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Ch 17/31 The Origin and Diversification of Plants
Fossil evidence indicates that plants were on land at least 475 million years ago Fossilized spores and tissues have been extracted from 475-million-year-old rocks
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(a) Fossilized spores (b) Fossilized sporophyte tissue Fig. 29-6
Figure 29.6 Ancient plant spores and tissue (colorized SEMs) (b) Fossilized sporophyte tissue
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Overview: The Greening of Earth
Looking at a lush landscape, it is difficult to imagine the land without any plants or other organisms For more than the first 3 billion years of Earth’s history, the terrestrial surface was lifeless Since colonizing land, plants have diversified into roughly 290,000 living species Plants supply oxygen and are the ultimate source of most food eaten by land animals
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Fig. 29-1 Figure 29.1 How did plants change the world?
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Concept 29.1: Land plants evolved from green algae
Green algae called charophytes are the closest relatives of land plants
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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
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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
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The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants Scientist 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
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Plant charcteristics Biologist classify plants into divisions
A Biologist that studies plants is a Botanist Plants are organized into tissue/organs Plants are eukaryotic with a cell wall of cellulose Plants are considered autotrophs They use the process of photosynthesis in which light is captured by the pigment chlorophyll
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Plants are divided into divisions based on vascular tissue.
Having vascular tissue determines how water is moved through a plants
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Alternation of Generations and Multicellular, Dependent Embryos
Plants alternate between two multicellular stages, a reproductive cycle called alternation of generations The gametophyte is haploid and produces haploid gametes by mitosis = sexual stage Fusion of the gametes gives rise to the diploid sporophyte, which produces haploid spores by meiosis = asexual stage
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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)
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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
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The accumulation of traits that facilitated survival on land may have opened the way to its colonization by plants
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Adaptations needed for plants to survive
need a constant supply of water need sunlight for photosynthesis need to transport water and nutrients against gravity need to be able to reproduce with/without water How do plants solve this problem ?
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live in swamps and marshes grow tall with roots, stems and leaves that hold up the plant to the sun and transport water and nutrients use vascular tissue in side the stem to move water against gravity waxy outer cuticle to protect leaves from the sun use pollen - pollination by insects, no need for movement of gametes by water
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Those ancestral species gave rise to a vast diversity of modern plants
Land plants can be informally grouped based on the presence or absence of vascular tissue Nonvascular plants are commonly called bryophytes Bryophytes the simplest plants, no true roots stems or leaves, cells on the leaf are one cell thick
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Nonvascular plants (bryophytes)
Fig. 29-UN1 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms
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Mosses are most closely related to vascular plants
Concept 29.2: Mosses and other nonvascular plants have life cycles dominated by gametophytes Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants: Liverworts Hornworts Mosses Mosses are most closely related to vascular plants
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Marchantia polymorpha, a “thalloid” liverwort
Fig. 29-9a Gametophore of female gametophyte Thallus Sporophyte Foot Seta Figure 29.9 Bryophyte diversity Capsule (sporangium) Marchantia polymorpha, a “thalloid” liverwort 500 µm Marchantia sporophyte (LM)
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An Anthoceros hornwort species Sporophyte Gametophyte Fig. 29-9c
Figure 29.9 Bryophyte diversity Gametophyte
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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
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The Ecological and Economic Importance of Mosses
Moses are capable of inhabiting diverse and sometimes extreme environments, but are especially common in moist forests and wetlands Some mosses might help retain nitrogen in the soil Bryophytes and bryophyte-like plants were the prevalent vegetation during the first 100 million years of plant evolution
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Sphagnum, or “peat moss,” forms extensive deposits of partially decayed organic material known as peat Sphagnum is an important global reservoir of organic carbon
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(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
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Multicellular Gametangia
Gametes (sperm and egg) are produced within organs called gametangia Male gametangia, called antheridia, are the site of sperm production and release Female gametangia, called archegonia, produce eggs and are the site of fertilization Sporophyte produces spores, formed by the gametes
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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)
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Animation: Moss Life Cycle
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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
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Ferns and other seedless vascular plants were the first plants to grow tall
Most plants have vascular tissue; these are called Tracheophytes Vascular tissue allowed these plants to grow tall The sun drives evaporation which moves water through the plant , and adhesion and cohesion Sugar moves by pressure, root pressure allows for a little movement
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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 Phloem consists of living cells and distributes sugars, amino acids, and other organic products All plants that have vascular tissue are Tracheophytes (which have 9 divisions)
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Nonvascular plants (bryophytes)
Fig. 29-UN2 Nonvascular plants (bryophytes) Seedless vascular plants Gymnosperms Angiosperms
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spore plants are Seedless vascular plants which can be divided into
Lycophytes club mosses and their relatives Pterophytes ferns and their relatives
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Diphasiastrum tristachyum, a club moss
Fig d 2.5 cm Strobili (clusters of sporophylls) Figure Seedless vascular plant diversity Diphasiastrum tristachyum, a club moss
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Equisetum arvense, field horsetail Vegetative stem Strobilus on
Fig g Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem Figure Seedless vascular plant diversity 1.5 cm
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The Significance of Seedless Vascular Plants
The ancestors of modern lycophytes, horsetails, and ferns grew to great heights during the Devonian and Carboniferous, forming the first forests Increased photosynthesis may have helped produce the global cooling at the end of the Carboniferous period The decaying plants of these Carboniferous forests eventually became coal
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Fig Figure Artist’s conception of a Carboniferous forest based on fossil evidence
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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
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TRACHEOPHYTES Any plant with a seed Gymnosperms and Angiosperms
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A seed is protective by an outer covering called a seed coat
Which protects the embryo Seed plants can be divided into further groups: Gymnosperms, the “naked seed” plants, with a woody stem including the conifers, ginkgo, cycads, ivy, holly, rhododendron and mt. laurel Angiosperms, the flowering plants, broad leaves, herbaceous stem (green) include petunias, dandelions, lily, grass, corn
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Gymnosperms
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Angiosperms
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Angiosperms have two groups based on an embryonic leaf called a cotyledon
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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
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Monocots vs Dicots
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Table 29-1 Table 29.1
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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)
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