Plant Diversity I: How Plants Colonized Land

Plant Diversity I: How Plants Colonized Land
Chapter 29 Plant Diversity I: How Plants Colonized Land

Fig. 29-1 Figure 29.1 How did plants change the world? For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless

Concept 29.1: Land plants evolved from green algae
Green algae called charophytes are the closest relatives of land plants

Morphological and Molecular Evidence
Many characteristics of land plants also appear in a variety of algal clades, mainly algae However, land plants share four key traits only with charophytes: Rose-shaped complexes for cellulose synthesis Peroxisome enzymes Structure of flagellated sperm Formation of a phragmoplast

Comparisons of both nuclear and chloroplast genes point to charophytes as the closest living relatives of land plants Note that land plants are not descended from modern charophytes, but share a common ancestor with modern charophytes

5 mm 40 µm Chara species, a pond organism Coleochaete orbicularis, a
Fig. 29-3 Chara species, a pond organism 5 mm Coleochaete orbicularis, a disk-shaped charophyte that also lives in ponds (LM) Figure 29.3 Examples of charophytes, the closest algal relatives of land plants 40 µm

Adaptations Enabling the Move to Land
In charophytes a layer of a durable polymer called sporopollenin prevents exposed zygotes from drying out The movement onto land by charophyte ancestors provided unfiltered sun, more plentiful CO2, nutrient-rich soil, and few herbivores or pathogens Land presented challenges: a scarcity of water and lack of structural support

The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants Systematists are currently debating the boundaries of the plant kingdom Some biologists think the plant kingdom should be expanded to include some or all green algae Until this debate is resolved, we will retain the embryophyte definition of kingdom Plantae

Red algae ANCESTRAL ALGA Chlorophytes Viridiplantae Charophytes
Fig. 29-4 Red algae ANCESTRAL ALGA Chlorophytes Viridiplantae Charophytes Figure 29.4 Three possible “plant” kingdoms Streptophyta Embryophytes Plantae

Derived Traits of Plants
Four key traits appear in nearly all land plants but are absent in the charophytes: Alternation of generations (with multicellular, dependent embryos) Walled spores produced in sporangia Multicellular gametangia Apical meristems

Additional derived traits such as a cuticle and secondary compounds evolved in many plant species
Symbiotic associations between fungi and the first land plants may have helped plants without true roots to obtain nutrients

Alternation of generations
Fig. 29-5a Gamete from another plant Gametophyte (n) Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION Zygote 2n Figure 29.5 Derived traits of land plants Mitosis Sporophyte (2n) Alternation of generations

Placental transfer cell (outlined in blue)
Fig. 29-5b Embryo 2 µm Maternal tissue Figure 29.5 Derived traits of land plants Wall ingrowths 10 µm Placental transfer cell (outlined in blue) Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort)

Longitudinal section of Sphagnum sporangium (LM)
Fig. 29-5c Spores Sporangium Longitudinal section of Sphagnum sporangium (LM) Figure 29.5 Derived traits of land plants Sporophyte Gametophyte Sporophytes and sporangia of Sphagnum (a moss)

Archegonia and antheridia of Marchantia (a liverwort)
Fig. 29-5d Archegonium with egg Female gametophyte Antheridium with sperm Figure 29.5 Derived traits of land plants Male gametophyte Archegonia and antheridia of Marchantia (a liverwort)

Apical meristem of shoot Developing leaves Apical meristems
Fig. 29-5e Apical meristem of shoot Developing leaves Apical meristems Figure 29.5 Derived traits of land plants Apical meristem of root Shoot Root 100 µm 100 µm

Fig. 29-6 (a) Fossilized spores Fossil evidence indicates that plants were on land at least 475 million years ago Figure 29.6 Ancient plant spores and tissue (colorized SEMs) (b) Fossilized sporophyte tissue

Table 29-1 Club mosses ferns Table 29.1

Figure 29.7 Highlights of plant evolution
1 Origin of land plants (about 475 mya) 2 Origin of vascular plants (about 420 mya) 3 Origin of extant seed plants (about 305 mya) Liverworts Nonvascular plants (bryophytes) Land plants ANCES- TRAL GREEN ALGA 1 Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Seedless vascular plants 2 Vascular plants Pterophytes (ferns, horsetails, whisk ferns) Figure 29.7 Highlights of plant evolution Gymnosperms 3 Seed plants Angiosperms 500 450 400 350 300 50 Millions of years ago (mya)

Bryophyte Gametophytes
In all three bryophyte phyla, gametophytes are larger and longer-living than sporophytes Sporophytes are typically present only part of the time

Figure 29.8 The life cycle of a moss
Raindrop Sperm “Bud” Antheridia Male gametophyte (n) Key Haploid (n) Protonemata (n) Diploid (2n) “Bud” Egg Spores Gametophore Archegonia Spore dispersal Female gametophyte (n) Rhizoid Peristome Sporangium FERTILIZATION Figure 29.8 The life cycle of a moss MEIOSIS (within archegonium) Seta Zygote (2n) Capsule (sporangium) Mature sporophytes Foot Embryo Archegonium Young sporophyte (2n) 2 mm Capsule with peristome (SEM) Female gametophytes

Polytrichum commune, hairy-cap moss Sporophyte (a sturdy Capsule
Fig. 29-9d Polytrichum commune, hairy-cap moss Sporophyte (a sturdy plant that takes months to grow) Capsule Seta Figure 29.9 Bryophyte diversity Gametophyte

(a) Peat being harvested
Fig (a) Peat being harvested Figure Sphagnum, or peat moss: a bryophyte with economic, ecological, and archaeological significance (b) “Tollund Man,” a bog mummy

Concept 29.3: Ferns and other seedless vascular plants were the first plants to grow tall
Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution Vascular plants began to diversify during the Devonian and Carboniferous periods Vascular tissue allowed these plants to grow tall Seedless vascular plants have flagellated sperm and are usually restricted to moist environments

Origins and Traits of Vascular Plants
Fossils of the forerunners of vascular plants date back about 420 million years These early tiny plants had independent, branching sporophytes Living vascular plants are characterized by: Life cycles with dominant sporophytes Vascular tissues called xylem and phloem Well-developed roots and leaves

Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte
Fig Key Haploid (n) Diploid (2n) Spore (n) Antheridium Young gametophyte Spore dispersal MEIOSIS Sporangium Mature gametophyte (n) Sperm Archegonium Egg Mature sporophyte (2n) Sporangium New sporophyte Zygote (2n) FERTILIZATION Sorus Figure The life cycle of a fern Gametophyte Fiddlehead

Transport in Xylem and Phloem
Vascular plants have two types of vascular tissue: xylem and phloem Xylem conducts most of the water and minerals and includes dead cells called tracheids Phloem consists of living cells and distributes sugars, amino acids, and other organic products Water-conducting cells are strengthened by lignin and provide structural support Increased height was an evolutionary advantage

Evolution of Roots Roots are organs that anchor vascular plants They enable vascular plants to absorb water and nutrients from the soil Roots may have evolved from subterranean stems

Evolution of Leaves Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy that is used for photosynthesis

Fig Figure Artist’s conception of a Carboniferous forest based on fossil evidence

Alternation of generations Apical meristems
Fig. 29-UN4 Apical meristem of shoot Developing leaves Gametophyte Mitosis Mitosis n n n n Spore Gamete MEIOSIS FERTILIZATION 2n Zygote Mitosis Haploid Sporophyte Diploid 1 Alternation of generations 2 Apical meristems Archegonium with egg Antheridium with sperm Sporangium Spores 3 Multicellular gametangia 4 Walled spores in sporangia

Plant Diversity II: The Evolution of Seed Plants
Chapter 30 Plant Diversity II: The Evolution of Seed Plants

Fig. 30-1 A seed consists of an embryo and nutrients surrounded by a protective coat Figure 30.1 What human reproductive organ is functionally similar to this seed?

In addition to seeds, the following are common to all seed plants
Concept 30.1: Seeds and pollen grains are key adaptations for life on land In addition to seeds, the following are common to all seed plants Reduced gametophytes Heterospory Ovules Pollen

Fig. 30-2 PLANT GROUP Mosses and other nonvascular plants Ferns and other seedless vascular plants Seed plants (gymnosperms and angiosperms) Reduced, independent (photosynthetic and free-living) Reduced (usually microscopic), dependent on surrounding sporophyte tissue for nutrition Gametophyte Dominant Reduced, dependent on gametophyte for nutrition Sporophyte Dominant Dominant Gymnosperm Angiosperm Sporophyte (2n) Microscopic female gametophytes (n) inside ovulate cone Microscopic female gametophytes (n) inside these parts of flowers Sporophyte (2n) Gametophyte (n) Example Figure 30.2 Gametophyte/sporophyte relationships in different plant groups Microscopic male gametophytes (n) inside these parts of flowers Microscopic male gametophytes (n) inside pollen cone Sporophyte (2n) Sporophyte (2n) Gametophyte (n)

Figure 30.3 From ovule to seed in a gymnosperm
Seed coat (derived from integument) Integument Female gametophyte (n) Spore wall Egg nucleus (n) Immature female cone Food supply (female gametophyte tissue) (n) Male gametophyte (within a germinated pollen grain) (n) Megasporangium (2n) Discharged sperm nucleus (n) Embryo (2n) (new sporophyte) Megaspore (n) Micropyle Pollen grain (n) Figure 30.3 From ovule to seed in a gymnosperm (a) Unfertilized ovule (b) Fertilized ovule (c) Gymnosperm seed

Concept 30.2: Gymnosperms bear “naked” seeds, typically on cones
The gymnosperms have “naked” seeds not enclosed by ovaries and consist of four phyla: Cycadophyta (cycads) Gingkophyta (one living species: Ginkgo biloba) Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia) Coniferophyta (conifers, such as pine, fir, and redwood)

Living seed plants can be divided into two clades: gymnosperms and angiosperms
Gymnosperms appear early in the fossil record and dominated the Mesozoic terrestrial ecosystems Gymnosperms were better suited than nonvascular plants to drier conditions Today, cone-bearing gymnosperms called conifers dominate in the northern latitudes

Phylum Cycadophyta Individuals have large cones and palmlike leaves These thrived during the Mesozoic, but relatively few species exist today

Fig. 30-5a Figure 30.5 Gymnosperm diversity Cycas revoluta

Phylum Ginkgophyta This phylum consists of a single living species, Ginkgo biloba It has a high tolerance to air pollution and is a popular ornamental tree

Ginkgo biloba pollen-producing tree
Fig. 30-5b Figure 30.5 Gymnosperm diversity Ginkgo biloba pollen-producing tree

Ginkgo biloba leaves and fleshy seeds
Fig. 30-5c Figure 30.5 Gymnosperm diversity Ginkgo biloba leaves and fleshy seeds

Phylum Gnetophyta This phylum comprises three genera Species vary in appearance, and some are tropical whereas others live in deserts

Fig. 30-5d Figure 30.5 Gymnosperm diversity Gnetum

Fig. 30-5e Figure 30.5 Gymnosperm diversity Ephedra

Fig. 30-5f Figure 30.5 Gymnosperm diversity Welwitschia

Fig. 30-5g Ovulate cones Figure 30.5 Gymnosperm diversity Welwitschia

Phylum Coniferophyta This phylum is by far the largest of the gymnosperm phyla Most conifers are evergreens and can carry out photosynthesis year round

Fig. 30-5h Figure 30.5 Gymnosperm diversity Douglas fir

Fig. 30-5i Figure 30.5 Gymnosperm diversity European larch

Fig. 30-5j Figure 30.5 Gymnosperm diversity Bristlecone pine

Fig. 30-5k Figure 30.5 Gymnosperm diversity Sequoia

Fig. 30-5l Figure 30.5 Gymnosperm diversity Wollemi pine

Fig. 30-5m Figure 30.5 Gymnosperm diversity Common juniper

Surviving megaspore (n) Seedling
Fig Key Haploid (n) Ovule Diploid (2n) Ovulate cone Megasporocyte (2n) Integument Pollen cone Microsporocytes (2n) Mature sporophyte (2n) Megasporangium (2n) Pollen grain Pollen grains (n) MEIOSIS MEIOSIS Microsporangia Microsporangium (2n) Surviving megaspore (n) Seedling Archegonium Figure 30.6 The life cycle of a pine Seeds Female gametophyte Food reserves (n) Sperm nucleus (n) Seed coat (2n) Pollen tube Embryo (2n) FERTILIZATION Egg nucleus (n)

Concept 30.3: The reproductive adaptations of angiosperms include flowers and fruits
Angiosperms are seed plants with reproductive structures called flowers and fruits They are the most widespread and diverse of all plants All angiosperms are classified in a single phylum, Anthophyta The name comes from the Greek anthos, flower

Stigma Carpel Stamen Anther Style Filament Ovary Petal Sepal Ovule
Fig. 30-7 Stigma Carpel Stamen Anther Style Filament Ovary Figure 30.7 The structure of an idealized flower Petal Sepal Ovule

Modes of seed dispersal?
Fig. 30-8 Tomato Ruby grapefruit Modes of seed dispersal? Nectarine A fruit typically consists of a mature ovary but can also include other flower parts Figure 30.8 Some variations in fruit structure Hazelnut Milkweed

Wings Seeds within berries Barbs Fig. 30-9
Figure 30.9 Fruit adaptations that enhance seed dispersal Barbs

Mature flower on sporophyte plant (2n) Microsporocytes (2n)
Fig Key Haploid (n) Diploid (2n) Microsporangium Anther Mature flower on sporophyte plant (2n) Microsporocytes (2n) MEIOSIS Generative cell Microspore (n) Ovule (2n) Tube cell Male gametophyte (in pollen grain) (n) Ovary Pollen grains MEIOSIS Germinating seed Stigma Megasporangium (2n) Pollen tube Embryo (2n) Endosperm (3n) Seed coat (2n) Sperm Seed Megaspore (n) Style Antipodal cells Central cell Synergids Egg (n) Figure The life cycle of an angiosperm Female gametophyte (embryo sac) Pollen tube Sperm (n) Nucleus of developing endosperm (3n) FERTILIZATION Zygote (2n) Egg nucleus (n) Discharged sperm nuclei (n)

Angiosperms originated at least 140 million years ago
Fig Carpel Stamen 5 cm (a) Archaefructus sinensis, a 125-million-year-old fossil Figure A primitive flowering plant? (b) Artist’s reconstruction of Archaefructus sinensis Angiosperms originated at least 140 million years ago

Angiosperm Diversity The two main groups of angiosperms are monocots (one cotyledon) and eudicots (“true” dicots) The clade eudicot includes some groups formerly assigned to the paraphyletic dicot (two cotyledons) group

Basal angiosperms are less derived and include the flowering plants belonging to the oldest lineages
Magnoliids share some traits with basal angiosperms but are more closely related to monocots and eudicots

Basal Angiosperms Three small lineages constitute the basal angiosperms These include Amborella trichopoda, water lilies, and star anise

Fig a Figure Angiosperm diversity Amborella trichopoda

Fig b Figure Angiosperm diversity Water lily

Fig c Figure Angiosperm diversity Star anise

Magnoliids Magnoliids include magnolias, laurels, and black pepper plants Magnoliids are more closely related to monocots and eudicots than basal angiosperms

Fig d Figure Angiosperm diversity Southern magnolia

Monocots More than one-quarter of angiosperm species are monocots

Fig e Figure Angiosperm diversity Orchid

Pygmy date palm (Phoenix roebelenii)
Fig e1 Figure Angiosperm diversity Pygmy date palm (Phoenix roebelenii)

Fig f Figure Angiosperm diversity

Barley Anther Stigma Ovary Filament Fig. 30-13g
Figure Angiosperm diversity Anther Stigma Ovary Filament

Eudicots More than two-thirds of angiosperm species are eudicots

Fig h Figure Angiosperm diversity California poppy

Fig i Figure Angiosperm diversity Pyrenean oak

Fig j Figure Angiosperm diversity Dog rose

Fig k Figure Angiosperm diversity Snow pea

Fig l Figure Angiosperm diversity Zucchini flowers

Figure 30.13 Angiosperm diversity
Fig m Monocot Characteristics Eudicot Characteristics Embryos One cotyledon Two cotyledons Leaf venation Veins usually parallel Veins usually netlike Stems Vascular tissue usually arranged in ring Vascular tissue scattered Roots Root system usually fibrous (no main root) Taproot (main root) usually present Figure Angiosperm diversity Pollen Pollen grain with one opening Pollen grain with three openings Flowers Floral organs usually in multiples of three Floral organs usually in multiples of four or five

Chapter 31 Fungi

Fig. 31-1 Figure 31.1 Can you spot the largest organism in this forest?

Concept 31.1: Fungi are heterotrophs that feed by absorption
Fungi are heterotrophs and absorb nutrients from outside of their body Fungi use enzymes to break down a large variety of complex molecules into smaller organic compounds The versatility of these enzymes contributes to fungi’s ecological success

Reproductive structure
Fig. 31-2 Reproductive structure Hyphae Spore-producing structures Figure 31.2 Structure of a multicellular fungus 20 µm Mycelium

Specialized Hyphae in Mycorrhizal Fungi
Some unique fungi have specialized hyphae called haustoria that allow them to penetrate the tissues of their host

(a) Hyphae adapted for trapping and killing prey
Fig. 31-4 Hyphae Nematode 25 µm (a) Hyphae adapted for trapping and killing prey Plant cell wall Fungal hypha Figure 31.4 Specialized hyphae Plant cell Plant cell plasma membrane Haustorium (b) Haustoria

Concept 31.2: Fungi produce spores through sexual or asexual life cycles
Fungi propagate themselves by producing vast numbers of spores, either sexually or asexually Fungi can produce spores from different types of life cycles

Haploid (n) Heterokaryotic stage Heterokaryotic (unfused nuclei from
Fig Key Haploid (n) Heterokaryotic stage Heterokaryotic (unfused nuclei from different parents) PLASMOGAMY (fusion of cytoplasm) Diploid (2n) KARYOGAMY (fusion of nuclei) Spore-producing structures Zygote SEXUAL REPRODUCTION Spores ASEXUAL REPRODUCTION Mycelium Figure 31.5 Generalized life cycle of fungi MEIOSIS GERMINATION GERMINATION Spores

Fig. 31-6 2.5 µm Figure 31.6 Penicillium, a mold commonly encountered as a decomposer of food

Fig. 31-7 10 µm Parent cell Figure 31.7 The yeast Saccharomyces cerevisiae in several stages of budding (SEM) Bud

Concept 31.3: The ancestor of fungi was an aquatic, single-celled, flagellated protist
DNA evidence suggests that fungi are most closely related to unicellular nucleariids while animals are most closely related to unicellular choanoflagellates This suggests that fungi and animals evolved from a common flagellated unicellular ancestor and multicellularity arose separately in the two groups The oldest undisputed fossils of fungi are only about 460 million years old

Fig. 31-9 Figure 31.9 Fossil fungal hyphae and spores from the Ordovician period (about 460 million years ago) (LM) 50 µm

Figure 31.11 Fungal diversity
Hyphae 25 µm Chytrids (1,000 species) Zygomycetes (1,000 species) Fungal hypha Glomeromycetes (160 species) Ascomycetes (65,000 species) Figure Fungal diversity Basidiomycetes (30,000 species)

They can be decomposers, parasites, or mutualists
Chytrids Chytrids (phylum Chytridiomycota) are found in freshwater and terrestrial habitats They can be decomposers, parasites, or mutualists Molecular evidence supports the hypothesis that chytrids diverged early in fungal evolution Chytrids are unique among fungi in having flagellated spores, called zoospores Video: Allomyces Zoospore Release Video: Phlyctochytrium Zoospore Release

Fig Figure Flagellated chytrid zoospore (TEM) Flagellum 4 µm

Zygomycetes The zygomycetes (phylum Zygomycota) exhibit great diversity of life histories They include fast-growing molds, parasites, and commensal symbionts The zygomycetes are named for their sexually produced zygosporangia Zygosporangia, which are resistant to freezing and drying, can survive unfavorable conditions

Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) Mating
Fig Key Haploid (n) Heterokaryotic (n + n) Diploid (2n) PLASMOGAMY Mating type (+) Gametangia with haploid nuclei Mating type (–) 100 µm Young zygosporangium (heterokaryotic) Rhizopus growing on bread SEXUAL REPRODUCTION Dispersal and germination Zygosporangium Sporangia KARYOGAMY Figure The life cycle of the zygomycete Rhizopus stolonifer (black bread mold) Spores Diploid nuclei Sporangium ASEXUAL REPRODUCTION MEIOSIS Dispersal and germination 50 µm Mycelium

Some zygomycetes, such as Pilobolus, can actually “aim” their sporangia toward conditions associated with good food sources

Fig Figure Pilobolus aiming its sporangia 0.5 mm

Ascomycetes Ascomycetes (phylum Ascomycota) live in marine, freshwater, and terrestrial habitats The phylum is defined by production of sexual spores in saclike asci, usually contained in fruiting bodies called ascocarps Ascomycetes are commonly called sac fungi Ascomycetes vary in size and complexity from unicellular yeasts to elaborate cup fungi and morels

Tuber melanosporum, a truffle
Fig Morchella esculenta, the tasty morel Tuber melanosporum, a truffle Figure Ascomycetes (sac fungi)

Basidiomycetes Basidomycetes (phylum Basidiomycota) include mushrooms, puffballs, and shelf fungi, mutualists, and plant parasites The phylum is defined by a clublike structure called a basidium, a transient diploid stage in the life cycle The basidiomycetes are also called club fungi

Fig Maiden veil fungus (Dictyphora), a fungus with an odor like rotting meat Puffballs emitting spores Shelf fungi, important decomposers of wood Figure Basidiomycetes (club fungi)

Dikaryotic mycelium Haploid mycelia Mating type (–) Mating type (+)
Fig Dikaryotic mycelium Haploid mycelia PLASMOGAMY Mating type (–) Mating type (+) Gills lined with basidia Haploid mycelia SEXUAL REPRODUCTION Basidiocarp (n+n) Dispersal and germination Basidiospores (n) Basidium with four basidiospores Basidia (n+n) Basidium Figure The life cycle of a mushroom-forming basidiomycete Basidium containing four haploid nuclei KARYOGAMY MEIOSIS Key Haploid (n) Dikaryotic (n +n) Diploid nuclei 1 µm Basidiospore Diploid (2n)

Lichens A lichen is a symbiotic association between a photosynthetic microorganism and a fungus in which millions of photosynthetic cells are held in a mass of fungal hyphae

Crustose (encrusting) lichens A foliose (leaflike) lichen
Fig Crustose (encrusting) lichens A fruticose (shrublike) lichen A foliose (leaflike) lichen Figure Variation in lichen growth forms

Staphylococcus Penicillium Zone of inhibited growth Fig. 31-26
Figure Fungal production of an antibiotic

Plant Diversity I: How Plants Colonized Land

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