provides interactive selection, allowing the user to direct simulated evolution towards preferred phenotypes. Simulation results demonstrate many interesting structures, suggesting that artificial evolution constitutes a powerful tool for (1) exploring the large, complex space of branching structures found in nature, and (2) generating novel ones. Finally, we emphasize that Lindenmayer systems constitute a highly suitable encoding for artificial evolution studies.

MIKC-type proteins represent a class of MADS-domain transcription factors and are defined by a unique domain structure: in addition to the highly conserved DNA-binding MADS-domain, they have three other domains (dIT, dKT and dCT), with the keratin-like K-domain being the most highly conserved and characteristic one. The number and functional diversity of MIKC-type proteins increased considerably during land plant evolution, culminating in higher flowering plants, where they dominate the control of reproductive development from early to late stages. We wonder how one special class of proteins became important in the control of essentially all stages of a morphogenetic process. All MADS-domain proteins appear to bind to DNA as homo-or heterodimers and may function as part of ternary transcription factor complexes involving non-MADS-domain proteins. Only MIKC-type proteins, however, generate complex intrafamily interaction networks. These are based on the special potential of MIKC-type proteins to form complexes involving more than two homologous proteins constituting transcriptional regulators. We speculate that the potential to form heteromultimers of homologous proteins was achieved by the acquisition of the K-domain during evolution. There is emerging evidence that organismal complexity arises from progressively more elaborate regulation of gene expression. We hypothesize that combinatorial multimer formation of MIKC-type MADS-domain proteins facilitated an unusually efficient and rapid functional diversification based on gene duplication, sequence divergence and fixation. This dnetworkingT may have enabled a more sophisticated transcriptional control of target genes which was recruited for controlling increasingly complex and diverse developmental pathways during the rapid origin and diversification of plant reproductive structures. Therefore, MIKC-type proteins may owe their evolutionary dsuccessT and present-day developmental importance in part to their modular domain structure. Investigating the evolution of MIKC-type genes may thus help to better understand origin and diversification of gene regulatory networks. D

During the past decade, enormous progress has been made in understanding the molecular regulation of flower development. In particular, homeotic genes that determine the identity of the floral organs have been characterised from different flowering plants, revealing considerable conservation among angiosperm species. On the other hand, evolutionary diversification has led to enormous variation in flower morphology. Increasing numbers of reports have described differences in the regulation, redundancy and function of homeotic genes from various species. These fundamentals of floral organ specification are therefore an ideal subject for comparative analyses of flower development, which will lead to a better understanding of plant evolution, plant development and the complexity of molecular mechanisms that control flower development and morphology.

New morphometric data gathered from cross-sections of two Lower Devonian land plants (Rhynia gwynne-vaughanii and Asteroxylon mackiei) are interpreted in terms of the evolution of the function of vascular bundles in early land plants. The following conclusions can be drawn from these new data: (1) The ratio of the cross-sectional area of the xylem (representing the conducting volume supplying the axis with water) to the xylem perimeter (representing the ''contact area'' between xylem and parenchyma through which water leaves the xylem and enters the parenchyma) is not constant for Rhynia axes, almost constant for Asteroxylon axes, and different between Rhynia and Asteroxylon. Thus, Bowers hypothesis that the ratio of cross-sectional area of the xylem to xylem perimeter is constant during ontogenetic development is true for Asteroxylon. That this ratio is constant during phylogeny, however, is not supported by our data. (2) The ratio between cross-sectional area of xylem to parenchyma is higher in Asteroxylon than in Rhynia. (3) As predicted by previous computer simulations, the ratio of the xylem perimeter to the axis perimeter plays a major role in determining water transport performance of the transpiring axis. This ratio is constant within ontogeny but is different in Asteroxylon and Rhynia. In Asteroxylon axes, this ratio is about twice as large as in Rhynia axes. (4) Contrary to the expectations, the distance between the outermost layer of the xylem and the transpiring surface, which represents the low-conductivity pathway through the parenchyma, appears not to be a limiting factor for the water transport in axes of Rhynia and Asteroxylon. (5) From the analysis of the geometric parameters, it is evident that Rhynia and Asteroxylon with their distinct stelar geometries represent two different constructional types for which no transitional stages are known.

F-box proteins are substrate-recognition components of the Skp1-Rbx1-Cul1-F-box protein (SCF) ubiquitin ligases. In plants, F-box genes form one of the largest multigene superfamilies and control many important biological functions. However, it is unclear how and why plants have acquired a large number of F-box genes. Here we identified 692, 337, and 779 F-box genes in Arabidopsis, poplar and rice, respectively, and studied their phylogenetic relationships and evolutionary patterns. We found that the plant F-box superfamily can be divided into 42 families, each of which has a distinct domain organization. We also estimated the number of ancestral genes for each family and identified highly conservative versus divergent families. In conservative families, there has been little or no change in the number of genes since the divergence between eudicots and monocots Ϸ145 million years ago. In divergent families, however, the numbers have increased dramatically during the same period. In two cases, the numbers of genes in extant species are >100 times greater than that in the most recent common ancestor (MRCA) of the three species. Proteins encoded by highly conservative genes always have the same domain organization, suggesting that they interact with the same or similar substrates. In contrast, proteins of rapidly duplicating genes sometimes have quite different domain structures, mainly caused by unusually frequent shifts of exon-intron boundaries and/or frameshift mutations. Our results indicate that different F-box families, or different clusters of the same family, have experienced dramatically different modes of sequence divergence, apparently having resulted in adaptive changes in function.