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    The Angiosperm Terrestrial Revolution and the origins of modern biodiversity

    Biodiversity today has the unusual property that 85% of plant and animal species live on land rather than in the sea, and half of these live in tropical rainforests. An explosive boost to terrestrial...

    New PhytologistVolume 233, Issue 5 p. 2017-2035

    Tansley review Open Access

    The Angiosperm Terrestrial Revolution and the origins of modern biodiversity

    Michael J. Benton , Peter Wilf , Hervé Sauquet

    First published: 26 October 2021

    https://doi.org/10.1111/nph.17822

    Citations: 8

    Summary

    Biodiversity today has the unusual property that 85% of plant and animal species live on land rather than in the sea, and half of these live in tropical rainforests. An explosive boost to terrestrial diversity occurred from . 100–50 million years ago, the Late Cretaceous and early Palaeogene. During this interval, the Earth-life system on land was reset, and the biosphere expanded to a new level of productivity, enhancing the capacity and species diversity of terrestrial environments. This boost in terrestrial biodiversity coincided with innovations in flowering plant biology and evolutionary ecology, including their flowers and efficiencies in reproduction; coevolution with animals, especially pollinators and herbivores; photosynthetic capacities; adaptability; and ability to modify habitats. The rise of angiosperms triggered a macroecological revolution on land and drove modern biodiversity in a secular, prolonged shift to new, high levels, a series of processes we name here the Angiosperm Terrestrial Revolution.

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    The Angiosperm Terrestrial Revolution and the origins of modern biodiversity

    by Benton et al. Contents Summary 2017

    I. Introduction 2017

    II. Can the Angiosperm Terrestrial Revolution be quantified? 2018

    III. Evolutionary patterns among plants and fungi 2020

    IV. Evolutionary patterns among animals 2021

    V. Angiosperms are unique among land plants 2025

    VI. Impacts of angiosperms 2028

    VII. Physical drivers of the Angiosperm Terrestrial Revolution 2029

    VIII. Future directions 2030

    Acknowledgements 2031

    References 2031

    I. Introduction

    Most of life's diversity is on land. It is estimated that there are 10–15 million species of animals, plants, and fungi on Earth today (Costello ., 2012; Monastersky, 2014; Christenhusz & Byng, 2016; Stork, 2018), and some 85% of these live on land, even though the oceans cover 71% of the Earth's surface (Wiens, 2015). Macroscopic life today (i.e. excluding microbes) is dominated in numerical terms by species of insects, spiders and relatives, flowering plants and fungi, and vertebrates such as lizards, birds, and mammals. An intriguing observation (Vermeij & Grosberg, 2010) is that biodiversity on land may have exceeded marine biodiversity since 110 million years ago (Ma); why the switchover?

    Terrestrialization began by the Ordovician and Silurian, when plants and animals ventured onto land, and more complex ecosystems emerged in the Early Devonian. Although arborescence had already evolved in several lineages of vascular plants, the evolution of seeds in the Late Devonian enabled trees to colonize nearly all of Earth's surface, changing weathering and atmospheric cycles forever (Algeo & Scheckler, 1998; Morris ., 2018). The Carboniferous–Permian deglaciation and the 252 Ma end-Permian mass extinction each reset the nature of terrestrial ecosystems substantially, and many new groups of plants and animals originated or diversified in the ensuing Triassic, 252–201 Ma (Looy ., 2001; Montañez ., 2007; Benton, 2010, 2016). Further significant changes began in the Cretaceous, 145–66 Ma, which coincided with the rise of the angiosperms, the flowering plants (Crane ., 1995; Herendeen ., 2017; Magallón ., 2019). Events of this time have been called the Cretaceous Terrestrial Revolution (KTR; Lloyd ., 2008) because many of the most species-rich living clades of terrestrial plants and animals originated then, as shown by numerous fossils and molecular phylogenetic studies of vertebrates (Alfaro ., 2009; Meredith ., 2011), insects (Peters ., 2017; Espeland ., 2018; Kawahara ., 2019; McKenna ., 2019), and plants (Wing & Boucher, 1998; Herendeen ., 2017; Magallón ., 2019; Ramírez-Barahona ., 2020). However, it has become increasingly clear that some of the most significant events in the rise of angiosperms occurred during the early Paleogene, and it is time to revise the KTR concept.

    In our view, the KTR was part of a more protracted change in terrestrial ecosystems driven by angiosperms and lasting minimally from 100–50 Ma, through the Late Cretaceous and early Palaeogene (Fig. 1). This interval ranges from the appearance of highly diverse angiosperm leaf floras, when angiosperms first had more species than other plants (Crane ., 1995; Herendeen ., 2017), to the Early Eocene Climatic Optimum (EECO) when features of many modern ecosystems had emerged around the world, including angiosperm dominance, very high biodiversity, and the presence of numerous angiosperm crown lineages (Jaramillo ., 2010). This prolonged series of events can be missed because it is punctuated by the famous Cretaceous–Palaeogene mass extinction (KPME), 66 Ma, when dinosaurs and other land organisms died out along with . 70% of marine species, and so triggering the explosion of modern mammals, birds, and lizards (Slater, 2013; Field ., 2019). For land plants, the KPME had devastating effects, punctuating the diversification of the angiosperms and altering the trajectory of their evolution (Nichols & Johnson, 2008; Vajda & Bercovici, 2014). This is especially clear in the development of modern-style Neotropical rainforests. The KPME caused a 45% loss of plant diversity in Colombia, followed by 6 million years (Myr) of slow recovery and the appearance of several of today's characteristic, dominant Neotropical plant families (Carvalho ., 2021); later, rapid warming at the Palaeocene–Eocene Thermal Maximum (PETM) and sustained warmth during the EECO brought originations of many more significant tropical taxa and diversification (Jaramillo ., 2010). Other warming events during the rise of angiosperms, including two Ocean Anoxic Events (OAEs) in the Early and Late Cretaceous, had major impacts on life in the sea but perhaps had smaller impacts on terrestrial ecosystems or angiosperm evolution (Crane & Lidgard, 1989; Huber ., 2018; Magallón ., 2019). Thus, the definitive emergence of biodiverse, angiosperm-dominated forests and continuing restructuring of terrestrial ecosystems occurred in the Paleogene, and the whole long-recognized (Crane ., 1995; Wing & Boucher, 1998; Wing ., 2012; Herendeen ., 2017; Magallón ., 2019) but often overlooked process might be better termed the Angiosperm Terrestrial Revolution (ATR), spanning both the Late Cretaceous and the early Palaeogene. This proposed term is not intended to minimize the significance of preceding or subsequent events involving angiosperms but rather to highlight the long interval from the first appearance of high angiosperm diversity (. 100 Ma) to their overwhelming dominance in biodiverse terrestrial ecosystems (. 50 Ma).

    Source : nph.onlinelibrary.wiley.com

    Evolution of Seed Plants

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    Seed Plants

    Evolution of Seed Plants

    Evolution of Seed Plants The Evolution of Seed Plants and Adaptations for Land

    The evolution of seeds allowed plants to reproduce independently of water; pollen allows them to disperse their gametes great distances.

    LEARNING OBJECTIVES

    Recognize the significance of seed plant evolution

    KEY TAKEAWAYS

    Key Points

    Plants are used for food, textiles, medicines, building materials, and many other products that are important to humans.

    The evolution of seeds allowed plants to decrease their dependency upon water for reproduction.

    Seeds contain an embryo that can remain dormant until conditions are favorable when it grows into a diploid sporophyte.

    Seeds are transported by the wind, water, or by animals to encourage reproduction and reduce competition with the parent plant.

    Key Terms

    seed: a fertilized ovule, containing an embryonic plantsporophyte: a plant (or the diploid phase in its life cycle) that produces spores by meiosis in order to produce gametophytespollen: microspores produced in the anthers of flowering plants

    Evolution of Seed Plants

    The lush palms on tropical shorelines do not depend upon water for the dispersal of their pollen, fertilization, or the survival of the zygote, unlike mosses, liverworts, and ferns of the terrain. Seed plants, such as palms, have broken free from the need to rely on water for their reproductive needs. They play an integral role in all aspects of life on the planet, shaping the physical terrain, influencing the climate, and maintaining life as we know it. For millennia, human societies have depended upon seed plants for nutrition and medicinal compounds; and more recently, for industrial by-products, such as timber and paper, dyes, and textiles. Palms provide materials including rattans, oils, and dates. Wheat is grown to feed both human and animal populations. The fruit of the cotton boll flower is harvested as a boll, with its fibers transformed into clothing or pulp for paper. The showy opium poppy is valued both as an ornamental flower and as a source of potent opiate compounds.

    Seed plants dominate the landscape: Seed plants dominate the landscape and play an integral role in human societies. (a) Palm trees grow along the shoreline; (b) wheat is a crop grown in most of the world; (c) the flower of the cotton plant produces fibers that are woven into fabric; (d) the potent alkaloids of the beautiful opium poppy have influenced human life both as a medicinal remedy and as a dangerously-addictive drug.

    Seeds and Pollen as an Evolutionary Adaptation to Dry Land

    Unlike bryophyte and fern spores (which are haploid cells dependent on moisture for rapid development of gametophytes ), seeds contain a diploid embryo that will germinate into a sporophyte. Storage tissue to sustain growth and a protective coat give seeds their superior evolutionary advantage. Several layers of hardened tissue prevent desiccation, freeing reproduction from the need for a constant supply of water. Furthermore, seeds remain in a state of dormancy induced by desiccation and the hormone abscisic acid until conditions for growth become favorable. Whether blown by the wind, floating on water, or carried away by animals, seeds are scattered in an expanding geographic range, thus avoiding competition with the parent plant.

    Pollen grains are male gametophytes carried by wind, water, or a pollinator. The whole structure is protected from desiccation and can reach the female organs without dependence on water. Male gametes reach female gametophyte and the egg cell gamete though a pollen tube: an extension of a cell within the pollen grain. The sperm of modern gymnosperms lack flagella, but in cycads and the Gingko, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.

    Fossilized pollen grains: This fossilized pollen is from a Buckbean fen core found in Yellowstone National Park, Wyoming. The pollen is magnified 1,054 times.

    Evolution of Gymnosperms

    Seed ferns gave rise to the gymnosperms during the Devonian Period, allowing them to adapt to dry conditions.

    LEARNING OBJECTIVES

    Explain how and why gymnosperms became the dominant plant group during the Permian period

    KEY TAKEAWAYS

    Key Points

    Seed ferns were the first seed plants, protecting their reproductive parts in structures called cupules.

    Seed ferns gave rise to the gymnosperms during the Paleozoic Era, about 390 million years ago.

    Gymnosperms include the gingkoes and conifers and inhabit many ecosystems, such as the taiga and the alpine forests, because they are well adapted for cold weather.

    Source : courses.lumenlearning.com

    Angiosperms – Biology 2e

    134 ANGIOSPERMS

    Learning Objectives

    By the end of this section, you will be able to do the following:

    Explain why angiosperms are the dominant form of plant life in most terrestrial ecosystems

    Describe the main parts of a flower and their functions

    Detail the life cycle of a typical gymnosperm and angiosperm

    Discuss the similarities and differences between the two main groups of flowering plants

    From their humble and still obscure beginning during the early Jurassic period, the angiosperms—or flowering plants—have evolved to dominate most terrestrial ecosystems ((Figure)). With more than 300,000 species, the angiosperm phylum (Anthophyta) is second only to insects in terms of diversification.

    Flowers. These flowers grow in a botanical garden border in Bellevue, WA. Flowering plants dominate terrestrial landscapes. The vivid colors of flowers and enticing fragrance of flowers are adaptations to pollination by animals like insects, birds, and bats. (credit: Myriam Feldman)

    The success of angiosperms is due to two novel reproductive structures: flowers and fruits. The function of the flower is to ensure pollination, often by arthropods, as well as to protect a developing embryo. The colors and patterns on flowers offer specific signals to many pollinating insects or birds and bats that have coevolved with them. For example, some patterns are visible only in the ultraviolet range of light, which can be seen by arthropod pollinators. For some pollinators, flowers advertise themselves as a reliable source of nectar. Flower scent also helps to select its pollinators. Sweet scents tend to attract bees and butterflies and moths, but some flies and beetles might prefer scents that signal fermentation or putrefaction. Flowers also provide protection for the ovule and developing embryo inside a receptacle. The function of the fruit is seed protection and dispersal. Different fruit structures or tissues on fruit—such as sweet flesh, wings, parachutes, or spines that grab—reflect the dispersal strategies that help spread seeds.

    Flowers

    Flowers are modified leaves, or sporophylls, organized around a central receptacle. Although they vary greatly in appearance, virtually all flowers contain the same structures: sepals, petals, carpels, and stamens. The peduncle typically attaches the flower to the plant proper. A whorl of sepals (collectively called the calyx) is located at the base of the peduncle and encloses the unopened floral bud. Sepals are usually photosynthetic organs, although there are some exceptions. For example, the corolla in lilies and tulips consists of three sepals and three petals that look virtually identical. Petals, collectively the corolla, are located inside the whorl of sepals and may display vivid colors to attract pollinators. Sepals and petals together form the perianth. The sexual organs, the female gynoecium and male androecium are located at the center of the flower. Typically, the sepals, petals, and stamens are attached to the receptacle at the base of the gynoecium, but the gynoecium may also be located deeper in the receptacle, with the other floral structures attached above it.

    As illustrated in (Figure), the innermost part of a perfect flower is the gynoecium, the location in the flower where the eggs will form. The female reproductive unit consists of one or more carpels, each of which has a stigma, style, and ovary. The stigma is the location where the pollen is deposited either by wind or a pollinating arthropod. The sticky surface of the stigma traps pollen grains, and the style is a connecting structure through which the pollen tube will grow to reach the ovary. The ovary houses one or more ovules, each of which will ultimately develop into a seed. Flower structure is very diverse, and carpels may be singular, multiple, or fused. (Multiple fused carpels comprise a pistil.) The androecium, or male reproductive region is composed of multiple stamens surrounding the central carpel. Stamens are composed of a thin stalk called a filament and a sac-like structure called the anther. The filament supports the anther, where the microspores are produced by meiosis and develop into haploid pollen grains, or male gametophytes.

    Flower structure. This image depicts the structure of a perfect flower. Perfect flowers produce both male and female floral organs. The flower shown has only one carpel, but some flowers have a cluster of carpels. Together, all the carpels make up the gynoecium. (credit: modification of work by Mariana Ruiz Villareal)

    The Life Cycle of an Angiosperm

    The adult or sporophyte phase is the main phase of an angiosperm’s life cycle ((Figure)). Like gymnosperms, angiosperms are heterosporous. Therefore, they produce microspores, which will generate pollen grains as the male gametophytes, and megaspores, which will form an ovule that contains female gametophytes. Inside the anther’s microsporangia, male sporocytes divide by meiosis to generate haploid microspores, which, in turn, undergo mitosis and give rise to pollen grains. Each pollen grain contains two cells: one generative cell that will divide into two sperm and a second cell that will become the pollen tube cell.

    Source : opentextbc.ca

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